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Edge sharpness in Binoculars (1 Viewer)

I have a Vortex Viper 8x42 and a Nikon Monarch M7 8x30 that both provide a sharp image for about 50-60% of the radius(meassured from the center to the edge of the image as viewed in the binocular). After this the sharpness declines and the image becomes softer. Some of this softness can be adjusted for with the focus wheel, but not all.

The Viper HD has a slightly smaller sharp area in comparison to the Nikon Monarch M7. I started to think about this when i testet a friends Hawke Frontier ED 8x42, and that had a noticeably bigger sharp area than both of mine. I was a bit surprised since they are both similar priced.

How big area should be sharp on a pair of binoculars?




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Unless a bino has so-called "field flatteners" it will always have some degree of "field curvature". Not necessarily bad since not everything is always in the same distance from you. And our eyes mostly don't see the blurry edges unless we actively roll around our eyes in the field of view which is not really the normal use case for a bino for daytime use. It's more of a concern for a bino on a tripod where it's not as easily moved to follow an object. As when used for astronomy for example.
There are a number of binos with field flatteners in basically all price brackets.
One of the most affordable that I own was a used Canon 8x32WP (built like a tank).
But there are many others. From cheap Chinoculars to the Swaro NL Pure.
 
Like Jinac says, it depends on the price of the binoculars. Sharp edges usually cost more! Sharp edges cost more because the ocular has to be more complex to produce a flat image sharp to the edge, and usually requires a separate field flattener lens in the optical train. The Canon 10x42 IS-L has very sharp edges, but the Swarovski EL's followed by the NL's have probably the sharpest edges of any binoculars. Very sharp edges though can create problems like RB when you pan, and some people do not like the overly flat pie plate appearance of the FOV that field flatteners which are necessary for the sharp edges produce. Also, it seems that sharp edges with a big FOV as in the EL and NL go hand in hand with glare. That is why Swarovski's are often referred to as 'glare monsters'. A little more field curvature with corresponding softer edges gives you a more 3D or immersive feel, and that is why some birders like Leica's. You have to decide how you like your edges sharp or soft and if are you willing to pay for sharp edges.
 
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I only use bins handheld. Edge sharpness has never been an issue for me. Very low on IQ priorities.
For me, it depends on how fast or slow the fall off in sharpness at the edges are. If the fall off is fast, you notice it more than if it is slower and more gradual. Anymore I don't care if the edges are tack sharp like in the EL or NL, but I do like fairly sharp edges like in the Nikon HG versus the soft edges of a Leica. I would rather have a bigger FOV with fairly sharp edges than a smaller FOV with tack sharp edges because I find I can see more birds at the edge of a big FOV with fairly sharp edges and then move the bird to the center of the FOV. I miss fewer birds because of the bigger FOV. That is why I like the Nikon HG 8x42 with it's 8.3 degree FOV and fairly sharp edges better than the Swarovski EL 8.5x42 with its puny 7.6 degree FOV and tack sharp edges.
 
@OP - as you've seen, there are real differences between binoculars in the area that is sharp (often called the "sweet spot"; binoculars where the image is sharper/better corrected further from the center are said to have better "edge performance"). Older binoculars like Zeiss Jena 10x50s and 8x30s, whose optical designs date back to the 1930s, had wide fields of view, but their sharpness to the edge was not so good. More modern optical designs have improved the size of the sweet spot, and the trend for the last 10 years or so has been to incorporate what is called a "field flattener" which with many binoculars has the effect of increasing the sharp area much closer to the edge. In the past this technology was quite expensive, but now features in more affordable binoculars (eg the Hawke you tried).

Manufacturers/designers have different ideas as to just how much edge sharpness and flatness of field makes for the most pleasing image: some feel that some field curvature and/or edge blur makes for a more "natural" feel to the image. So the answer to your question "How big area should be sharp on a pair of binoculars?" is probably "what the manufacturer thinks it should be", or "however big you prefer it to be".

In terms of utility in the field, I feel it's a definite advantage to have a large sweet spot: it improves your all-round awareness, and when a target of interest is found, it's not as important to move it into the center in order to see it at its very best. If your eye accommodation is still good, it may be able to compensate for edge performance that is not so good; but your eye is still working harder, and over long sessions this can contribute to fatigue. But opinions as to the value of sharpness to the edge (as in the post above mine) certainly differ.
 
Hi,

well, it's complicated... first of all one needs to differentiate between field curvature (which can be focused out or be corrected by a field flattener aka Smyth lens) and off-axis aberrations which cannot be corrected - a common case is a certain degree of off-axis astigmatism which is accepted as tradeoff for desired features in an optical design.

