[looksharp65]

Last summer I tried to approach the AFOV concept in a new way.
http://www.birdforum.net/showthread....64#post1892964

The result might be named "PFOV" for Perceived Field Of View. It has also been called transparency or walk-in.
To me, it's very obvious that AFOV does not tell everything about how the view through binoculars feel. Some of my ideas in that post are not correct, and I'm still trying to find out all the factors that promote the walk-in experience.

At present, I believe those are:

1) Sleek design of the housing, eyecups and barrels
2) Large ocular lenses + thin rim around them
3) Great eye relief
4) Eyecups collapsed
5) To certain extent, AFOV

In the next post, I've made a simple illustration.

[looksharp65]

The illustration is schematic. For example, the pair of eyes and the two barrels are made one.
The green, central part is what you see, the image and the apparent FOV.
The light green areas are what the human visual field perceives.
The grey area is what's beyond the human visual field (slightly beyond 180 degrees).
Finally, the red area is what is obscured by the field stop, the rims, the housing of the bnoculars and the hands. One might call this "negative PFOV".
If the hands are further away from the eyes they will obscure less of the human FOV.

# I is a non-wide angle binocular with the eyecup extended.
# II is the same sample with the eyecups collapsed.
# III is a wide angle binocular with the eyecup extended.
# IV is an equally wide angle bin with sleek eyecup design and eyecups collapsed.

The image portion of # III is greater than # I and the obscured part of the visual field is smaller.
Same thing happen between #II and # IV, but the sleek eyecups of # IV adds a few extra degrees of PFOV. If the eye relief allows holding the bins further away, the open area will increase, and the hands will get more out of the way.

As follows, a great AFOV is advantageous for the walk-in experience because it expands from the center towards the obscuration.
But if the outer edge of the obscuration/"negative PFOV" is further out, it will decrease the PFOV.
So, as little obscuration as possible is desired. IMHO.

[looksharp65]

Compact roof binoculars don't have great AFOV. If they had, they could also have a great PFOV if made with thin rims around the ocular lenses.
However, the fact that compact bins are small also mean that the hands some closer to the eyes and become another limiting factor of the PFOV.

[BrightIdea]

Looksharp, very interested in your various posts about this. I appreciate the diagrams and education.

In reviewing bins I have tried and liked vs those i've disliked, I notice I tend towards relatively large occular lense bin's, those with fairly large FOV, and ones that I can use with the eyecups in a lower or lowest position.

This could be the reason I prefer the 7x36 excursion over the technically much better Fury. More recently the theron vs sightron could be another example. The Theron has what I suspect is a larger Perception of FOV (I use them w/ eyecups down vs the sightron's larger cups slightly up) as well as a slightly larger actual FOV.

Your PFOV, coupled with a generous exit pupil, could very well be that non optical "ease of use" feature that I seem to put great emphasis on in my choices but have been unable to exactly pin down.

Thanks!

[looksharp65]

Originally Posted by BrightIdea

Looksharp, very interested in your various posts about this. I appreciate the diagrams and education.
...
Thanks!

You're welcome!

[FrankD]

I remember discussing this topic with you previously but not to any great extent.

Here is my take on it...it all comes down to how close you can get your eye to the surface of the ocular lens while still avoiding blackouts. This can be directly affected by some of the issues you mentioned...diameter of the eyecups, how far the ocular lens is recessed into the eyecups, etc....

To illustrate this situation I want to relate a recent experience I had with some of the classic porros I purchased. With some of them I cannot see the full field of view because the eye relief just isn't long enough for my facial dimensions...even with the metal eyecups removed. A few of them I can see close to the full field of view. So close that I don't really mind not being able to see all of it. A few others I can easily see the field stop so I am able to see the full field of view.

However, there are four specific models that, when I do remove the metal eyecups I can not only see the fieldstop but I also have much more of an expansive and immersive experience. I believe this is because I am able to get my eyes exceptionally close to the surface of the ocular while still avoiding blackouts. The reason for this is because the ocular surface is actually raised above the rest of the eyepiece assembly.

I will try to take a couple of pics of what I am referring to. I think this definitely is related to what you are searching for.

[looksharp65]

Originally Posted by FrankD

I remember discussing this topic with you previously but not to any great extent.

Here is my take on it...it all comes down to how close you can get your eye to the surface of the ocular lens while still avoiding blackouts. This can be directly affected by some of the issues you mentioned...diameter of the eyecups, how far the ocular lens is recessed into the eyecups, etc....

