Join for FREE
It only takes a minute!

Welcome to BirdForum.
BirdForum is the net's largest birding community, dedicated to wild birds and birding, and is absolutely FREE! You are most welcome to register for an account, which allows you to take part in lively discussions in the forum, post your pictures in the gallery and more.

Reply
 
Thread Tools Rate Thread
Old Wednesday 4th August 2010, 21:26   #1
looksharp65
Registered User
 
looksharp65's Avatar

 
Join Date: Feb 2010
Location: Varberg, Sweden
Posts: 1,603
AFOV, focus speed and common beliefs

Sorry about the title. After 15 minutes of thinking, I could not come up with anything better.

So guys (Henry, Kevin, Frank, Steve et al), I would like to ask you a couple of things that are a bit puzzling to me.

Let's begin with apparent field of view. We all know how to compute it roughly by multiplicating the magnification with the true field of view. And I am a big AFOV fan. A big AFOV provides a "Wow!" experience and simplifies the targeting.
I can't really see the need for pinsharp edges if the downside is a narrow TFOV/AFOV.

Anyway, it is not a secret that a couple of my bins have an AFOV of about 56 degrees. I would have wanted more but I can handle it.

The thing is, I use eyeglasses most of the time, and occasionally contacts.
When using glasses, and the eyecups are down, I have a feeling that the AFOV is greater. Of course it is not, but the "Wow!" comes when using glasses. When eyecups are extracted, and that wide black rim surrounds the image, I somehow get a feeling of tunnel vision. And reversely, when the eyecups are retracted so the rim appears thinner, the field seems to widen.

This leads me to thinking, if the ocular ends of the binocular's barrels are as thin as possible, and the exit pupil as large as possible, and the eye-relief generous, the "Wow!" experience would be granted. The "real AFOV" is easy to compute, but does it necessarily express what the perceived vision through a given binocular is like?

-----------------------------

The other thing I would like to make a comment upon is about the speed of the focusing knob. Here and elsewhere, it is defined in terms of "one and a half rotation from closest focus to infinity".

The problem with this generalization is that binoculars have different closest focus. And the closer, the close end of the knob rotation needs increasingly more space.
My Minox is a fast-focuser with only one full rotation from close to infinity, but it takes a few "jumps" with the finger to reach infinity. (The depth-of-field is quite shallow in this model)

But my Vortex can focus a lot closer, and needs something like 1,25 rotations from closest to infinity. Its depth-of-field is tremendeous however, so in real use, I rarely move the knob more than about 50 degrees, which is easy to do without "jumping" with the index finger.

I believe that a more veracious description of focusing speed would be obtained if we settled for a close focus of 3 m/10 ft, and then how many degrees of turning it takes to get the first sharp focus on infinity. That is, for binoculars with deep depth-of-field, when focused to the hyperfocal distance.
For binoculars with shallow DOF, it will take more turns to reach infinity.

The eyesight, pupil size and age of the individual tester will probably make some difference here but I guess the results could be made quite reliable if there is a reference binocular involved in the game.

Waiting for your gathered wisdom to comment upon this.

Kind regards

/L


__________________
http://en.wikipedia.org/wiki/Visby_lenses - The Viking optics
http://www.youtube.com/watch?v=LuBYpRkbzrs - The Viking War Cry
looksharp65 is offline  
Reply With Quote
Old Thursday 5th August 2010, 01:41   #2
Steve C
Registered User

 
Join Date: Jun 2007
Location: Klamath Basin, Oregon
Posts: 2,639
I think the point is well taken. I really have no real idea of just how to address it. People are different from each other and prefer different things including binoculars. I do tend to think that people tend to obsess way too much about certain facets of "comparative binocular analysis". I tend to think that most people would be far better served to take a few binoculars from a list that you compile however you compile it. From reviews and comments here, from observations of friends binoculars, or observations from a store and if one suits you, the just get it and use it. The thing is that wondering if a brand x would be better than my brand y will usually just drive you nuts.

As far as focus speed goes, I have binoculars that go from a silky smooth fast one turn or even less to 2+ turns. Some go clockwise, some counterclockwise. I have no preference and could care less. Give me a few minutes and the thing is ingrained and I get along just fine. But users really like some certain point on the focus continuum. So yes you are probably right in that the focus should be defined in terms of particular distance parameters. Also close in birding with some butterflies thrown in for good measure is a different need set than waterfowl over some distances.

I really pay no particular attention to AFOV (just goes to show everybody is different), other than to pay some lip service to if it is wide angle or not. I can take 50* or so AFOV just fine, 60* is about right and much more than that seems superfluous to me. Get the field too wide and other things like pincushion, edge sharpness, and field curvature become more problematic. I also do not need glasses with binoculars despite having 62 year old eyes. I will use linear FOV more as a measure, but the thing is after a while you look through enough binoculars that you can get a pretty rapid "go or no go" determination, not necessarily a final performance grade, but is it good enough to warrant further inspection. It sometimes takes quite some time to sort out just what it was that caught your attention. Sometimes it is more obvious. AFOV in combination with some other aspects of the image presented may well be part of it. Sometimes other things beside AFOV will win the day, who knows. I have the idea youi never can tell just how one particular set of eyes will react to any particular binocular.

You will also never get a perfect binocular. They are kind of like your friends. They all have faults. So when you get a new binocular see if you can live successfuly with its strengths and forget about weaknesses, unless glaring. There is a process everybody goes through to get to the point where you feel somewhat comfortable with what you buy. I have a bunch of stuff for sale and am reducing my stable to maybe three or four. I still look at anything I have never seen before, but am far less inclined these days to make a deal on a new one. But I have no doubt something is out there that will reach out and grab my attention.
__________________
Steve

"Do what you can, where you are, with what you have" Teddy Roosevelt.
Steve C is offline  
Reply With Quote
BF Supporter 2009
Click here to Support BirdForum
Old Thursday 5th August 2010, 19:27   #3
FrankD
Registered User

 
Join Date: Feb 2005
Location: Eastern Pennsylvania
Posts: 7,120
Hey, I have been out of the loop for awhile so my own part of the "collective wisdom" won't amount to much. If this was a year ago I probably would have more to say.

