Binocular Evolution I: Field of View (1 Viewer)

[tenex]

The development of modern binoculars seems actually to have gone backwards from wider fields of view to narrower ones, inspiring some to prize older models for their FOV while others remain content with less, or even claim to like a more limited view for eliminating distraction or "framing" an isolated "vignette" of a scene (as in a review recently quoted here) -- which sounds absolutely perverse to me, perhaps even a whiff of sour grapes. Cameras can isolate an element this way to artistic effect in a photograph, but a binocular is live view, with eyes that have a limited zone of central sharpness anyway accompanied by wide peripheral vision. Why suffer tunnel vision that restricts it any more than necessary?

Roof-prism binoculars (Dialyt, Trinovid) were aggressively marketed by Zeiss and Leica in postwar West Germany as a more elegant alternative to traditional Porro models produced at lower cost by CZ Jena and Japanese rivals, despite having inferior optical performance due both to phase interference (poorly understood at the time) and generally narrower fields of view, which anyone would detect immediately. Why narrower? One can imagine two possible reasons.

* Bulk. Smaller, lighter instruments (however appealing) require smaller prisms, which tend to limit FOV especially at lower magnifications, even with increasingly sophisticated eyepieces. This seems quite straightforward. The handful of recent models that finally offer significantly wider FOV again are also noticeably heavier and/or larger... perhaps tolerable now because Porro models (and the crucial marketing contrast with them) have been forgotten?

* Sharpness. Wide-field instruments tend to have a larger outer area that isn't quite sharp, due to field curvature and other aberrations. Restricting FOV can be seen to offer the "benefit" of greater overall sharpness in the remaining field. Once again this strikes me as thoroughly perverse reasoning... and yet, the recent wide-field models do also all have a flat-field design with sharp edges (WX, NL, and arguably SF).

If not for this second consideration, wouldn't we also have had conventional models with wider FOV by now? If the FOV of an EII 8x30 could be packaged in a roof-prism body, with FL glass and perhaps a slightly larger sweet spot, I'd expect that to sell like hotcakes... so why (for example) wasn't Swaro EL originally designed this way, to help birders once again get on birds better? And how did this manage never to happen at all, despite being technically straightforward?

I have a personal interest in these questions: I just described a bin I'd like to carry myself, and my wife would be more eager still to have. In 2010 (an amazing year for Swarovski) buyers could choose between brand-new EL SV and SLC HD, each a major upgrade on previous models, one the new flat-field wonder, the other a triumph of conventional design. We wish this was happening again now: that NL had replaced EL as the new flat- field model, while SLC also got a wider field, offering a similar choice today. We want something like an SLC+ with ~70° AFOV (and no FieldPro). Why does it seem that this will never be made, even by Leica whose Noctivid didn't join the mad rush to a flat field?

[I've described the Swarovision approach merely as "flat-field" but of course it's more than that; see Part II, Curvature and Distortion, here]

 

[wdc]

Do you care whether it is a porro or a roof? The FOV needs to be around 9°?
Maybe APM can do it. They have the 6 x 30, 9.3° porro model, made in China, which several forum members own.

APM-MS-6x30 Binoculars

The APM-MS-6x30 binoculars in classic design with BAK4 Poro prisms impress with their excellent price/performance ratio. @30mm clear aperture@6x [email protected]° field of view@diopter compensation ±5@high light gathering capability@full FMC multicoating@Weatherproof and waterproof

www.apm-telescopes.net

-Bill

 

[Binocollector]

The Kowa BDII 8x32 has the same FoV as the Nikon EII. And less field curvature than the 6.5x32. I tested it in a store once and was impressed. I still bought the 6.5x32 in the end as I wanted the smaller magnification/larger exit pupil. But the 8x32 is sweet.
I wish something like the Leitz Amplivid was still made.