As for field flatteners - not all of them are created equal, some have a nice and wide sweet spot and get a tiny bit fuzzy at the very edge, some are tack sharp in the center and at the very edge with a slightly less sharp ring in between, not so affectionately called Absam ring - after the town in Austria that the instruments with this feature originate from...

Also it's a matter of taste, some people love flat field bins, some hate them. I personally am fine with a wide true field with some fuzzyness at the edge for hand-held binoculars - you will still notice a movement at the edge and can quickly center the bins on the moving bird.
For mounted instruments wide flat fields are preferred, especially in cases without automatic tracking (as in dobsonian astroscopes).

Joachim
 
Hi Naturebird, how big should the sweet spot be? Up to you. How often are you looking near or at the edge of the field (often that's actually difficult to do) and how clearly do you need to be able to see detail there? In terms of finding moving birds/wildlife, I find a reasonably large FOV in the first place more important than edge sharpness, but wouldn't want the outer field too soft, and certainly not smeary as with bad coma or astigmatism, so it does get complicated. Most bins (even fine ones) aren't fully sharp to the edge, yet are still usably sharp for practical purposes. Also, many bins just limit their FOV so that more of it looks sharp, but then they don't have the rest at all, so do also take FOV into account when comparing performance.

Sometimes one bin is just better than another, even at a similar price, but many trade-offs are involved in design and cost of materials. If that Hawke has a (relatively?) larger sweet spot, is there anything else your two do better?
 
...it depends on the price of the binoculars. Sharp edges usually cost more! Sharp edges cost more because the ocular has to be more complex to produce a flat image sharp to the edge, and usually requires a separate field flattener lens in the optical train. The Canon 10x42 IS-L has very sharp edges, but the Swarovski EL's followed by the NL's have probably the sharpest edges of any binoculars. Very sharp edges though can create problems like RB when you pan, and some people do not like the overly flat pie plate appearance of the FOV that field flatteners which are necessary for the sharp edges produce. Also, it seems that sharp edges with a big FOV as in the EL and NL go hand in hand with glare. That is why Swarovski's are often referred to as 'glare monsters'. A little more field curvature with corresponding softer edges gives you a more 3D or immersive feel, and that is why some birders like Leica's. You have to decide how you like your edges sharp or soft and if are you willing to pay for sharp edges.
🙄
The above from denco is mostly rubbish in my opinion and ought to be ignored.

The bit e.g. about "sharp edges...EL & NL...Swarovski...glare monsters"

Sep 18, 2023
I tried all the NL's and I had problems with glare in all of them unless I got the eye cups adjusted exactly right,
So when you adjusted all the different Swarovski NL binoculars exactly right you weren't troubled by glare.
Excellent, good to know, please remember this.

And yet it is you denco, who subsequently termed the phrase "glare monsters" and now often use it to denigrate the NL; as shown by a simple forum search for the phrase combined with you as author.
 
How big area should be sharp on a pair of binoculars?
If you are in a buying process and have found a pair of binoculars that you like for one reason or another, there's one thing to consider if you're not sure about whether the sweet spot is big enough: The closer your subject is to you, the larger the sweet spot should be. Picture a distant bird in your diagram and it will be inside the 50%-ring and perfectly sharp. Watch birds at your feeder in the garden through a 10x and you will wish for a 80 or 90% sweet spot.
 
Hi,

….. first of all one needs to differentiate between field curvature (which can be focused out or be corrected by a field flattener aka Smyth lens) and off-axis aberrations which cannot be corrected - a common case is a certain degree of off-axis astigmatism which is accepted as tradeoff for desired features in an optical design.
Joachim
I think this is a very important point, which needs to be reiterated.
 
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🙄
The above from denco is mostly rubbish in my opinion and ought to be ignored.

The bit e.g. about "sharp edges...EL & NL...Swarovski...glare monsters"

Sep 18, 2023

So when you adjusted all the different Swarovski NL binoculars exactly right you weren't troubled by glare.
Excellent, good to know, please remember this.

And yet it is you denco, who subsequently termed the phrase "glare monsters" and now often use it to denigrate the NL; as shown by a simple forum search for the phrase combined with you as author.
If I have to stand on my head and jump through hoops to try to eliminate glare I really don't care to own that binocular and that is the way it was with a lot of the NL's I tried, especially the NL 8x42 and NL 8x32 and even standing on my head I still had glare in certain situations. With the Nikon HG 8x42, I can place my eyes anyway I want and stand on my feet and I don't get any glare. That is the main reason I sold my NL 8x32. I liked the sharp edges and slightly bigger FOV of the NL, but I couldn't tolerate the glare in the bottom of the FOV. The NL is superb EXCEPT for the glare. You never knew when it would show its ugly head. Here are some threads talking about glare in Swarovski NL's and Swarovski's in general.