For starters, yes, you can use the magnification times the degree field of view equation to get a rough estimate on the anguler field of view. If I remember correctly though, based on a conversation that Kevin and I had, the lower you go in the magnification range (7-8x) the less it is accurate. There is an equation to determine the true angular field of view. Kevin probably knows it.

As for a general comment on that issue, yes, I do prefer a wider angular field of view to a narrower one. I love the Nikon E II 8x30 and the Zeiss 7x42 FL because of this. Their true fields of view are huge for their respective powers. This coupled with the depth of field gives the user an extremely satisfying viewing experience.

To touch about what you were trying to relate about eye relief, eyecup/ocular edge diameter, etc... I think I know what you are referring to. I think of the Meopta Meostar with this one. The ocular lens is huge and the rim around it is fairly small in comparison. It has a nice walk-in view because of this and, with reference to the 8x42 specifically, the huge true and apparent field of view make the image addicting.

Eye relief has a lot to do with this. I received a similar impression with the original Nikon Venturer 8x42. It has a large ocular lens and fairly narrow rims on the eyecups plus it has very generous eye relief. Also worth noting is that both bins utilized field flatteners in the design which makes the edges nearly as sharp as the center. All of it contributes to the "experience".

As for focusing speed....I don't really have a preference. If pressed I would say I prefer at least one turn. Focusing tension is much more an issue with me. I prefer there to be enough resistance in correlation with the focusing speed....and it needs to be consistant in both directions.

Hope this helps some.

Last edited by FrankD : Thursday 5th August 2010 at 19:29.
FrankD is offline  
Reply With Quote
Old Thursday 5th August 2010, 23:06   #4
looksharp65
Registered User
 
looksharp65's Avatar

 
Join Date: Feb 2010
Location: Varberg, Sweden
Posts: 1,603
With this thread, I am trying to target two properties that have not been properly quantified, this far.
Steve, I partially agree with you in that binoculars should be tried before the buy. Maybe you are right about making so much noise about "comparative binocular analysis". But still, as we have entered this area, I feel it's right to explore it. Could there be ways to stretch the boundaries of how we describe binoculars technically, or should we just give up, letting it all be a matter of trial-and-error?

The focus speed thing is quite easy to address. I described my point of view in the original post.
The FOV/AFOV/walk-in subject (thanks, Frank!) takes a lot more effort to handle. Maybe I am obsessed by this particular property of a set of binoculars. When using them I tend to center the bird in the absolute center of the field, so absolute edge sharpness is not necessary for me. But a decent TFOV and consequently AFOV simplifies the targetting, and is one of the more important parts of the "Wow!" experience.
__________________
http://en.wikipedia.org/wiki/Visby_lenses - The Viking optics
http://www.youtube.com/watch?v=LuBYpRkbzrs - The Viking War Cry

Last edited by looksharp65 : Thursday 5th August 2010 at 23:23.
looksharp65 is offline  
Reply With Quote
Old Thursday 5th August 2010, 23:20   #5
looksharp65
Registered User
 
looksharp65's Avatar

 
Join Date: Feb 2010
Location: Varberg, Sweden
Posts: 1,603
Image #1 and #2 share the same TFOV, but #2 has more magnification, hence the AFOV of #2 is greater.

Image #1 and #3 roughly share the same AFOV, but #3 has more magnification, hence the TFOV is lesser in #3

Image #2 and #4 are identical, but the extended eyecups of #4 makes it look more like a tunnel.

I clearly prefer #1 and #2 before the two other images.
Attached Thumbnails
Click image for larger version

Name:	TFOVAFOV2.jpg
Views:	203
Size:	184.2 KB
ID:	276338  
__________________
http://en.wikipedia.org/wiki/Visby_lenses - The Viking optics
http://www.youtube.com/watch?v=LuBYpRkbzrs - The Viking War Cry
looksharp65 is offline  
Reply With Quote
Old Friday 6th August 2010, 00:43   #6
NDhunter
Registered User

 
Join Date: Mar 2009
Location: ND
Posts: 2,113
Quote:
Originally Posted by Steve C View Post
I think the point is well taken. I really have no real idea of just how to address it. People are different from each other and prefer different things including binoculars. I do tend to think that people tend to obsess way too much about certain facets of "comparative binocular analysis". I tend to think that most people would be far better served to take a few binoculars from a list that you compile however you compile it. From reviews and comments here, from observations of friends binoculars, or observations from a store and if one suits you, the just get it and use it. The thing is that wondering if a brand x would be better than my brand y will usually just drive you nuts.

As far as focus speed goes, I have binoculars that go from a silky smooth fast one turn or even less to 2+ turns. Some go clockwise, some counterclockwise. I have no preference and could care less. Give me a few minutes and the thing is ingrained and I get along just fine. But users really like some certain point on the focus continuum. So yes you are probably right in that the focus should be defined in terms of particular distance parameters. Also close in birding with some butterflies thrown in for good measure is a different need set than waterfowl over some distances.

I really pay no particular attention to AFOV (just goes to show everybody is different), other than to pay some lip service to if it is wide angle or not. I can take 50* or so AFOV just fine, 60* is about right and much more than that seems superfluous to me. Get the field too wide and other things like pincushion, edge sharpness, and field curvature become more problematic. I also do not need glasses with binoculars despite having 62 year old eyes. I will use linear FOV more as a measure, but the thing is after a while you look through enough binoculars that you can get a pretty rapid "go or no go" determination, not necessarily a final performance grade, but is it good enough to warrant further inspection. It sometimes takes quite some time to sort out just what it was that caught your attention. Sometimes it is more obvious. AFOV in combination with some other aspects of the image presented may well be part of it. Sometimes other things beside AFOV will win the day, who knows. I have the idea youi never can tell just how one particular set of eyes will react to any particular binocular.

