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Edge to edge sharpness - a misleading criterion?

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Old Thursday 25th September 2014, 13:57   #1
John Cantelo
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Edge to edge sharpness - a misleading criterion?

I'll nail my flag to the mast straight off – I'm a birder who's used binoculars for over 50 years, but I'm not an optics nut or engineer. The technicalities of optical design leave me cold and only impinge on my awareness when I look through a product. So I'm prepared to be shot down in flames for my lack of technical nous.

What I do wonder about is what seems to me a fairly recent stress on 'edge to edge sharpness' as an important factor in selecting binoculars. Obviously nobody wants binoculars where sharpness falls off very sharply and the sweet spot is tiny, but I don't see instruments like this on the market. It's usually a matter of 10-15%.

In all my years of using bins I've always centred my optics on the subject of interest so by and large if the outer 10% of the view isn't quite so sharp then it really doesn't matter. What often does matter though, is to have a generous field of view so that I see birds at the periphery of my view or more easily locate and track birds in foliage etc. An instrument with sparkling edge to edge sharpness may seem better than one with a less good view for the outer 10%, but in reality if it has a field of view of, say, 140m, in practical terms I suspect I'd find it less useful than binoculars with a 150m FoV even if only 135m of that view is razor sharp. That extra 10m of view will allow me to detect a bird otherwise unseen and I'll instantly swing my optics round to get that premier view. So is a stress on edge to edge sharpness, particularly without reference to FoV, misleading?
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Old Thursday 25th September 2014, 16:07   #2
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I did`nt use to think it important, however I`v used my SE as my primary Birding bin for 18 months now and really notice the lack of edge sharpness in bins without it. I think nearly all SV owners will tell you its hard to give up on once accustomed.
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Old Thursday 25th September 2014, 16:14   #3
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That is good reasoning John.

Often these binoculars can have their edges dialed into focus. If you are sharply focused on a bird inside of a tree's foliage the entire view can also appear to be in focus because part of that foliage can also be within the area of the binoculars edge sharpness. This is particularly useful in close up situations where depth of field is important. It could be of help in following the bird through the tree. Birds do not stay within a binoculars flat plane of focus in close up situations.

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Old Thursday 25th September 2014, 16:56   #4
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Originally Posted by John Cantelo View Post

So is a stress on edge to edge sharpness, particularly without reference to FoV, misleading?
In a word John, Yes! Although as soon as one has said this there looms the prospect of defining how sharp or unsharp the area out of the 'sweet spot' is acceptable.

I am a target-centering observer like you and only stumbled into the realisation of how important sharp edges can be when whale watching on Skye this July. With the whales only being visible for a very few seconds it was necessary to decide very quickly whether that small shadow out at the periphery of view was the beginning of a whale-back surfacing or not. A wide FOV and better edge sharpness would have been appreciated.

And since looking through Zeiss's new SF I have come to realise how this extra dimension to the view can be important, and, yes, I have to apologise to all of those EL SV owners who already knew this and whose opinion on the matter I have not taken seriously enough.

But you are correct, its no use making comments about sweet spots and edge sharpness unless you put those into context by specifying the FOV.
For example, in comparing the edge sharpness of SF 8x42 with EL SV 8.5x42 one should take into account the FOV of 148m of the former vs the 133m of the latter and in technical terms one should also bear in mind the extra 0.5x magnification of the Swaro.

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Old Thursday 25th September 2014, 17:09   #5
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Originally Posted by John Cantelo View Post
I'll nail my flag to the mast straight off – I'm a birder who's used binoculars for over 50 years, but I'm not an optics nut or engineer. The technicalities of optical design leave me cold and only impinge on my awareness when I look through a product. So I'm prepared to be shot down in flames for my lack of technical nous.

What I do wonder about is what seems to me a fairly recent stress on 'edge to edge sharpness' as an important factor in selecting binoculars. Obviously nobody wants binoculars where sharpness falls off very sharply and the sweet spot is tiny, but I don't see instruments like this on the market. It's usually a matter of 10-15%.

