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Edge to edge sharpness - a misleading criterion? (1 Viewer)

I find this confusing. Look through a tunnel with sharp edges, or looking through a larger tunnel with fuzze edges. Is not the important thing how large a area things are sharp in? Centering on something is easy when it is still but most things I look at are moving.
 
La Mer said:
I have no experience with alpha binos (alas!), but still I'd like to ask my favorite question here: Is it that simple (to center your binos on an object)? I am well aware that our eyes don't give a sharp image even a few degrees away from the center, but then you can obviously move your eyes much faster than your binos. Thus, when a bird is moving to and fro or is moving along fast and you have problems keeping it in your field of fiew at all, you'll obviously use the field to the very edges, whether you want to or not. This could be a possible explanation why edge-sharpness might be important. But as I said, I'm not talking from experience, so I really just wonder. - However, I'd definitely prefer an 8 degree bino with blurred edges to one that has only 7 degrees with sharp edges.



I also quite like your approach, Florian: Zen and the Art of using Binos (without the hated -Ray this time ....). So, even if you still don't know why you are posting here, others may value your posts.

Elu

PS: WJC, you are certainly not on my ignore-list (nor is anyone else), so I hope to see a lot of your expert opinions in the future too.
Click to expand...

I have never had a problem centering on birds. Rarely am I closer than 60 feet from them so theres plenty of space for them to move. But I am as likely to be watching other wee beasties as I am watching birds.
 
With my Zen ED2 I have to really hold them tight against my glasses to keep from loosing some FOV. When it happens the actual FOV is still huge, but psychologically, seeing the slight dark ring around the image makes the view seem a bit restrictive.

La Mer said:
However, I'd definitely prefer an 8 degree bino with blurred edges to one that has only 7 degrees with sharp edges.
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Various views ....

There's an interesting contrast between what SailorDoug and what perterra says. I suppose it depends much on the birds you are watching and also on the landscape. If it's open and wide, it may not be difficult following most birds and centering them. If you are in dense forest or between reeds (like I am rather often) and you suddenly have a kingfisher flashing up in front of you, soaring along that canal, or some reed warbler flitting to and fro 3 meters ahead of you, you are glad of every half degree field of view, whether sharp or not. As long as the bird is within the FOV, you can always try to center, but when it's out, we all know how hard it is to find the beast again without taking the binos off. So, that's the reason why even a blurry edge is useful, I'd say.

This leads me to the next point - BH46118's statement about human vision being sharp from edge to edge. What do you refer to? Look at a word on your monitor, then move the center of your vision 1 degree away (about the width of your index finger with outstretched arm) - now, can you still read that word? Probably not, and certainly not if you move it 2 or 3 degrees further away. However, our vision has a FOV of about 180 degrees. That also shows that blurred parts of a FOV are not at all useless - they still enable you to see movement, and then you can center (which, however, is much easier with your eyes than with binos).

Therefore, my ideal bino would be such: Give me a reasonably wide sweet spot, and then give me an unreasonably wide total FOV, however poor the edge performance may be. But I fear that especially the alpha manufacturers will not do that, because then the reviews would complain about .... blurry edges!

Elu
 
La Mer said:
There's an interesting contrast between what SailorDoug and what perterra says. I suppose it depends much on the birds you are watching and also on the landscape. If it's open and wide, it may not be difficult following most birds and centering them. If you are in dense forest or between reeds (like I am rather often) and you suddenly have a kingfisher flashing up in front of you, soaring along that canal, or some reed warbler flitting to and fro 3 meters ahead of you, you are glad of every half degree field of view, whether sharp or not. As long as the bird is within the FOV, you can always try to center, but when it's out, we all know how hard it is to find the beast again without taking the binos off. So, that's the reason why even a blurry edge is useful, I'd say.

This leads me to the next point - BH46118's statement about human vision being sharp from edge to edge. What do you refer to? Look at a word on your monitor, then move the center of your vision 1 degree away (about the width of your index finger with outstretched arm) - now, can you still read that word? Probably not, and certainly not if you move it 2 or 3 degrees further away. However, our vision has a FOV of about 180 degrees. That also shows that blurred parts of a FOV are not at all useless - they still enable you to see movement, and then you can center (which, however, is much easier with your eyes than with binos).

Therefore, my ideal bino would be such: Give me a reasonably wide sweet spot, and then give me an unreasonably wide total FOV, however poor the edge performance may be. But I fear that especially the alpha manufacturers will not do that, because then the reviews would complain about .... blurry edges!

Elu
Click to expand...

I agree with everything you said.
 
Certainly the AFOV has to come into the equation when considering edge sharpness. Few would be happy with a tack sharp to the edge 50° AFOV bin, and similarly few would be happy with an 80° AFOV bin where half that field was an uninformative blur.