Legendary binoculars - Leitz Amplivid 6x24 - Leitz Amplivid 6x24 - 1956-1962

It’s difficult to say when exactly the first pair of binoculars was created. An idea to put two telescopes together was perhaps not exactly difficult to come with; it most probably occurred not later than at the beginning of 17th century, with the usage of the first refractors ...

www.allbinos.com

 

[kimmik]

To design a wider FOV bino one can do the following:

1. faster objective, then correct the aberrations with all your alpha skill
2. bigger prism and eyepiece, until it no longer fits in your desired body shape
3. longer body to move the prism as far back as possible, for a larger image circle, until you prefer a shorter body

SF - give up 1, focus on 2 and 3, market it as ergobalance
NL - 1 2 and 3, but heavier
NV - give up 3

The one commonality shared by all three premiums, is big prism. SF puts it furthest back, NV puts it as far forward as possible to shorten the bino at expense of FOV. Finally NL is somewhere in between.

 

[kimmik]

We wish this was happening again now: that NL had replaced EL as the new flat- field model, while SLC also got a wider field, offering a similar choice today. We want something like an SLC+ with ~70° AFOV (and no FieldPro). Why does it seem that this will never be made, even by Leica whose Noctivid didn't join the mad rush to a flat field?

Optically NL replaced both SLC and EL, with AMD distortion somewhere in between, while maintaining flat field. The NL physical design is completely new and is neither EL nor SLC.

A new 70° AFOV SLC would be better renamed SLW:
Option 1. The feature of "small light compact" will suffer to achieve the wider AFOV, just look at the NL eyepiece. The SF 32 has smaller eyepieces but achieved this by being longer and not small not compact.
Option 2. Alternately the eye relief can be reduced to keep eyepiece size, weight and SAEP reasonable, perhaps from 18mm to 14mm. This would be the SLW, small light wide. Glasses wearers back to the NL (or noctivid or helia s at 60°).

The only way out of this dilemma is new glass or new surface types. The NL kind of cheated, its achievement is mainly in the packaging, allowing greater total glass. Even then it dropped the eye relief a little to give designers some breathing space.

Maybe in the longer distance future.

 

[William Lewis]

I too bemoan the demise of the porro. I suppose the ease of waterproofing a roof compared to them is another reason alongside size and weight. I think there's definitely room in the market for someone so step out and make one, just look at the prices of Nikon se's now!

 

[Troubador]

If the FOV of an EII 8x30 could be packaged in a roof-prism body, with FL glass and perhaps a slightly larger sweet spot, I'd expect that to sell like hotcakes... so why (for example) wasn't Swaro EL originally designed this way, to help birders once again get on birds better? And how did this manage never to happen at all, despite being technically straightforward?

Didn't Nikon's E II 8x30 have 154m @ 1km? If so, Zeiss's SF 8x32 having 155m seems the answer to your prayer.
Or not?

Lee

 

[tenex]

Do you care whether it is a porro or a roof? The FOV needs to be around 9°?

Yes, it should be a roof (otherwise EII is fine), but no, 6-7x is insufficient magnification for most of our purposes.

Zeiss's SF 8x32 having 155m seems the answer to your prayer.

Maybe hers. I thought someone might suggest this, despite its having a (nearly?) flat-field design which isn't my preference. I've tried the 8x32 only briefly, and should take a more careful look at it, with my wife. I also dislike open-bridge design (and Zeiss isn't my general favorite) but apart from the newly raised price, she might like it better.

 

[Charlie Yardbird]

The development of modern binoculars seems actually to have gone backwards from wider fields of view to narrower ones, inspiring some to prize older models for their FOV while others remain content with less, or even claim to like a more limited view for eliminating distraction or "framing" an isolated "vignette" of a scene...

* Sharpness. Wide-field instruments tend to have a larger outer area that isn't quite sharp, due to field curvature and other aberrations. Restricting FOV can be seen to offer the "benefit" of greater overall sharpness in the remaining field. Once again this strikes me as thoroughly perverse reasoning... and yet, the recent wide-field models do also all have a flat-field design with sharp edges (WX, NL, and arguably SF).

So what is exactly is gained by a purpose-built narrower FOV, for the same money, compared to putting a donut on the objectives of your wide field to block out the edges you don't like (but maybe your wife DOES like)? Instead of buying two dissimilar bins, buy extra lens covers & use a hole saw to make a donut.

