Wide flat field and edge sharpness an illusion? (1 Viewer)

[Tringa45]

This is a great thread!

So my question is, which makes/models of binocular have good edge sharpness, decent eye relief for eyeglasses, and minimal flare/glare and blackouts?! The EL?

For many years, I didn't care much about edge sharpness, but I value it now. There are times where I dart my eyes, like Alexis mentioned. Or times where I don't have my eyes centered well for a quick look.

There are also times that I use binoculars on a tripod. I like to let my eyes wander around the field.

I live in an urban/suburban area but we have many greenspaces mixed in. During my walks, I can observe several wetlands with small creeks from the sidewalk, along busy roads.

Typically, I rest my elbows on the fencing along the sidewalk and look upstream or downstream in these wetlands. So I look side to side, plus near and quite far, but I keep the binocular stationary. I don't scan by moving the binocular, as I focus more on detecting movement which requires the view to be stationary. I just move my eyes around.

When I had a Kowa 8x33, I would get blackouts if I darted my eyes. I had an 8x42 SLC for a few years, which I really enjoyed, but the edges were not sharp/flat and I started noticing bad flare/glare unless I positioned it correctly.

Maybe I need to reconsider the EL. I was never impressed with them but maybe I need some more time with one.

I think you will be compelled to pick two.
ELs have excellent edge correction and comfotable eye relief and this probably applies to the NLs as well, although I have not had one on a tripod.
My EL, however, is not particularly good at suppressing glare and the consensus is that that applies to both model ranges.
I too have a Kowa Genesis 8x33. Eye relief and edge sharpness are not its forte and comfort is also impaired by vignetting.

Btw, I see that there are still some doubters on this thread and would suggest that they look in a mirror and incline their heads to one side by about 30° (about half an AFoV). They would then observe the extent of lateral pupil movement, which has to be compensated by head movement in the opposite direction, as you have done with a fixed binocular.

John

 

[4th_point]

I think you will be compelled to pick two.
ELs have excellent edge correction and comfotable eye relief and this probably applies to the NLs as well, although I have not had one on a tripod.
My EL, however, is not particularly good at suppressing glare and the consensus is that that applies to both model ranges.
I too have a Kowa Genesis 8x33. Eye relief and edge sharpness are not its forte and comfort is also impaired by vignetting.

Btw, I see that there are still some doubters on this thread and would suggest that they look in a mirror and incline their heads to one side by about 30° (about half an AFoV). They would then observe the extent of lateral pupil movement, which has to be compensated by head movement in the opposite direction, as you have done with a fixed binocular.

John

Thank you, sir.

You are correct about the head movement. When mounted on a tripod, I move my head and eyeballs around to see the full view.

I tried the 8.5x EL, 8x30 CL, 8x30 SFL, and several compacts at the local Audubon the other day. They all had noticeable amounts of glare/flare when looking up into the fir trees. My 8x42 SLC had very noticeable flare/glare as well, but I was overall happy with it for ~2 years. I'd just like something better for that, if possible, and am willing to give up some other characteristics. A step down in size and weight would be preferred as well but that might be a competing objective!

FWIW, my 15x50 Canon has minimal flare, even when really trying to induce it.

Jason

 

[Swedpat]

These attributes combined with adequate eye relief for glasses wearers are an outstanding (and recent) optical achievement, but for hand-held binoculars they are of no practical value.
The fovea of the human eye, where highest visual acuity for 20/20 vision is achieved only has a visual field of 1° and outside this, visual acuity degrades more rapidly than the off-axis resolution of a binocular.
If we wanted to view the field edge of a typical binocular with 60° AFoV we would have to redirect our eyes by about 29°. However, the eye's pupil is at about 11 mm radius from the centre of the eyeball, so a 29° redirection is accompanied by rotation and about 5 mm lateral movement, sufficient to result in a complete blackout in most binoculars!
Of course we just don't do this and simply redirect the binocular to place an object of interest in the field centre.
Should there be any doubts about this, I suggest placing a binocular on a tripod and viewing a detailed plane surface (or bookshelf). To see detail in the left field it is necessary to move one's head to the right and vice versa. This technique is often used by amateur astronomers, whose telescopes are always tripod mounted and where eyepieces with up to 110° AFoV are sometimes used.
It is often asserted that for daylight viewing one does not need more than 2,5-3 mm exit pupils but they result in a loss of viewing comfort.
The complaints of veiling glare in some modern designs can perhaps be attributed to their complexity and the "poor" edge performance of Ultravids, SLCs and FLs, particularly those of lower magnification and large exit pupils is in practice more advantage than detriment.

John

I don't agree that sharpness across the entire FOV is not of practical value at free hand use. Yes, it's not as important at free hand use as when it's mounted because we often automatically move the binocular in order to place the observed object in the center.
I have a 5x25 ultrawide with 14-15 deg TFOV.
Only half of the field width is sharp. And while the unsharp area is still useful because it helps to discover an object in order to place it in the sharp center, sharpness across the entire FOV definitely would be better. I just dream about a Swarovski NL Pure 5x25!