Ed has presented information before showing that normal ordinary field of vision for humans is ~60° (of course the ultra-sharp in focus bit defined by the fovea is much less than that). This seems to correlate to my experience where I find anything greatly less than 60° AFOV to be decidedly port-hole like, and not to my liking at all. In fact I prefer well corrected 65° AFOV or over, to start to give that feeling of the 'walk-in' view.

I personally think that 70° AFOV is where it is at, although as Bill, (Dale on another thread - the logic of which went completely over Brock's head - in one ear and out the other - without pause to sink in and change his pre-determined reply! :), and many others with a knowledge of optics design have said, the complexities, compromises, and hurdles faced when stretching from that 50° AFOV mark out towards 70° become mind boggling, and very very difficult to correct all the aberrations in a practical (weight, size, cost wise) device.

The Swift Audubon 8.5x44 ED has a 69.7° AFOV - pretty darn good - but does exhibit some field curvature softness, among others, in the outer field. So much so that even someone in their 30's with a goodly amount of accommodation still left won't be able to contort the eyeball into giving a sharp edge to edge view. Still that expansive AFOV is quite nice.

A lot of my 'birding' is done by detection of movement - in the outer field that doesn't need tack sharpness, but enough to be able to detect movement. I didn't think that the Swift sufferred that much (given it's $2.5K view for less than 1/5 that cost! :), until one day when I was lakeside and could hear Rainbow Bee-Eaters ......... low and behold upon recentering the bin, there had been one perched on a dead branch, sitting reasonably still apart from the beak, in that outer 20% of the field --- didn't notice him at all in the blurred Swift edge !!! Now I want 'enough' sharpness in that outer field to be able to detect and process stationary targets .....

I don't have to have the field tack sharp to the edge (especially at 70° AFOV -which is impossible to look at from the fixed central gaze anyway - and somewhat risky too - I believe if the wind changes while you're doing that, then you'll stay cross-eyed like that forever - at least that's what my dad told me! |:p| :), just sharp enough to reveal stationary detail, BUT I also want no 'mustachio' rings of softness, or RB phenomena for ordinary folk (say k~0.7, no more) - can't be that hard really can it?!


Chosun :gh:
 
In most situations, I'm perfectly fine with a field about 50% sharp, and if the sharpness only gradually fades to a blur, then so much the better. Having said that, it's very pleasurable to use a binocular like the SE, with its expansive sweet spot and only slightly soft edges. I also prefer a flat field for stargazing.
 
If my eyes are focussed on the target Bird then the edges soft or sharp are pretty much ignored by my brain, however when taking in perhaps a flock of more distant targets or perhaps a general sweep of countryside that`s when I notice the fuzziness if its there.

I agree with CJ on 70* f`sov, and the EII still provides the most absorbing view I`v yet tried.
 
There is ambiguity in the phrase "edge to edge sharpness" which I suspect confuses a number of people. I suppose it's mostly used to describe flat field designs, so at any given distance the full width of the view is in focus. However no view is entirely flat and to varying degrees the edges focus at a closer point than the middle and it relies on the users focal accommodation to do the rest of the work. Fine for youngsters but a lot of us struggle. In fact I find field curvature is frequently a positive attribute. I've found I rarely look directly at the horizontal edges but frequently do at the bottom. Having stuff outside the centre focus closer is very useful, particularly when closer accounts for pretty much all the foreground of the view. Giving up a bit of focal sharpness at the sides of the view in return for a sharp perceived increased DOF works for me. So edge to edge sharpness with field curvature is also good.

So I like sharp edged, curved field designs. I also like edge to edge flat designs for other situations. No real hard and fast rules here but generally low powered with field curvature and higher powered flat views seem to work for me.

As long as the edges are sharp then I find a 55* AFOV perfectly acceptable in either style, but yes, wider is nicer and I'd accept the point a number have made about peripheral vision. In addition to these two design styles there are a mass of binoculars on the market with intermediate designs, lowish field curvature and depending on the choice of field stop, frequently fuzzy edges. As long as they remain sharp to around 55* AFOV then I'm reasonably content with the compromise, just not as useful as having a choice.

David
 
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Chosun Juan said:
Certainly the AFOV has to come into the equation when considering edge sharpness. Few would be happy with a tack sharp to the edge 50° AFOV bin, and similarly few would be happy with an 80° AFOV bin where half that field was an uninformative blur.

Ed has presented information before showing that normal ordinary field of vision for humans is ~60° (of course the ultra-sharp in focus bit defined by the fovea is much less than that). This seems to correlate to my experience where I find anything greatly less than 60° AFOV to be decidedly port-hole like, and not to my liking at all. In fact I prefer well corrected 65° AFOV or over, to start to give that feeling of the 'walk-in' view.