You will also never get a perfect binocular. They are kind of like your friends. They all have faults. So when you get a new binocular see if you can live successfuly with its strengths and forget about weaknesses, unless glaring. There is a process everybody goes through to get to the point where you feel somewhat comfortable with what you buy. I have a bunch of stuff for sale and am reducing my stable to maybe three or four. I still look at anything I have never seen before, but am far less inclined these days to make a deal on a new one. But I have no doubt something is out there that will reach out and grab my attention.
Steve:

I agree with you all the way here, it is nice of you to take the time and bring out
that for many here, you can do all the reading and learning that you can, but it
does come down to you and "your eyes only".

Jerry
NDhunter is offline  
Reply With Quote
Old Friday 6th August 2010, 02:26   #7
FrankD
Registered User

 
Join Date: Feb 2005
Location: Eastern Pennsylvania
Posts: 7,120
looksharp,

What I took from your picture is basically a description of both a walk in view and what can be described as tunnel vision. Your description with the eyecups fully extended refers to this to an extent. The difference though is that, with the eyecups extended, eye relief is typically shortened and subsequently your field of view narrows because you are farther away from optimal eye relief. I ran into this problem with the Nikon EII 8x30 to an extent. With the eyecups rolled down (older style rubber in this case) I couldn't get the images to overlap because the IPD wouldn't go down low enough over the bridge of my nose. With the eyecups extended the eye relief was too short and I was left with a bit of tunnel vision (picture 3 or 4 take your pick). When I removed the eyecups completely I received the full field of view and correct eye relief thus giving that "walk-in" view.
FrankD is offline  
Reply With Quote
Old Friday 6th August 2010, 03:09   #8
Kevin Purcell
Registered User
 
Kevin Purcell's Avatar

 
Join Date: Jul 2008
Location: Seattle, WA
Posts: 3,778
Quote:
The thing is, I use eyeglasses most of the time, and occasionally contacts.
When using glasses, and the eyecups are down, I have a feeling that the AFOV is greater. Of course it is not, but the "Wow!" comes when using glasses. When eyecups are extracted, and that wide black rim surrounds the image, I somehow get a feeling of tunnel vision. And reversely, when the eyecups are retracted so the rim appears thinner, the field seems to widen.
This is an interesting optical illusion that I've seen a few times. It's very vivid.

I think the issue here is where the final aperature that just matches the vignetting aperture.

I've even seen this effect on "narrow" field bin with pop up eyecups. If you set the eyecups just right (just about vignetting the FOV) it appeared a lot bigger.

This points to the perceived AFOV being a perceptual issue which rather puts it beyond objective measure. A bit like the "roof magnification illusion" where the magnification of bins appears to change depending on objective lens separation.

Quote:
The problem with this generalization is that binoculars have different closest focus. And the closer, the close end of the knob rotation needs increasingly more space.
That's why it's better to use my (birding) standard of 3m/10feet to infinity. Pretty much all bins can do that so you get the same measure for all bins.

There is a thread with such measurement I've made in it ... you could add to it.

If you search here you can also find the thread on why depth of field is only dependent on magnification. Some believe it and some don't.

The confounding issue is focus rate and focus speed (something we've talked about before too). A high rate and fast focus bin will appear to have a narrow depth of field because you are liable to overshoot. In reality it has the same DOF as any other bin of the same magnification.

Again this is confounding perception of ergonomics with a measurable number (or two numbers in this case, perhaps three: rate, force and rate of change of force). Curiously, I have bins one of which goes from a 0.5 turn (for 3m to infinity) with "nice smooth speed" (EDG 8x32) to a u Elite 10x with 1.3 turns to infinity (also with a nice smooth but different speed) and both feel just right to me. See I'm not consistent so how anyone can expect to measure this is a problem beyond me.

Experience and serious handwaving is what you are left with for reviews. And it's about the best we have. Saying bin X is like bin Y but also a bit like bin Z is helpful if you've used bin Y and bin Z.

That and trusting or understanding the reviewer. If I know Henry's, or Frank's or Steve's or Sancho's (or even Dennis') reviewing quirks then I know how to recalibrate their review as it might relate to me.

In fact my recent experience with the EDG has lead me to understand NDHunter and Fireform a bit better than I did.

In the end binoculars are coupled to these odd things called humans. They're part of the system and you can't really avoid their quirks.
Kevin Purcell is offline  
Reply With Quote
Old Friday 6th August 2010, 06:35   #9
looksharp65
Registered User
 
looksharp65's Avatar

 
Join Date: Feb 2010
Location: Varberg, Sweden
Posts: 1,603
Quote:
Originally Posted by FrankD View Post
looksharp,

What I took from your picture is basically a description of both a walk in view and what can be described as tunnel vision. Your description with the eyecups fully extended refers to this to an extent. The difference though is that, with the eyecups extended, eye relief is typically shortened and subsequently your field of view narrows because you are farther away from optimal eye relief. I ran into this problem with the Nikon EII 8x30 to an extent. With the eyecups rolled down (older style rubber in this case) I couldn't get the images to overlap because the IPD wouldn't go down low enough over the bridge of my nose. With the eyecups extended the eye relief was too short and I was left with a bit of tunnel vision (picture 3 or 4 take your pick). When I removed the eyecups completely I received the full field of view and correct eye relief thus giving that "walk-in" view.
Apparently, your problem with the EII comes from both the optical and the physical construction of the binoculars. If your IPD is small, the folded rubber eyecups hit your nose so you can't get close enough to the eyepieces. And with the eyecups extracted, the eye-relief is too short.