To illustrate this situation I want to relate a recent experience I had with some of the classic porros I purchased. With some of them I cannot see the full field of view because the eye relief just isn't long enough for my facial dimensions...even with the metal eyecups removed. A few of them I can see close to the full field of view. So close that I don't really mind not being able to see all of it. A few others I can easily see the field stop so I am able to see the full field of view.

However, there are four specific models that, when I do remove the metal eyecups I can not only see the fieldstop but I also have much more of an expansive and immersive experience. I believe this is because I am able to get my eyes exceptionally close to the surface of the ocular while still avoiding blackouts. The reason for this is because the ocular surface is actually raised above the rest of the eyepiece assembly.

I will try to take a couple of pics of what I am referring to. I think this definitely is related to what you are searching for.

Although related, what you say feels contra-intuitive for me.
This is how I see it:
The right image below shows a similar binocular as the left, but the eye relief is at its maximum.
The "free space" is undeniably greater. The obscuration caused by the outer dimensions of the binocular will be slightly smaller, as will the obscuration caused by your hands.

That said, the obscuration also will occupy a more central part of your visual field. Maybe you're more susceptible to that than to the very width of the obscuration.

Anyhow, big ocular lenses, great AFOV and thin rims still seem to benefit both of us.

Edit: The Nikon Wide MC 27x and the Wide DS 16x both have >70 degrees AFOV and a large ocular lens but unfortunately also a very wide rim.
However, the size of the ocular lens and the eye relief mean that the rim is out of the way, maybe similar to what you desire with binoculars.
It is hard to compare handheld binoculars and tripod-mounted angled spotting scopes when it comes to how we look through them, though.

//L

[FrankD]

LS,

I would agree about your reference to the Nikon widefield eyepieces. The more recent versions do provide that walk-in experience because of the greater eye relief and larger field of view...plus the flatter field.

Attached are the pics of what I was referencing earlier. Both of these models are 11 degree 7x35s though the Binolox (higher lens surface) gives slightly more of a walk-in experience.

[FrankD]

Slightly less

[FrankD]

More expansive....

[pshute]

Originally Posted by looksharp65

It is hard to compare handheld binoculars and tripod-mounted angled spotting scopes when it comes to how we look through them, though.//L

Ever tried photographing what you see? Something with a very small lens like a camera phone might be able to do it.

[elkcub]

Hi LS65,

There was more discussion of this phenomenon in a thread I started a week ago about the Swaro SLC 8x 42 HD. You might note the similarity of our diagrams: http://www.birdforum.net/showpost.ph...10&postcount=8, although I presented a binocular rather than cycloptic view so as to include monocular perspective cues and stereopsis.

In general, it seems to me that the longer the eye relief the further the observer's eyes must be placed from the ocular, which facilitates rays from unmagnified peripheral objects being imaged from either side (assuming they are not blocked intentionally by the eyecups). However, design factors generally dictate that long eye relief comes at the expense of either a narrow (true) field or a lower magnification.

The Swift 8.5x 44 HHS Audubon (narrow field) and the Zeiss 7x42 BGAT (lower magnification) are examples. Because of their long eye relief each is comfortable to use with eyeglasses, and IMO each presents a much reduced tunnel view using glasses.

Henry might wish to comment here, but it seems to be technically difficult, and hence expensive, to design binoculars with both a wide field and long eye relief. This is now a distinguishing characteristic of the new Swaro 8x 42 HD, and even more so the 8.5x 42 SV, — all of which justifies the cost for me.

Ed

[looksharp65]

Originally Posted by pshute

Ever tried photographing what you see? Something with a very small lens like a camera phone might be able to do it.

This thread is a continuation of the thread I linked to in the OP.

I have considered taking photos, but to succeed I have to use an extreme wide angle lens, and at these focal lengths we're talking about a fisheye lens.

Even after taking a usable photo, it has to be magnified to be larger than an ordinary computer screen.
Then it must be viewed at very short distance, maybe 0.1-0.2 meters.
I doubt this will help explaining the phenomenon. For a start, I direct you to the image in post #5 of that thread. I willl also add two other pictures soon.

[looksharp65]

Which image feels the most walk-in? Most people will find it's the one with the eyecups collapsed.
This illustration is very coarse. What I'm referring to is more the width and the placement of the black rim, or the size relation between the AFOV and the obscuration.

I'm planning to make a series of pictures intended to show what's happening when you approach the binoculars from a distance beyond the eye relief, gradually closer and finally too close, so that kidney beaning occurs.
With some binoculars, there is an ideal distance between the eyes and the ocular lenses where the black rim occupies the least possible part of the human FOV. Of course all this assumes the eyecups are collapsed.