I personally think that 70° AFOV is where it is at, although as Bill, (Dale on another thread - the logic of which went completely over Brock's head - in one ear and out the other - without pause to sink in and change his pre-determined reply! :), and many others with a knowledge of optics design have said, the complexities, compromises, and hurdles faced when stretching from that 50° AFOV mark out towards 70° become mind boggling, and very very difficult to correct all the aberrations in a practical (weight, size, cost wise) device.

The Swift Audubon 8.5x44 ED has a 69.7° AFOV - pretty darn good - but does exhibit some field curvature softness, among others, in the outer field. So much so that even someone in their 30's with a goodly amount of accommodation still left won't be able to contort the eyeball into giving a sharp edge to edge view. Still that expansive AFOV is quite nice.

A lot of my 'birding' is done by detection of movement - in the outer field that doesn't need tack sharpness, but enough to be able to detect movement. I didn't think that the Swift sufferred that much (given it's $2.5K view for less than 1/5 that cost! :), until one day when I was lakeside and could hear Rainbow Bee-Eaters ......... low and behold upon recentering the bin, there had been one perched on a dead branch, sitting reasonably still apart from the beak, in that outer 20% of the field --- didn't notice him at all in the blurred Swift edge !!! Now I want 'enough' sharpness in that outer field to be able to detect and process stationary targets .....

I don't have to have the field tack sharp to the edge (especially at 70° AFOV -which is impossible to look at from the fixed central gaze anyway - and somewhat risky too - I believe if the wind changes while you're doing that, then you'll stay cross-eyed like that forever - at least that's what my dad told me! |:p| :), just sharp enough to reveal stationary detail, BUT I also want no 'mustachio' rings of softness, or RB phenomena for ordinary folk (say k~0.7, no more) - can't be that hard really can it?!


Chosun :gh:
Click to expand...

Despite competition from others, this is, as far as I'm concerned, the best post yet on the topic being both humorous and informative (plus, by entirely resisting the temptation to snipe at others, a pleasure to read). Thanks! Personally I find the eyeball contortions required to critically check the degree of softness at the edge of a field so uncomfortable that I rather doubt tack a tack sharp view to the edge would be much use to me.
 
My statement was vague and I'm sure technically incorrect. I meant that when I roll my eyes around I see a clear view wherever I look. That is the only way I know to see the edge of the FOV of an optic, to roll my eyes to the side to look at it. I'm sure even the best human eye has distortion and aberration, unfortunately I can't buy a new pair to get rid of my floaters, increases internal pressure, and need for glasses. My Zen ED 2 and SV are polar opposites in regards to edge sharpness and field curvature, but I still enjoy the Zen. I would be lying If I said I don't like the edge view on the SV better though.


La Mer said:
This leads me to the next point - BH46118's statement about human vision being sharp from edge to edge. What do you refer to? Look at a word on your monitor, then move the center of your vision 1 degree away (about the width of your index finger with outstretched arm) - now, can you still read that word? Probably not, and certainly not if you move it 2 or 3 degrees further away. However, our vision has a FOV of about 180 degrees. That also shows that blurred parts of a FOV are not at all useless - they still enable you to see movement, and then you can center (which, however, is much easier with your eyes than with binos).
Click to expand...
 
John Cantelo said:
Despite competition from others, this is, as far as I'm concerned, the best post yet on the topic being both humorous and informative (plus, by entirely resisting the temptation to snipe at others, a pleasure to read). Thanks! Personally I find the eyeball contortions required to critically check the degree of softness at the edge of a field so uncomfortable that I rather doubt tack a tack sharp view to the edge would be much use to me.
Click to expand...

I dont know, seems a slight snipe at Brockles. :-O
 
Incorrect but interesting

bh46118 said:
My statement was vague and I'm sure technically incorrect. I meant that when I roll my eyes around I see a clear view wherever I look. That is the only way I know to see the edge of the FOV of an optic, to roll my eyes to the side to look at it.
Click to expand...

Though technically incorrect, I now find the remark rather interesting. The point of it really is that we move our eyes all the time without noticing it at all. I don't just mean when looking up, down, sidewards - but also when our vision is apparently centered, our eyes are actually scanning the image continually (without us performing any conscious eye-movement). However, the movements cover only a few minutes of arc, whereas the spot of highest visual acuity covers about 2 degrees.

https://en.wikipedia.org/wiki/Eye_movement

This would suggest that unconscious eye movement is always within the sweet spot of a bino, so that edge sharpness is needed only for the (theoretically!) conscious eye movement.

Elu
 
La Mer said:
.....This would suggest that unconscious eye movement is always within the sweet spot of a bino, so that edge sharpness is needed only for the (theoretically!) conscious eye movement.