In all my years of using bins I've always centred my optics on the subject of interest so by and large if the outer 10% of the view isn't quite so sharp then it really doesn't matter. What often does matter though, is to have a generous field of view so that I see birds at the periphery of my view or more easily locate and track birds in foliage etc. An instrument with sparkling edge to edge sharpness may seem better than one with a less good view for the outer 10%, but in reality if it has a field of view of, say, 140m, in practical terms I suspect I'd find it less useful than binoculars with a 150m FoV even if only 135m of that view is razor sharp. That extra 10m of view will allow me to detect a bird otherwise unseen and I'll instantly swing my optics round to get that premier view. So is a stress on edge to edge sharpness, particularly without reference to FoV, misleading?

I dont think edge to edge sharpness is as important as wide field of view. I always center on my target. It might be more important in a telescope but for something as easy to move as a binocular it's not an issue for me. It's nice to see edge to edge sharpness, but not a must have for me.
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Old Thursday 25th September 2014, 17:29   #6
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I dont think edge to edge sharpness is as important as wide field of view. I always center on my target. It might be more important in a telescope but for something as easy to move as a binocular it's not an issue for me. It's nice to see edge to edge sharpness, but not a must have for me.
There you go with that logic stuff, again.

Wish me luck. I'm getting ready to go out and spend $150 to get a new headlamp put in. I took my Equinox to two auto shops, yesterday, and one couldn't do it and the other wanted me to wait 24 hours!

'Remember when changing a headlamp took loosening 3 screws and then tightening them again!?

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Old Thursday 25th September 2014, 17:31   #7
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I'll nail my flag to the mast straight off – I'm a birder who's used binoculars for over 50 years, but I'm not an optics nut or engineer. The technicalities of optical design leave me cold and only impinge on my awareness when I look through a product. So I'm prepared to be shot down in flames for my lack of technical nous.

What I do wonder about is what seems to me a fairly recent stress on 'edge to edge sharpness' as an important factor in selecting binoculars. Obviously nobody wants binoculars where sharpness falls off very sharply and the sweet spot is tiny, but I don't see instruments like this on the market. It's usually a matter of 10-15%.

In all my years of using bins I've always centred my optics on the subject of interest so by and large if the outer 10% of the view isn't quite so sharp then it really doesn't matter. What often does matter though, is to have a generous field of view so that I see birds at the periphery of my view or more easily locate and track birds in foliage etc. An instrument with sparkling edge to edge sharpness may seem better than one with a less good view for the outer 10%, but in reality if it has a field of view of, say, 140m, in practical terms I suspect I'd find it less useful than binoculars with a 150m FoV even if only 135m of that view is razor sharp. That extra 10m of view will allow me to detect a bird otherwise unseen and I'll instantly swing my optics round to get that premier view. So is a stress on edge to edge sharpness, particularly without reference to FoV, misleading?
“I'll nail my flag to the mast straight off . . .”

Sometimes, when I do that, I get yelled at. But, I figure that your work is much more succinct if you cut all the sweet, politically correct stuff. (Bet you wish you could have done that as a teacher, especially a high school teacher. [My wife has gone from teaching in an affluent area to one in which the kids could bite the tires off a moving cop car.]

You bring up a very good point. But, that’s because you’re into BIRDS; so many are into BINOCULARS. The needs of the two groups vary by a large margin.

In years of repairing and selling binoculars, I’ve heard all manner of remedies for the problem … which are not! Some people dwell on the DRILL and not the HOLE it was designed to make—supposedly the reason they bought the drill, in the first place. Then, too, the arena of discussion is wide and can create some lively discussion.

Fact #1—The problem is curvature of field.
Fact #2—Some people go mad because of it; others can’t be MADE to see it.
Fact #3—Some folks brag about the “great” bino they just bought for less than dining out. And then,
Fact #4—Complain about all the properties that don’t resemble those of Zeiss, Leica, or Swarovski.