I remember when Nikon announced their 35 mm F3 HP, that was aiming on bespectacled professional photographers.
Maybe "eye relief" should be renamed as "high eyepoint". The "high eyepoint" then would refer to the maximum eye-relief with the binoculars.
Because "eye-relief" basically stands for the actual distance between the cornea and the outer eyepiece lens, and it may vary within a range. Coming too close to the eyepiece, blackout will occur.
__________________
http://en.wikipedia.org/wiki/Visby_lenses - The Viking optics
http://www.youtube.com/watch?v=LuBYpRkbzrs - The Viking War Cry

Last edited by looksharp65 : Friday 6th August 2010 at 17:24.
looksharp65 is offline  
Reply With Quote
Old Friday 6th August 2010, 06:44   #10
looksharp65
Registered User
 
looksharp65's Avatar

 
Join Date: Feb 2010
Location: Varberg, Sweden
Posts: 1,603
Quote:
Originally Posted by Kevin Purcell View Post
This is an interesting optical illusion that I've seen a few times. It's very vivid.

I think the issue here is where the final aperature that just matches the vignetting aperture.

I've even seen this effect on "narrow" field bin with pop up eyecups. If you set the eyecups just right (just about vignetting the FOV) it appeared a lot bigger.

This points to the perceived AFOV being a perceptual issue which rather puts it beyond objective measure. A bit like the "roof magnification illusion" where the magnification of bins appears to change depending on objective lens separation.



That's why it's better to use my (birding) standard of 3m/10feet to infinity. Pretty much all bins can do that so you get the same measure for all bins.

There is a thread with such measurement I've made in it ... you could add to it.

If you search here you can also find the thread on why depth of field is only dependent on magnification. Some believe it and some don't.

I didn't know that you already had this idea of standard focus speed measurement! Now we're two!

I guess the construction of the optical system will have some impact on the DOF. The magnification has the most effect, though. A lesser magnification will also not magnify the blurred parts of the image, and this is why they appear sharper.
Probably the size of the exit pupil matters too, and possibly the range of usable eye-relief.

"The roof magnification illusion" partially comes from the offset of the bin's barrels (each tube will expand the lateral field of view as compared to a roof prism bin) , but also from the fact that a eyeball convergence is needed when you look at medium or close distance through a porro bin.
__________________
http://en.wikipedia.org/wiki/Visby_lenses - The Viking optics
http://www.youtube.com/watch?v=LuBYpRkbzrs - The Viking War Cry
looksharp65 is offline  
Reply With Quote
Old Friday 6th August 2010, 15:57   #11
Steve C
Registered User

 
Join Date: Jun 2007
Location: Klamath Basin, Oregon
Posts: 2,639
Quote:
Originally Posted by looksharp65 View Post
I didn't know that you already had this idea of standard focus speed measurement! Now we're two!
Seems like we got into this topic some months back. IIRC Kimmo Absetz (sorry in advance Kimmo if I got the last name wrong) started a post about fov measurements and I THINK that that post got eventually pretty well into the focus like you mention. Anyway, standardizing the focus distance as you and Kevin is a good idea.

Maybe it was not that thread from Kimmo, but there was quite a bit of discussion on the topic.
__________________
Steve

"Do what you can, where you are, with what you have" Teddy Roosevelt.
Steve C is offline  
Reply With Quote
BF Supporter 2009
Click here to Support BirdForum
Old Friday 6th August 2010, 20:26   #12
elkcub
Registered User
 
elkcub's Avatar

 
Join Date: Sep 2004
Location: Northern California
Posts: 2,947
Quote:
Originally Posted by looksharp65 View Post
Image #1 and #2 share the same TFOV, but #2 has more magnification, hence the AFOV of #2 is greater.

Image #1 and #3 roughly share the same AFOV, but #3 has more magnification, hence the TFOV is lesser in #3

Image #2 and #4 are identical, but the extended eyecups of #4 makes it look more like a tunnel.

I clearly prefer #1 and #2 before the two other images.
Looksharp,

I must commend you for introducing the very important topic of perceived FOV, as well as a stunning graphic demonstration (attached below).
Quote:
When using glasses, and the eyecups are down, I have a feeling that the AFOV is greater.

I've mentioned this effect on several occasions, but it was never discussed further. In fact, even in this thread the idea has almost slipped out of the conversation.

Anyway, I noticed the phenomenon a few years ago after acquiring my Zeiss 7x42 BGATP. With the eyecups fully extended the view seemed rather tunnel like, even though the true field is quite wide (450'). Using glasses with the eyecups rolled down, however, I perceived the view to be marvelously wide, and, I might add, perceptually larger. This is so dramatic for me that nowadays I only use the BGAT, and certain other binoculars, with glasses on.

What might account for this? Since with the BGAT I can see the circular field stop with or without glasses, effective eye relief does not appear to be involved. When looking though the fully extended eyecups, however, peripheral images are completely occluded (i.e., the unmagnified peripheral images). In fact, this is a real tunnel view, since the long eyecups provide a physical tunnel to look through. Using eyeglasses, however, the unmagnified peripheral images are included in the total view, and to some extent still function to provide useful visual information, e.g., object movements, visual horizon, etc. Moreover, normal visual field overlap is still present. The magnified view is essentially superimposed on the unmagnified binocular scene, which spans more than 180 deg for both eyes. A price that is paid for this is stray sidelight, which can compromise image contrast in some binoculars.

Just my thoughts on the subject, but, again, I find it surprising that this perceptual phenomenon hasn't been discussed at greater length. I would add that this beneficial property of eyeglasses also allows for the use of sunglasses, with or without a prescription. For some reason, this is another topic that is rarely discussed. If strong sunlight can hurt your eyes, it can also hurt your eyes using a binocular.

Ed

Note: In the above I distinguish between the apparent FOV vs its perception, which I refer to as the perceived FOV or PFOV. Within this framework, the AFOV physically corresponds with the image projection area on the retina. The PFOV has no physically measurable referent.
Attached Thumbnails
Click image for larger version

Name:	attachment.jpg
Views:	110
Size:	184.2 KB
ID:	276435  
__________________
Understanding optics is child's play by comparison with understanding child's play.