Holger Merlitz
"Who already owns the EL WB would hardly gain from an upgrade to the NL Pure, since both are virtually playing in the same league. The stray light issue which has occasionally been reported to plague the EL WB has not been resolved with its successor, and this is going to remain a matter of dispute whenever the NL Pure's merits are discussed."

Holger Merlitz
"I have been testing the 8x32 NL for 2 weeks and have used it many times. There is indeed a stray light problem, and it behaves very similarly to what you described, albeit depending on the situation. Foremost, I would like to say that the 8x32 NL Pure is (in my opinion) the best 8x32 I have seen so far. The large field of view, bright, edge-sharp image, very little color fringing, the superb feel - almost everything is perfect. As you have already observed, the panning behavior is also exemplary: no globe effect, the image rolls gently past the eye - it couldn't be better. I actually always see stray light when the eyecups are fully extended, but that is not the optimal position for me anyway. If I turn them in one notch, the stray light is already reduced. I turn the eyecups in another notch, and in many situations the stray light is completely gone. Unfortunately, my eyes are then so close to the eyepiece that I occasionally get shadows. So I'm currently learning how to use the binoculars with the eyecups in this position and at the same time avoid the shadows. The stray light problem is thus shifted into a viewing problem that can probably be managed with a bit of practice. Nevertheless, it does happen that when you pan, your eyes briefly deviate from the ideal viewing position and then the stray light briefly appears again. The cause is the brightening near the exit pupil, which I have framed in your photo. The positions of these brightening vary depending on the incidence of light, they are usually in the lower area when the sky above the field of view is bright. A few days ago, I often had to struggle with these brightening in dull, cloudy weather. My 8x30 Nikon E2 with a similarly large field of view had no problems here. Yesterday, under blue skies and bright sunshine, there were no stray light problems with the NL Pure, and I was able to enjoy these otherwise great binoculars without any restrictions. On cloudy days, the pupils of the eyes are dilated and come into contact with these bright spots, in which the white clouds are reflected much more often. Under blue skies, the problem is then blown away. So it's a difficult case. I like these binoculars and am therefore doing my best to deal with this stray light, because you are rewarded with this superb image. But this elephant called stray light is always in the room, and occasionally it runs through the field of view, trumpeting loudly...

Owlbarred
"I've had horrible problems at dusk with veiling glare on my dearly loved 8x32 EL FP's while doing daily sunset/twilight counts of northern harriers coming to a distant tall grass prairie roost. Unfortunately, because of landowner issues, access is limited, and the roost is viewable only when facing westward, though not directly into the setting sun. Frankly, until the roost counts, I never realized I had such a terrible VG problem."

FrSt
"However, my 8x32 NL Pure model is, in my opinion, extremely susceptible to veiling glare; you don't have to look into the sun for that to happen. You could almost say that there are few situations where no stray light effects are visible. Outdoors in sunshine or on cloudy days. So, my question to the experts: Can it really be that such expensive binoculars are so susceptible to stray light? Or is it more likely that I received a decentered model? Is that even possible with regard to stray light? Apart from that, the image is absolutely brilliant. When I look at the eyepiece (closed lens cap, from a distance of 40cm) I see two reflections (false images?) of myself. Is this normal due to the concave first lens element? When I open the lens cap and hold the binoculars up to the sky, in addition to the reflections of myself, I see (several!) light reflections in the lens system as well as diffuse stray light which shows the optics inside. I tried to take a picture of it with my cell phone and attached it here. When I compare it with the pictures on Allbinos, I get the impression that it is no better at all than the simplest binoculars tested there."

 
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People provoke so much of this by continuing to ask "but didn't you previously..." etc. The problem has been amply documented, so resist the temptation.
 
there's one thing to consider if you're not sure about whether the sweet spot is big enough: The closer your subject is to you, the larger the sweet spot should be. Picture a distant bird in your diagram and it will be inside the 50%-ring and perfectly sharp. Watch birds at your feeder in the garden through a 10x and you will wish for a 80 or 90% sweet spot.
Interesting observation. This is purely subjective (but would like to know if others see the same) - I have found that when birds are at closer range, the sweet spot I perceive with most binoculars also seems larger. Maybe my eyes have better accommodation at shorter range, or maybe the larger images give more visual cues, but everything is easier the closer targets are. That's part of the reason why I consider detail at distance to be the stiffest test (unfortunately, one that is also needed in a lot of my birding).
 

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