Torview and I don’t have to worry about the problem; we use the Nikon 8x32 SE—primarily. But I have had many days of enjoyment with some of the cheap binos I have lying around the house. I like my late 50s/early 60s Jason Statesman, and you don’t get much lower on the food chain. It has a very wide field of view. The outer portion would cause some to have fits. But, I understand its undesirable qualities and focus on its positive qualities. The enjoyment SHOULD be in the view.

Those who insist on buying cheap binos (or truly CAN’T afford better) should consider buying an instrument with a smaller FOV. The work lens designers have to do increases exponentially as the size of the FOV increases.

In REAL optics (as opposed to the ethereal optics of conversation), you can’t come close to having it all without spending more money.

In my last hurrah, the Celestron Ultima and the Swift Ultra Lite (both the same on the inside) were good examples. The fields of view were restricted in size, but that which was left would rival some of the very best binoculars!

“There are good optics, and there are cheap optics. But, there are no GOOD/CHEAP optics!” —Leif Robinson, former editor-in-chief, Sky & Telescope

Cheers,

Bill
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Old Thursday 25th September 2014, 17:37   #8
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It's not the first time this issue is raised here, and what I've learn from the many discussions is: those that have binoculars with edges not so sharp, think sharp edges are not important; and those that have binoculars with sharp edges think it is important.
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Old Thursday 25th September 2014, 17:46   #9
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It's not the first time this issue is raised here, and what I've learn from the many discussions is: those that have binoculars with edges not so sharp, think sharp edges are not important; and those that have binoculars with sharp edges think it is important.
And will be raised again, and again, and again, as there will be a never-ending line of new members who are not aware of the topic being raised 8,417 times in the last . . . year.

Que Sera, Sera,

Speaking of which, I'm going Mexican for lunch!

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Old Thursday 25th September 2014, 18:08   #10
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I dont think edge to edge sharpness is as important as wide field of view.
As one who uses binoculars primarily for hunting I value both highly.

Sad to say I've hit the ignore button for someone for the first time since joining this forum ; three posts in one thread on the same old story. It's so boring !
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Old Thursday 25th September 2014, 18:30   #11
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I did`nt use to think it important, however I`v used my SE as my primary Birding bin for 18 months now and really notice the lack of edge sharpness in bins without it. I think nearly all SV owners will tell you its hard to give up on once accustomed.
My wife and I used 8X32 SE's for many years. I also owned a 7X42 Ultravid (a stellar bin in so many ways). After nearly ten years the soft edges of the Ultravid became too much of a distraction. I wanted the "SE view" in a rugged waterproof binocular so the Leica went to a relative and I went shopping.

I looked at Swarovisions for some time before purchasing an 8.5X42. My wife and I compared the SLC 8x42 to the 8.5X42 SV on two occasions. There was simply no question in either of our minds that the "SV view" was a dead ringer for the old reliable "SE view" we knew and loved.

From my seat, you are 100% correct. Own an SE and everything else pales in comparison...until you look through a flat-field bin with great edges. Some may not care about refocusing, repositioning, etc. but I do. I want a relaxed, effortless view, something I've only found in a few models. I loved the 7X42 EDG (what a walk-in view that is) but the diopter and design issues raised too many concerns. Swarovski won the day with the Swarovision. FWIW, the only Swaro model prior to the SV of any interest to me was the 7X42 SLC. Swarovision is simply on another plane altogether.

Again, my wife and I agree with your sentiment. The SE really sets a visual standard few can attain and it becomes addictive...and expensive!
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Old Thursday 25th September 2014, 18:34   #12
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I can't hold my eyes at an angle for too long without massive eye strain (a lot of sinus issues and strong astigmatism affect this, I think) and so I don't value edge sharpness very highly at all; so long as they aren't so highly distorted that it looks as if my edges are completely smudged, I don't much care.