Last edited by elkcub : Saturday 7th August 2010 at 06:39.
elkcub is offline  
Reply With Quote
BF Supporter 2009 2010 2011 2012 2013 2014
Click here to Support BirdForum
Old Saturday 7th August 2010, 01:13   #13
Surveyor
The more I understand, the more I understand why I do not understand more!
 
Surveyor's Avatar

 
Join Date: Jan 2007
Location: Tennessee
Posts: 604
Thanks Ed;

Recently I have been doing some thinking and a little math concerning the eyes FOV, AFOV and exit pupil size about freedom of positions.

Your comments provide a little reinforcement and another avenue of possibilities to look into. I will get back to you when I firm up my thoughts and have some more data.

Have a good night.
__________________
RonE
Research is what I'm doing when I don't know what I'm doing.--Wernher Von Braun
Surveyor is offline  
Reply With Quote
Old Saturday 7th August 2010, 06:47   #14
looksharp65
Registered User
 
looksharp65's Avatar

 
Join Date: Feb 2010
Location: Varberg, Sweden
Posts: 1,603
elkcub,

thanks for your commendation. And also to all of you for your shared understanding of this tricky subject.
Surveyor, I will be delighted to know about your findings.
It is a not too bold assumption that the PFOV experience, though not measurable, is composed by the following properties:

1) A large AFOV
2) A long maximum eye-relief
3) A large first eyepiece lens ("ocular lens" ?)
4) Collapsed eyecups
5) A thin rim
And possibly also:
6) A fairly large exit pupil
7) Easy eye placement (less sensitive about IPD and actual eye-relief [distance from cornea to first lens])

-------------------------------

I don't expect anyone to have much interest in any of my personal binoculars, but today I have tested their focus speed. The results show that a mere measurement of the outer limits of the focus knob adds absolutely nothing to the understanding of the focus speed.

1) Minox BV 8x25 BRW. Totally 150 degrees from near point (1,8 m) to infinity. 90 degrees from 3m to infinity. (Undeniably a very fast focuser)
2) Vortex Fury 6.5x32. Totally 360 degrees from near point (1 m) to infinity. 100 degrees from 3 m to infinity.
3) Minox HG 8x33BR. Totally 300 degress from near point (1,3 m) to infinity. 150 degrees from 3 m to infinity.
4) Zeiss Classic 10x40. Totally 240 degrees from near point (cirka 4 m) to infinity. >> 3 m to infinity N/A, but the Minox HG is about 110 degrees in the same range.

Judging only by the focus knob range, the two fastest focusers would be the Minox 8x25 and the Zeiss. But the Zeiss needs more than 2 times more turning than the Minox HG in the 4m to infinity test. The Vortex would rank as a slower focuser than the Minox HG (that is considered a very fast focuser), but in the 3m to infity range the Vortex is 33 percent faster than the Minox.
Refocusing the Minox HG from 50 m to infinity will need about 25 degrees of turn, while the Vortex just needs a very minute touch. Probably none at all if my eyes were ten years younger or so.
__________________
http://en.wikipedia.org/wiki/Visby_lenses - The Viking optics
http://www.youtube.com/watch?v=LuBYpRkbzrs - The Viking War Cry

Last edited by looksharp65 : Saturday 7th August 2010 at 16:59.
looksharp65 is offline  
Reply With Quote
Old Saturday 7th August 2010, 18:01   #15
elkcub
Registered User
 
elkcub's Avatar

 
Join Date: Sep 2004
Location: Northern California
Posts: 2,947
Quote:
Originally Posted by Surveyor View Post
Thanks Ed;

Recently I have been doing some thinking and a little math concerning the eyes FOV, AFOV and exit pupil size about freedom of positions.

Your comments provide a little reinforcement and another avenue of possibilities to look into. I will get back to you when I firm up my thoughts and have some more data.

Have a good night.
Ron,

Sounds interesting, as is usual with your efforts.

Regards,
Ed
__________________
Understanding optics is child's play by comparison with understanding child's play.
elkcub is offline  
Reply With Quote
BF Supporter 2009 2010 2011 2012 2013 2014
Click here to Support BirdForum
Old Saturday 7th August 2010, 18:31   #16
henry link
Registered User

 
Join Date: Feb 2004
Location: north carolina
Posts: 3,143
I’ll throw in another idea to add to the mixture of possible causes for PFOV variations. This one, for lack of a better word, I would call “real”, instead of “perceived”.

Like others here I’ve noticed changes in the appearance or “feel” of the AFOV when I move my eye back and forth behind the eyepiece. Experiments with moving out-of-focus glitter points around in the field revealed that there is a “real” increase in illumination toward the field edge when the eye is closer to the eyepiece. There is typically a range of maybe 5-8mm between positioning the eye too close to the eyepiece so that kidney beaning sets in and too distant where the field stop becomes obstructed. The shape and size (surface area) of the off axis exit pupils are directly related to where in that range the eye is placed.

The greatest vignetting of off-axis exit pupils occurs when the eye is placed toward the back of the range and has the effect of slightly dimming the image at the field edge and also making lateral pupil positioning more critical. To my eye, in some cases the field only “feels” completely clear to the fieldstop when the eye is looking directly through the center. I suppose it’s what I would call a kind of “tunnel vision”. On the other hand the increased vignetting at that eye position can improve the appearance of edge sharpness by reducing astigmatism and field curvature because a large part of the objective is masked at the field edge as the exit pupil near the edge changes from a circle to a narrow slit.