 

[james holdsworth]

Coming from decades of non flat field binoculars to an owner of said, my opinion would be that to achieve the flat field is not worth the trades offs - rolling ball, AMD at the edge and areas of unsharpness outside the central sweetspot.

In terms of overall image quality, I still much prefer my HT over my SF. Unsharp edges yes, but, IMO, everything else superior apart from FOV….better contrast, colour fidelity, glare control and a brighter, more saturated (more pleasing) image, as well as a more relaxed image, both in terms of panning behaviour and just ease of view.

 

[Swedpat]

Coming from decades of non flat field binoculars to an owner of said, my opinion would be that to achieve the flat field is not worth the trades offs - rolling ball, AMD at the edge and areas of unsharpness outside the central sweetspot.

In terms of overall image quality, I still much prefer my HT over my SF. Unsharp edges yes, but, IMO, everything else superior apart from FOV….better contrast, colour fidelity, glare control and a brighter, more saturated (more pleasing) image, as well as a more relaxed image, both in terms of panning behaviour and just ease of view.

There is a confusion about the terms used here.
I have discussed it earlier at Cloudy nights forum.
In my understanding a flat field means undistorted. Therefore I have reacted when it is commonly said that a flat field results in rolling ball effect. I mean that rolling ball effect is a result of barrel distorsion. At least it is my experience. A sharp undistortioned image does not result in rolling ball effect.
Flat field is defined as sharpness across the entire field of view. This is simply a wrong definition. Flat is not the same as sharp.
Flat = football field.
Curved = a velodrome.
Both can be sharp to the edges.

Whether the image is sharp to the edges has nothing to do with if it is flat or not. Both example exists.
Despite english is not my mother language I understand something went wrong the definitions of the terms used in this topic.

 

[Maljunulo]

I suppose I liked the flat field of my EL SV 10X42, but I detested the rolling ball, and had to force myself to ignore it, but it really bugged me.

My SF 8X32 is much better.

I find that the lack of a flat field in my Habicht 8X30 W doesn’t bother me in the slightest.

I’m not sure what all that means, but that’s the way it is.

 

[james holdsworth]

There is a confusion about the terms used here.
I have discussed it earlier at Cloudy nights forum.
In my understanding a flat field means undistorted. Therefore I have reacted when it is commonly said that a flat field results in rolling ball effect. I mean that rolling ball effect is a result of barrel distorsion. At least it is my experience. A sharp undistortioned image does not result in rolling ball effect.
Flat field is defined as sharpness across the entire field of view. This is simply a wrong definition. Flat is not the same as sharp.
Flat = football field.
Curved = a velodrome.
Both can be sharp to the edges.

Whether the image is sharp to the edges has nothing to do with if it is flat or not. Both example exists.
Despite english is not my mother language I understand something went wrong the definitions of the terms used in this topic.

My use of the term flat field implies the use of a field flattener lens to achieve (roughly equal) sharpness across the entire field, along with the inherent side effects of that choice.

 

[Tringa45]

There is a confusion about the terms used here.

In my understanding a flat field means undistorted.

These are two characteristics independent of one another.
If one directs an objective lens perpendicularly at a flat surface (e.g. a wall with a structured surface) the image of that surface will be curved towards the lens.
When viewing that image through an eyepiece it would only be possible to get a sharp image of the field edge (if both objective and eyepiece were relatively free of astigmatism) by refocussing.
Field curvature can be corrected by a field flattener lens in front of the eyepiece.

There are two types of distortion and they are mutually incompatible.
Rectilinear distortion is the curvature of straight lines (either pincussion or barrel).
Zero rectilinear distortion (straight lines being depicted as straight) would result in angular magnification distortion and round objects at the field edge would be depicted as elliptical.
Conversely, zero angular magnification distortion would result in pincussion distortion.

John

 

[tenex]

Many threads have struggled with terminology here because the famous Swarovision did these two things at once: flattening field curvature, and fiddling the distortion profile to reduce pincushioning, at the cost of causing some RB. As do SFs and NLs (arguably better), while several other models like MHG are only attempting the first. So what do we call the combination then? Not "flat field" because that's only half the story, not "Swarovision" because Zeiss has now done it too (and even Sky Rover now!)... a new term is needed.

 

[Swedpat]

By the way: is the problem with the confusion in this topic that the english language is unlogical? There are a number of example of this.
I have earlier written about that the common expression "a pair of binoculars" is actually not correct. The word binocular means 2 oculars.
So technically a pair of binoculars means 4 oculars. But still it is used about 2 oculars.
But now and then it is actually said "a binocular".
The swedish word for binocular is "kikare". It is directly translated as "peeper". So for me a binocular is 1 instrument. Technically binocular is 1 instrument consisting of 2 parallell connected small low powered telescopes.
But in Sweden "kikare" can be used even for other optical instruments as well.
Actually swedish language has taken some of expressions from english. We say "ett par jeans"(a pair of jeans) and "ett par kalsonger" (a pair of underpants). It is a single garment, but is called a pair.
I just wanted to demonstrate that the language is sometimes unlogical and this can result in confusion.