Justin
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Old Thursday 25th September 2014, 19:42   #13
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It's sweet spot size that matters (i.e. narrow field that is sharp edge to edge, or wide field that is sharp over a large portion of the view). I feel like a sniper looking through a scope when I use a bin that doesn't have a big sweet spot because my eyes like to wander/dart off-axis. I like to keep the area most likely to hold birds in the view (i.e. certain part of the landscape, portion of lake or marsh, face of tree or brush line), then look around that view for birds as I pan sideways. My first real bins were the Nikon 8x40 Classic Eagle, which have a very flat and astigmatism free view (7 degree). I was shocked when I first tried the Leica and Zeiss alphas and found, for all their other optical merits, that they did not allow for such easy off-axis viewing. I eventually switched to the Zeiss 7x42 Classic for its much brighter, higher contrast, phase-corrected view. Its wider field than my Nikon was nice, but I still felt constrained by the smaller sweet spot which resulted from having much more field curvature. I've very happy that Swarovski and Zeiss are now offering bins with the flat-field performance that I've take for granted from all of Nikon's best bins over the last several decades.

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Old Thursday 25th September 2014, 19:48   #14
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As one who uses binoculars primarily for hunting I value both highly.

Sad to say I've hit the ignore button for someone for the first time since joining this forum ; three posts in one thread on the same old story. It's so boring !
When you can tick off a Brit, you have REALLY screwed up! So, I will apologize to all, not approach this thread, again, and try to curb my participation in other threads. Thinking BF was equally about camaraderie, I was just speaking to my friend Perterra. Sorry for thinking. I'm not good at it.

Since Samandag won't see this post, I hope one of his friends will pass along my apology.

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Old Thursday 25th September 2014, 21:21   #15
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As one who uses binoculars primarily for hunting I value both highly.

Sad to say I've hit the ignore button for someone for the first time since joining this forum ; three posts in one thread on the same old story. It's so boring !
Samandag,

Let me point out something that should be obvious. Using the ignore button doesn't require that you announce that you're using it.

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Old Thursday 25th September 2014, 21:31   #16
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Moreover, if you were to try to understand what's being said it might be less boring.
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Old Thursday 25th September 2014, 22:28   #17
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There you go with that logic stuff, again.

Wish me luck. I'm getting ready to go out and spend $150 to get a new headlamp put in. I took my Equinox to two auto shops, yesterday, and one couldn't do it and the other wanted me to wait 24 hours!

'Remember when changing a headlamp took loosening 3 screws and then tightening them again!?

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Good luck on the headlight, it's an ordeal now to do anything other than change a bulb.
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Old Thursday 25th September 2014, 22:31   #18
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It's not the first time this issue is raised here, and what I've learn from the many discussions is: those that have binoculars with edges not so sharp, think sharp edges are not important; and those that have binoculars with sharp edges think it is important.
I dont know, my Conquest HD is pretty sharp, the Zen Prime HD is also pretty impressive, but I could be perfectly happy with my Leupold yosemite.

It's just not that important to me.
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Old Thursday 25th September 2014, 22:34   #19
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Keep on topic, please.
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Old Friday 26th September 2014, 00:21   #20
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Is it that simple?

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I dont think edge to edge sharpness is as important as wide field of view. I always center on my target. It might be more important in a telescope but for something as easy to move as a binocular it's not an issue for me. It's nice to see edge to edge sharpness, but not a must have for me.
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.

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... those that have binoculars with edges not so sharp, think sharp edges are not important; and those that have binoculars with sharp edges think it is important.
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.
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Old Friday 26th September 2014, 01:05   #21
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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.
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Old Friday 26th September 2014, 01:14   #22
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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.
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.
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Old Friday 26th September 2014, 01:16   #23
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Human vision is sharp to the edge, so maybe a good binocular should be also.
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Old Friday 26th September 2014, 01:30   #24
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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.

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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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Old Friday 26th September 2014, 01:56   #25
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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!

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