Elu
Click to expand...

Or ..... peripheral vision! :t:

Agree with the rest of what you have said Elu.

I think one particular application where sharpness to the edge comes into its own is in watching two or more circling raptors. They will tend to position themselves on the opposite side of a thermal, and so present themselves at either edge of the FOV. I have found that this still needs a minimum FOV of 6.5° + for our locals ..... hence I am really looking forward to laying eyes on the 120m FOV 10x42 SF ....... *grin* :t:


Chosun :gh:
 
There's three factors involved, near as I can tell.

1) Can you perceive sharp edges? Yes, it's there in your peripheral vision, and the sharper the better. When I switch from the 8x32 SV to the 8x32 FL the soft edges kind of slap me in the face.

2) Can you look directly at sharper edges? Mostly no. Everything blacks out before you get there, without silly and heroic efforts anyway. Which is why the "Absam ring" is such a dead-end.

3) The eyepiece makes a big difference. The bigger the "roam around" view is the more sharp edges matter. I don't care too much for the edges of the 8x32 FL because a) they're fuzzy, and b) it blacks out real fast trying to get there. Not so the 8x32 SV. It's roomy and sharp, and I can look over flocks if I want to, whales if I want to. See Lee's comments above.

The 8.5x SV is even better but the FOV is less.

Is the whole thing the "be all and end all"? Not really, just my two cents. But from here on out I probably wouldn't buy an alpha that wasn't flat field.

I'm looking forward to seeing the Zeiss SF. I assume they dissected the SV eyepiece to see how that marvel works.

Mark
 
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Edge to edge sharpness isn't mandatory for the enjoyment of an optic, but to my eyes it's an enhancement even if it's in the outer periphery. I believe optics are a little like high end audio. The theory is that an audio system that poorly resolves spatial and musical information causes the brain to try and fill in the missing blanks thus causing listener fatigue. The more elements of reality an optic is able to resolve in a natural way, the less your brain has to work to fill in the missing information, which in turn has a calming effect and makes for fatigue free viewing. Does that make any sense ?|=)|
 
Kammerdiner said:
1) Can you perceive sharp edges? Yes, it's there in your peripheral vision, and the sharper the better. When I switch from the 8x32 SV to the 8x32 FL the soft edges kind of slap me in the face
Mark
Click to expand...
Can some people perceive sharp edges? Yes it is there in their peripheral vision, and for them, the sharper the better. When one of them switches from the 8x32 SV to the 8x32 FL, the soft edges kind of slap them in the face. Mark is one of them...nothing at all wrong with that to be sure ;). However, they would be better served to figure out that there in fact are others (how many others as a percentage of the population I have no idea) that do not see things the same way.

Points two and three I agree with.

Different binoculars are just that...,different. Same with eyes of binocular users...different. Same with the mind sets of the binocular user...different. Different, not better or worse, just different. That is why we need different binoculars.
 
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Steve C said:
Can some people perceive sharp edges? Yes it is there in their peripheral vision, and for them, the sharper the better. When one of them switches from the 8x32 SV to the 8x32 FL, the soft edges kind of slap them in the face. Mark is one of them...nothing at all wrong with that to be sure ;). However, they would be better served to figure out that there in fact are others (how many others as a percentage of the population I have no idea) that do not see things the same way.

Points two and three I agree with.

Different binoculars are just that...,different. Same with eyes of binocular users...different. Same with the mind sets of the binocular user...different. Different, not better or worse, just different. That is why we need different binoculars.
Click to expand...

It seems lately, no matter what I say, it is taken wrong. So I will apologize in advance. In the last few posts on this thread, we see some folks praising their ever-sharp peripheral vision. The following is from the first post on the Field Curvature thread:

"Printout a line of gibberish text—about 28-point—stretching across the page. Now, tape it to the wall, 3 feet in front of you. Then CONCENTRATE on one of the letters near the center of the text.

"Now, while still CONCENTRATING on that ONE letter, what is the 10th letter on the right, or 8th letter on the left? They’re close together. But, if you are really concentrating on that first letter … you CAN’T make out the others. If you can, the Optical Sciences Center in Tucson or Rochester will want to talk to you."

I left that as an invited test for ALL to see and evaluate.

What I must humbly and grovelling ask is: who is it really that can do what the rest of America can't?

If a person owns a good bino, and looks at the edge of the field, for even a tiny fraction of a second, they can take advantage of the bino's good field and think it's their peripheral vision. But having a sharp peripheral vision is not a happening thing.

"Hell, I can see just as good with the Jason Permafocuses, as I can with any of them [sic] expensive binoculars in that case." (Zeiss, Leica, Swarovski, Nikon, Kowa, etc.)-- A customer at Captain's Nautical.

Was he right?

Bill
 
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