Frank, is the black porro's eyepieces physically longer than the green one's?
I'm guessing both have short eye relief so when you can get really close to the ocular, the rim will come a lot further into the periphery of your visual field. This is not exactly what I'm talking of, since I'm dealing with AFOVs between 50 to 70 degrees and longer eye reliefs. Still I think what you have found is closely related to what I'm assessing here.


Ed, you're spot on and your diagrams are really cleverly thought out. Also the point about the Swaro having a very thin rim confirms my ideas about this. I'm forever thankful that you put your link here.
Provided that all binos were equally shaped in terms of size and intended hand placement, diagrams of your style would be all that's needed.
But, like I wrote in the OP, there's not only the width of the rim but also the external shape of the binoculars and where in the visual field the hands will be.
For example, My Zeiss 10x32 has a 69 degree AFOV at a shorter eye relief than my Vortex 6.5x32, but with the Zeiss, my hands are much closer to my eyes than with the Vortex. This makes the PFOV experience not too different.


//L

[elkcub]

//L,

For my own edification I set up a table to compare various bins in my collection that afford a full view with glasses. The order of merit column shows how I rank the five binoculars with regard to perceived "presence" and veridical stereoacuity (unmeasured), which is the ability to distinguish object distances in accordance with reality. The latter, IMO, is necessary for comfortable woodland birding, whereas the sensation of "being in the scene" is probably a perceptual correlate.

The annulus width (or contact ring width), is simply the eyepiece (eyecup) diameter minus the eyelens diameter. Except for the Swift 828, the AFOVs are right around 60º, but I find the Zeiss and Swaro are much superior to either Nikon, which I believe results from the field flattener interfering with my judgments of relative object distance. The eye relief is also greater than the Nikons', so it could be that as well, since the two variables are confounded as we say in the business.

In accord with your assessment, the annulus width is also perfectly correlated with the order of merit for the top four, again leaving the Swift aside because it's not matched for AFOV.

Ed
PS. Assuming my ordered judgments are 'correct,' for discussion purposes, note that we have a classic cause and effect problem, complicated by the fact that the independent variables are intercorrelated.

[looksharp65]

Thank you Ed!

The two most similar bins would be the Swaro SLC and the Nikon LX Lsince they share the AFOV. Like you say, the ranking is higher with greater eye relief and smaller annulus width.

//L

[looksharp65]

Sending pics showing
1) The very different grip of the Zeiss FL vs the Fury
2) What my right eye can see of my index finger. Because of the extreme wide angle needed I preferred to mix two pics to one. Forget about how the eyepieces look.

No doubt that the extremely sleek barrels of the Meostar 8x32 and the placement of the focusing knob is one of the secrets why it's considered having that extreme transparency. The hands come even further away from the eyes than the do with the Fury.
EDIT: I use an essentially symmetric grip with the Fury. With the Zeiss FL, I need to place the left hand in front of the right to get the right grip. Then it also gets out of the way and does not intrude into the left part of my visual field.

[elkcub]

LS65,

I hold all of my binoculars lower on the barrel and reach up and across with my index finger to focus. (The finger grooves on the Swaro almost force that.) When the ocular meets my glasses, therefore, all fingers are well out of the line of sight. The only situation where I might experience hand blockage is with compacts, but that's a narrow AFOV to begin with, and I don't use them much for birding.

Although interesting, I don't think it's a great idea to throw grip variations into the mix for understanding PFOV. But, that's just my opinion. Brock might have a different one. He reports having huge knuckles.

Sometimes I like to use a military grip, which also occludes side light effectively with glasses. Mostly I do that in glare situations.

Ed

[Renze de Vries]

[quote=looksharp65;2338286](...) having that extreme transparency./QUOTE]

This is an interesting thread, no doubt about it. I would gladly post some thoughts about it, were it not for the fact that I do have to finish some completely different work first. For the moment, just a short note on concepts used here to describe the phenomenon.

Transparency. Oh, oh, please let's try not to confuse things. I don’t like to see Transparency being used here as a synonym for PFoV. I think transparency refers to the relative absence of aberrations (of whatever kind) in the view.

Or are you saying that PFoV (as described in this thread) wil enhance transparency (as defined by me)?


Renze

[elkcub]

[quote=Renze de Vries;2338332]

Originally Posted by looksharp65

(...) having that extreme transparency./QUOTE]

This is an interesting thread, no doubt about it. I would gladly post some thoughts about it, were it not for the fact that I do have to finish some completely different work first. For the moment, just a short note on concepts used here to describe the phenomenon.