I find that the eye position with the least vignetting is close to the eyepiece, just before kidney beaning starts. With the eye at that distance behind the eyepiece there’s more freedom for lateral pupil movement, by which I mean it’s possible to view the fieldstop clearly from a wider area of lateral pupil positions and the field edge looks a little brighter. On the other hand the relative lack of vignetting worsens the appearance of edge sharpness because there are larger doses of astigmatism and field curvature from the larger area of the objective illuminating the edge.

In spite of the loss of edge sharpness I prefer the “just before kidney beaning” eye position for the increased freedom of lateral pupil movement it allows. Many binoculars also appear a little brighter overall to me with this eye position, most likely because the exit pupil remains unobstructed over a wider area of the field.
henry link is offline  
Reply With Quote
Old Saturday 7th August 2010, 20:39   #17
Surveyor
The more I understand, the more I understand why I do not understand more!
 
Surveyor's Avatar

 
Join Date: Jan 2007
Location: Tennessee
Posts: 604
Looksharp65;

Concerning focus speed. In my testing, I always use diopters for reference (thanks to some of Henry Link’s posts) and found it saves considerable work and improves accuracy and understanding.

The only problem with the 3m to inf. test is that is does not account for power.

When testing I tape a millimeter scale to the focus knob and convert the binocular to a (very) poor mans dioptometer. Use the scale to measure the circumference of the knob and divide into 360 to get degrees per mm. It is a simple matter to take readings at known distances and convert to degrees per diopter or diopters per mm. All the binoculars I have tested are remarkably linear but I have never run into a geared or “dual speed” yet. The math is very simple; image space diopter=power^2/distance in meters.

With this in mind:

1) Minox BV 8x25 BRW. Totally 150 degrees from near point (1,8 m) to infinity. 90 degrees from 3m to infinity. (Undeniably a very fast focuser)

150/35.555=4.22*/d and 90/21.33=4.22*/d

2) Vortex Fury 6.5x32. Totally 360 degrees from near point (1 m) to infinity. 100 degrees from 3 m to infinity.

360/42.25=8.52*/d and 100/14.08=7.1*/d or avg.=7.8*/d

3) Minox HG 8x33BR. Totally 300 degress from near point (1,3 m) to infinity. 150 degrees from 3 m to infinity.

300/49.23=6.09*/d and 150/21.333=4.69*/d or avg. 5.4*/d

4) Zeiss Classic 10x40. Totally 240 degrees from near point (cirka 4 m) to infinity. >> 3 m to infinity N/A, but the Minox HG is about 110 degrees in the same range

240/9.6*/d for the Zeiss and 110/16=6.9*/d for 8x HG

If the angle of rotation was measured more accurately, I am sure the rates would be closer.

Going from memory the Nikon Monarch 8x36 is about 9*/d, the Promaster 8x43 ELX ED was about 22*/d, the ZR 7x36 ED2 was about 14.1*/d.

Attached is a picture of a tape attached to a binocular and a PDF you can print.
Attached Thumbnails
Click image for larger version

Name:	Paper Scale.jpg
Views:	130
Size:	107.5 KB
ID:	276644  
Attached Files
File Type: pdf Rulers_cm_narrow.pdf (43.4 KB, 218 views)
__________________
RonE
Research is what I'm doing when I don't know what I'm doing.--Wernher Von Braun
Surveyor is offline  
Reply With Quote
Old Saturday 7th August 2010, 22:24   #18
elkcub
Registered User
 
elkcub's Avatar

 
Join Date: Sep 2004
Location: Northern California
Posts: 2,947
Hello Henry,

Looksharp's comments that I resonate with pertain to a feeling that the FOV becomes bigger when using glasses. Not everyone may have this sensation, but I also sense an increase in image size. So, this may simply be the physical result of eyeglass magnification, which, in turn, does increase the AFOV as well. However, Looksharp's demonstration of rim thickness perceptual effects also bears a strong resemblance to what I experience, and also what I recall about various "windowing" effects on visual perception. Unfortunately, I can't find experiments that deal with scene superimposition or partial scene magnification. They might exit in the arena of helmet mounted displays, or artificial scene systems for aircraft simulators.

Ed

Quote:
The thing is, I use eyeglasses most of the time, and occasionally contacts.
When using glasses, and the eyecups are down, I have a feeling that the AFOV is greater. Of course it is not, but the "Wow!" comes when using glasses. When eyecups are extracted, and that wide black rim surrounds the image, I somehow get a feeling of tunnel vision. And reversely, when the eyecups are retracted so the rim appears thinner, the field seems to widen.

This leads me to thinking, if the ocular ends of the binocular's barrels are as thin as possible, and the exit pupil as large as possible, and the eye-relief generous, the "Wow!" experience would be granted. The "real AFOV" is easy to compute, but does it necessarily express what the perceived vision through a given binocular is like?
__________________
Understanding optics is child's play by comparison with understanding child's play.
elkcub is offline  
Reply With Quote
BF Supporter 2009 2010 2011 2012 2013 2014
Click here to Support BirdForum
Old Saturday 7th August 2010, 22:59   #19
looksharp65
Registered User
 
looksharp65's Avatar

 
Join Date: Feb 2010
Location: Varberg, Sweden
Posts: 1,603
elkcub, not all eyeglasses magnify the image (finally projected on the retina), only convex lenses for hyperopes do. As for myself, I am myopic, about -1,50 D which gives a very minute minification. I think you and me are strongly affected by an optical illusion (see link below)
Trying my Vortex (high eyepoint 22 mm) with the eyecups collapsed, moving the bin back and forth within the range limited by 1) blackout/kidneybeaning and 2) eyecup vignetting, the FOV feels larger when the bin is moved away from the eyes.
Also, this is where the rims appear the thinnest, and consequently, the lateral visual field is least affected. You have the Zeiss Classic 7x42 and know what I mean.
__________________
http://en.wikipedia.org/wiki/Visby_lenses - The Viking optics
http://www.youtube.com/watch?v=LuBYpRkbzrs - The Viking War Cry

Last edited by looksharp65 : Saturday 7th August 2010 at 23:27.
looksharp65 is offline  
Reply With Quote
Old Saturday 7th August 2010, 23:18   #20
looksharp65
Registered User
 
looksharp65's Avatar

 
Join Date: Feb 2010
Location: Varberg, Sweden
Posts: 1,603
henry link, Surveyor,

I am ever thankful for your scientific approach and concern in the two subjects.