 

[tenex]

By the way: is the problem with the confusion in this topic that the english language is unlogical?

No.

 

[Maljunulo]

All natural languages are more or less illogical.

Constructed languages much less so.

 

[Scott98]

Many threads have struggled with terminology here because the famous Swarovision did these two things at once: flattening field curvature, and fiddling the distortion profile to reduce pincushioning, at the cost of causing some RB. As do SFs and NLs (arguably better), while several other models like MHG are only attempting the first. So what do we call the combination then? Not "flat field" because that's only half the story, not "Swarovision" because Zeiss has now done it too (and even Sky Rover now!)... a new term is needed.

Was it Nikon that actually did this first with their HG/Premier/LXL binoculars? Not sure when they first came out. Every designer chooses their own balance of distortion effects and AMD. My favorite blend is in the 7x42 EDG and Swaro 10x56 SLC. They both seem nearly sharp to the edge with very little bending/warping of the field as you pan around.

Conversely, my 8x42 SF's feel like viewing the world from the inside of a fishbowl. But I think that's inevitable as the AFOV stretches beyond 63ish degrees. I enjoy all of them but somehow I find the SF's don't bother me when doing astronomy. Tolerance for these effects varies widely I think...some people don't notice any of this stuff.

 

[Elkhornsun]

I know from my own experiences that a color cast as with the Zeiss or flare in marine use or lack of contrast will be a problem. MTF numbers are less relevant to my enjoyment using binoculars. The outer edges are not important when I am using binoculars.

I understand that manufacturers are selling basically the same product and need to find way to differentiate their products in the minds of the consumer. Binoculars for the most part do not wear out and so the bino companies need to offer a compelling reason (real or perceived) for existing customers to buy new ones.

 

[tenex]

Was it Nikon that actually did this first with their HG/Premier/LXL binoculars? Not sure when they first came out. Every designer chooses their own balance of distortion effects and AMD. My favorite blend is in the 7x42 EDG and Swaro 10x56 SLC. They both seem nearly sharp to the edge with very little bending/warping of the field as you pan around.

I don't know, I've never seen those Nikons. Did they have a complex distortion profile like Swarovision? I agree about the SLC, it has just the right amount of pincushioning not to bend straight lines too much, yet still pan naturally. Most bins have more than that, Leicas most of all, whose rationale I've always wondered about. (The exception was the recent Trinovid BR 42, which they buried quickly.)

 

[dorubird]

The most balanced binoculars in the management of geometric deformations are Zeiss SF 8x42 and 10x42. It has geometric distortions present in that way so that the globe effect does not appear like in Swarovski EL and NL Pure but, in the same time, it does not have big distortions like in Leica Ultravid. This Zeiss SF is fixed in the middle, having best from two worlds!
SF clever geometric distorsion management also counteract the lower magnification on the edges, that cause EOFB. Binoculars like Swarovski EL or NLPure for example, pays tribute to the lack of geometric distortions with compresses of objects on the edges. So due to this smaller magnification on the edge of FOV, the edge of the field appear brightened a little than the center of FOV, when looking at night sky with EL or NLPure. This is well known EOFB in astronomy (Edge Of Field Brightness).
In conclusion in 42SF range we have zero EOFB and no Rolling Globe due to very clever placing of small geometric distorsion

 

[hopster]

In terms of overall image quality, I still much prefer my HT over my SF. Unsharp edges yes, but, IMO, everything else superior apart from FOV….better contrast, colour fidelity, glare control and a brighter, more saturated (more pleasing) image, as well as a more relaxed image, both in terms of panning behaviour and just ease of view.

I also greatly prefer the HT to the SF, at least in 8x which is the only serious comparison that I have made.

 

[Alexis Powell]

Was it Nikon that actually did this first with their HG/Premier/LXL binoculars?

Nikon made such bins (with flat field and with high correction for off-axis astigmatism) for many decades prior to the HG/LX. Their astro-oriented porros (recently discontinued) are their oldest that I know of. Their first flat-field and well-corrected roof was the 8x40 Classic Eagle. For me, the HG/LX/LXL were notable for having really strong rolling-ball effect, esp. the 10x42 model, which is different from their other flat field models. Many long threads on these topics are available in the BirdForum archive.

--AP

 

[Maljunulo]

I thought the rolling ball was much worse in my 10X42 EL SV than the 10X42 Venturer LX, which it replaced.

It required a constant effort to overlook RB in the Swarovski glass.

 

[Alexis Powell]

I thought the rolling ball was much worse in my 10X42 EL SV than the 10X42 Venturer LX, which it replaced.

It required a constant effort to overlook RB in the Swarovski glass.

Interesting that your experience is the exact opposite of mine. In general, I don't get rolling ball from Nikon bins w/flat field, but the 10x42 LX is so strong, I almost feel the need to duck to avoid being hit by objects that come flying toward me as they move from edge to center of the view during panning! The effect in the Swarovski looks to me much more modest and the rolling is restricted abstractly to the view in the distance.

--AP