Transparency. Oh, oh, please let's try not to confuse things. I don’t like to see Transparency being used here as a synonym for PFoV. I think transparency refers to the relative absence of aberrations (of whatever kind) in the view.

Or are you saying that PFoV (as described in this thread) wil enhance transparency (as defined by me)?


Renze

It's always fun trying to herd us bino-cats. I don't use the word 'transparency' much in this (PFOV) context because I associate it primarily with the overall visual effect of reduced CA, which sharpens the image and eliminates a kind of gauzy haze. Henry has mentioned this sort of visual experience in the past regarding his Zeiss heavyweights. Oh, and you have a pair too.

Of the five bins listed in the table, I would rate the Swaro 8x HD as well above the others in transparency, but the SV models would also be outstanding. I would think that SA, coma, and astigmatism also need to be controlled to produce excellent transparency, but curvature of field and distortion probably not.

Ed

[looksharp65]

Renze,

I agree that transparency is not the perfect choice of words. But that's what I read in a review of the Meostar, the reviewer used that word to describe how the binoculars nearly seemed to disappear when held in front of the eyes.

Ed,

I believe you agree that the physical shape of the binoculars has an impact on how much of the visual field they obscure.
As I have tried to show, my hands must be in the equation because at least the right hand intrudes. It has to be right there in real use.
Admittedly, some binoculars permit a better grip like you described, but I doubt that could be done with the stubby Zeiss. Although slightly harder to quantify, it should be mentioned for binoculars like these that the hand may obscure the visual field to some degree. For others, that would be needless and thus easier to assess how the binocular itself promotes or obstructs the PFOV experience.

[looksharp65]

Assessing visual fields exactly without using a perimeter is nearly impossible. Doing it with a binocular in front of your eyes might be the recipe for epic fail.
Anyway, I've used a visual field map to make a rough estimation what happens in the visual field in exactly that situation.
The center part is the image, and it has an AFOV of about 60 degrees. Then comes the rim, which in this context must be of utmost importance. The size of the AFOV decides how far from center the fieldstop/inner edge of the black rim sits. The width of the rim decides how much of the periphery that can be seen.

The colored lines follow the visual field's lateral edges and are only there to enhance the readability of the map.
The black stripes indicate where the binocular intrudes into the visual field's medial parts so that the normal stereoscopic vision is lost. I've also marked where the image of the focusing knob is situated in the visual field. (the right one is for the left eye and vice versa).

This coarse map should correspond to #II or #IV of my drawings above but from the user's aspect. It is true that those drawings don't take stereo vision into account, but the visual field map should show that the superior (upper) and lateral (outer) parts of the visual field are the only of real interest here.

It shows we can divide PFOV into two subcategories:

1) The angular size of the AFOV in relation to the obscuration caused by the black rim.
Probably, a wide rim will not be as annoying if the AFOV is great as when AFOV is narrow.
2) The presence of peripheral visual impressions.
The distance needed to produce an unobstructed image (the eye relief) is important here, where a greater eye relief allows more peripheral vision.
Physical shape of the binoculars, eyecup features, hand placement et cetera may also contribute.

[looksharp65]

Originally Posted by elkcub

Brock might have a different one. He reports having huge knuckles.

Ed

Sure that ain't the porro prism housings?

[elkcub]

Originally Posted by looksharp65

...
This coarse map should correspond to #II or #IV of my drawings above but from the user's aspect. It is true that those drawings don't take stereo vision into account, but the visual field map should show that the superior (upper) and lateral (outer) parts of the visual field are the only of real interest here.

It shows we can divide PFOV into two subcategories:

1) The angular size of the AFOV in relation to the obscuration caused by the black rim.
Probably, a wide rim will not be as annoying if the AFOV is great as when AFOV is narrow.
2) The presence of peripheral visual impressions.
The distance needed to produce an unobstructed image (the eye relief) is important here, where a greater eye relief allows more peripheral vision.
Physical shape of the binoculars, eyecup features, hand placement et cetera may also contribute.

LS65,

Very nice! A portion of the focus wheel does lie within the field of vision of each eye, and placed more or less where you describe it. One has only to wink alternately to see it. But, like the nose, the obscuration disappears using both eyes, and probably for the same reason: the brain.

Your physical division of the PFOV summarizes our discussion nicely. A rim of any width probably is less annoying as AFOV increases.

Ed

[elkcub]

Originally Posted by looksharp65

Sure that ain't the porro prism housings?

Nah, he said he saw hair on them.

Ed