Henry, I believe I am very "stiff" when looking through binoculars, that is, I center the subject I watch as near the optical axis as possible. Maybe this is the reason I can take advantage of really long eye relief (besides being able to use eyeglasses).

Surveyor, thank you for the pdf and the clarification. It is useful for determining the dioptric/linear speed of focus, in order to get undeniable and evidence-based information.
It seems all of my bins are fast focusers, right? You are right about the fact that the 3m to infinity measure does not count in the power of the bin in question.
But on the other hand, in real use, what actually matters is how fast and accurate you can refocus. Here, it is very striking how the Vortex is 33% faster, i.e. the knob only needs to be moved 67% of the Minox's, even though the latter has a "faster" focus knob.
Another very useful information is about the Promaster. I was having the idea of exchanging the Minox HG for a Hawke Frontier ED 8x42, but now it seems to me its focus speed is alarmingly slow.
__________________
http://en.wikipedia.org/wiki/Visby_lenses - The Viking optics
http://www.youtube.com/watch?v=LuBYpRkbzrs - The Viking War Cry

Last edited by looksharp65 : Saturday 7th August 2010 at 23:26.
looksharp65 is offline  
Reply With Quote
Old Saturday 7th August 2010, 23:24   #21
looksharp65
Registered User
 
looksharp65's Avatar

 
Join Date: Feb 2010
Location: Varberg, Sweden
Posts: 1,603
http://www.amazing-illusion.com/2008...-illusion.html
__________________
http://en.wikipedia.org/wiki/Visby_lenses - The Viking optics
http://www.youtube.com/watch?v=LuBYpRkbzrs - The Viking War Cry
looksharp65 is offline  
Reply With Quote
Old Sunday 8th August 2010, 22:27   #22
elkcub
Registered User
 
elkcub's Avatar

 
Join Date: Sep 2004
Location: Northern California
Posts: 2,947
Quote:
Originally Posted by looksharp65 View Post
elkcub, not all eyeglasses magnify the image (finally projected on the retina), only convex lenses for hyperopes do. As for myself, I am myopic, about -1,50 D which gives a very minute minification. I think you and me are strongly affected by an optical illusion (see link below)
Trying my Vortex (high eyepoint 22 mm) with the eyecups collapsed, moving the bin back and forth within the range limited by 1) blackout/kidneybeaning and 2) eyecup vignetting, the FOV feels larger when the bin is moved away from the eyes.
Also, this is where the rims appear the thinnest, and consequently, the lateral visual field is least affected. You have the Zeiss Classic 7x42 and know what I mean.
Looksharp,

Sorry to take this long to respond, but I was out buying a car and I had a few false starts composing this.

Yes, I would certainly agree that you being myopic handily discounts an explanation based on spectacle magnification. Forgive me for being pedantic, however, but in the area of perceptual psychology illusions are formally misperceptions, which are to be distinguished from the underlying perceptual processes that explain them. We don't generally reverse the process and use illusions to explain underlying visual-perceptual processes. (There are one or two notable exceptions when the illusion can be quantified. For example, Hemholtz' checkerboard illusion was quantified successfully and then used as a parameter to explain the "Globe Effect," which is yet another illusion (see http://www.holgermerlitz.de/globe/distortion.html).

I would say the perceptual phenomenon we experience with eyeglasses and binoculars is simply a manifestation of "size constancy," which is an ongoing perceptual process. It is not an illusion because there are no misperceptions involved. Objects either appear larger or smaller. This can be easily simulated, incidentally, by looking through a short tube at, let's say, a picture hung on the wall 15-20 ft. away. (A toilet paper tube works.) When the tube is put in front of your eye the picture immediately seems to become smaller, yet the retinal image remains the same either way. This is not an illusion, but rather the operation of the perceptual process known as size constancy. The mechanics are that the tube blocks off peripheral visual cues that the brain needs to estimate object distance, and, hence, object size. Under such conditions size perception becomes limited to the cue of retinal image size.

What I've increasingly come to understand is that the constancy mechanism even applies when the scene is differentially magnified. As mentioned in my earlier post, peripheral cues are still useful. Putting what you said above into this framework, when the rim appears to be thinnest note that it also least occludes peripheral cues.

It took me a while to get past your statement that you and I "are strongly affected by an optical illusion," as if we were unique in the world.

Actually, I believe that everyone experiences this perceptual effect. See below.

Ed
Attached Thumbnails
Click image for larger version

Name:	Size Constancy 2.jpg
Views:	93
Size:	156.6 KB
ID:	276934  
__________________
Understanding optics is child's play by comparison with understanding child's play.

Last edited by elkcub : Monday 9th August 2010 at 16:55.
elkcub is offline  
Reply With Quote
BF Supporter 2009 2010 2011 2012 2013 2014
Click here to Support BirdForum
Old Sunday 8th August 2010, 23:39   #23
looksharp65
Registered User
 
looksharp65's Avatar

 
Join Date: Feb 2010
Location: Varberg, Sweden
Posts: 1,603
Quote:
Originally Posted by elkcub View Post

It took me a while to get past your statement that you and I "are strongly affected by an optical illusion," as if we were unique in the world.

Actually, I believe that everyone experiences this perceptual effect. See below.

Ed
Sorry Ed, it's just that you, me and Kevin seem to agree more on this user-specific aspect on binocular use, as opposed to more scientific approaches. It would be very nice if a mathematical formula could be used to quantify this perceived property of binoculars.
However, I suppose that will not happen. I am very convinced that you are on the right track talking about size constancy, though measuring it might not be as easy as in your attached picture.
But it would be sad if this effect was put aside as mumbo-jumbo only because of its built-in inmeasurability (English is not my mother-tounge, apparently)

But besides the major difference between scientific approaches and user-perspective, I strongly suspect that the degree or level of misperception is not equal between individuals.

AC/A ratio (accomodative convergence per accomodative power) has a lot impact on the perceived size of the retinal image. By putting prisms in front of the eyes, they will be forced to adjust their position in order to avoid double-vision. The extra-ocular muscles then send signals to the brain how their respective tension is, and the brain computes these signals with respect to the simultaneous accommodation, and finally there will be a perceived change in object size.
Anyone who goes to an optometrist can ask for a prism flipper test. Prisms with their base towards your nose will allow the eyes to converge less, and the perceived object (text) size will appear larger.
Prism with the base temporally will force the eyes to converge more than they would without them, and the perceived object size will appear smaller.

But, as I wrote, the level of change is not equal to all individuals. Some will see a small perceived size change, while others will see an immense change.
The AC/A ratio plays a certain role in this.

Thank you for sharing your knowledge, I will get back tomorrow to read even more thoroughly. Now it is 1:40 AM here and the bed cries out for me.
__________________
http://en.wikipedia.org/wiki/Visby_lenses - The Viking optics
http://www.youtube.com/watch?v=LuBYpRkbzrs - The Viking War Cry
looksharp65 is offline  
Reply With Quote
Old Sunday 8th August 2010, 23:53   #24
looksharp65
Registered User
 
looksharp65's Avatar

 
Join Date: Feb 2010
Location: Varberg, Sweden
Posts: 1,603
I also have to add that spectacle lenses do have a real (measurable) impact on the retinal image size. But simultaneously, as the spectacles induce changes in the eyeballs' convergence, the perceived image size also becomes modified either towards even greater - or lesser - magnification/minification.
Luckily, the healthy human brain is very prone to adapt to the new circumstances, and this is why spectacles really work. If it wasn't, we might not even be helped by contact lenses, even though their impact on perceived image size generally is less than spectacles'.
__________________
http://en.wikipedia.org/wiki/Visby_lenses - The Viking optics
http://www.youtube.com/watch?v=LuBYpRkbzrs - The Viking War Cry
looksharp65 is offline  
Reply With Quote
Old Tuesday 10th August 2010, 00:57   #25
elkcub
Registered User
 
elkcub's Avatar

 
Join Date: Sep 2004
Location: Northern California
Posts: 2,947
Quote:
Originally Posted by looksharp65 View Post
Sorry Ed, it's just that you, me and Kevin seem to agree more on this user-specific aspect on binocular use, as opposed to more scientific approaches. It would be very nice if a mathematical formula could be used to quantify this perceived property of binoculars.
However, I suppose that will not happen. I am very convinced that you are on the right track talking about size constancy, though measuring it might not be as easy as in your attached picture.
But it would be sad if this effect was put aside as mumbo-jumbo only because of its built-in inmeasurability (English is not my mother-tounge, apparently)

But besides the major difference between scientific approaches and user-perspective, I strongly suspect that the degree or level of misperception is not equal between individuals.

AC/A ratio (accomodative convergence per accomodative power) has a lot impact on the perceived size of the retinal image. By putting prisms in front of the eyes, they will be forced to adjust their position in order to avoid double-vision. The extra-ocular muscles then send signals to the brain how their respective tension is, and the brain computes these signals with respect to the simultaneous accommodation, and finally there will be a perceived change in object size.
Anyone who goes to an optometrist can ask for a prism flipper test. Prisms with their base towards your nose will allow the eyes to converge less, and the perceived object (text) size will appear larger.
Prism with the base temporally will force the eyes to converge more than they would without them, and the perceived object size will appear smaller.

But, as I wrote, the level of change is not equal to all individuals. Some will see a small perceived size change, while others will see an immense change.
The AC/A ratio plays a certain role in this.

Thank you for sharing your knowledge, I will get back tomorrow to read even more thoroughly. Now it is 1:40 AM here and the bed cries out for me.
Looksharp, you're doing great expressing ideas in English, and certainly have introduced several that I hadn't considered. Most people, I suspect, are not familiar or interested in oculomotor systems and perception, so much of this is probably Greek (or might as well be).

I'm aware that prisms can be used to modify binocular convergence, but didn't know about changes in perceived image size. Of course it makes sense since size perception depends upon distance perception, and distance perception depends upon both accommodation and vergence cues. As a wild guess I would think the base-in prism effect is strongest for near targets, and that the observer probably adapts to it over time.

Are you by any chance an opthalmologist? I can't help but think about your Swedish countryman, the famous professor of opthalmology Allvar Gullstrand, who won the Nobel prize.
__________________
Understanding optics is child's play by comparison with understanding child's play.
elkcub is offline  
Reply With Quote
BF Supporter 2009 2010 2011 2012 2013 2014
Click here to Support BirdForum
Advertisement
Reply


Thread Tools
Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Similar Threads
Thread Thread Starter Forum Replies Last Post
swarovision focus speed falcondude Swarovski 4 Tuesday 19th January 2010 17:42
Conquest 8x40 focus speed? matt green Zeiss 7 Monday 30th March 2009 03:36
Sigma 300mm f2.8 + 1.4x auto focus speed? CCRII Sigma & Other Third Party Lenses 11 Monday 17th September 2007 23:54
Focus speed: Rebel XT vs 30D blackburnian Canon 1 Wednesday 1st March 2006 21:23
EL Focus Speed karmantra Swarovski 3 Tuesday 14th February 2006 21:44

{googleads}

Fatbirder's Top 1000 Birding Websites

Search the net with ask.com
Help support BirdForum
Ask.com and get

Page generated in 0.28602910 seconds with 37 queries
All times are GMT. The time now is 06:30.