(Am I going to have to go into the Birders Protection Plan to hide from the Optics Marketing Mafia?)

 

[tenex]

No, just read again. I was summarizing the typical approach; my/our own preference is for wider FOV.

 

[Patudo]

I think "the market" has had the opportunity, on more than one occasion, to give a thumbs-up or thumbs-down to extra wide field binoculars, and the verdict of the market as a whole has been that extreme fields of view are not the be-all and end-all. Prior to WWII Zeiss produced an 8x40 with a FOV of over 11 degrees, and post-war there were the extra wide field Japanese 7x35s with FOVs from 10 to as much as 12 degrees, as well as the original prism-mirror Leitz Trinovids with remarkable FOV. There were some extra-wide 8x30s and the KOMZ 6x24, too. Had wide FOV been the ultimate desideratum in binoculars, manufacturers in Germany and Japan (not to mention the US, which produced examples such as the 6x42 Sard and 7x50 Mk 41) would no doubt have met that demand. But the preference seems quite clearly to have been for smaller (at least smaller than the widefield porros, which tended to be pretty bulky) and less expensive devices. There's no doubt that binocular manufacturers did respond to demand from the market: besides superior waterproofing, they must have realized the growing number of people wearing glasses needed to be taken into account, as longer eye relief binoculars began replacing models with shorter eye relief in manufacturers' lineups from as early as the 1970s. Combining long eye relief and a wide field of view is a challenging ask for optical designers; it can now be achieved at considerable expense (NL, WX) but until quite recently it has been necessary to choose one or the other, and the choice has very definitely been on the side of long eye relief. I guess the market has spoken.

In practice, although a wide FOV is indeed very pleasant, it's not absolutely necessary in many situations. Maybe I'm showing my age here, but I feel even the old standards of 110m for a 10x40 and 130m for an 8x30/32 are perfectly adequate for field use, especially if the image is well corrected to the edge. Modern fields of view are a luxury.

I think most binocular users would agree that good edge performance can greatly compensate for a smaller field of view. Manufacturers have worked hard to improve edge performance because of the limitations imposed on field of view by the necessity for long eye relief, and I guess this approach has continued even as technology has enabled wider field of view. I can't imagine Swarovski, which has pretty much defined the character of its image by outstanding edge sharpness, developing a binocular inferior in that respect to the EL/NL - it would seem like a retrograde step. But one doesn't need to go with Swarovision if you simply can't get along with it. The Monarch HG formats (8x30 or 8x42) have the same FOV as Nikon's great classic 8x30E porro.

 

[Binocollector]

I might have to ad some thoughts on the wide angles -- since my last post in this thread I acquired a Komz 6x24 and an 11.5°, 6x25 "miniature bino" as well as a wide angle 6x18 (Gijs suggested it might be from the 1940's).
I also have 11° and 10.5°, 7x35s and multiple 10°, 8x30s. As well as the Kowa BDII 6.5x32 (which has excellent eye-relief).
The older ones are all very different. None of them can really be used with glasses but the eye-relief of the Komz 6x24 for example is much better than that of the 7x35 Japanese porros (at least my eye-lashes don't touch the glass on the Komz). The 6x24 is also rather small. The one that surprised me the most however was the J-B93 "miniature bino" with 11.5°. Yes, it has less eye-relief than the Komz, but the image is the most balanced of the 6x-binos. Less "compression" at the edge (it is probably in fact higher pincushion distortion that makes the image seem more balanced and less "distorted" at the edge when it has in fact higher rectilinear distortion) than even the Kowa BDII (but less eye-relief of course) -- the Kowa 6.5x32 not only has lots of field curvature (some say too much) but also a strange kind of compression going on at the edge which to me seems to be caused by too little pincusion distortion.
And the miniature bino has the best build quality of probably all my older binos. I was very impressed and I love the "form follows function" approach.
A more rare class of wide angles but probably the best when it comes to edge-sharpness and eye-relief are vintage wide angle 7x50s from the 70's. They don't pop up as often as the 7x35s but in general are better. I managed to buy 3 of them on ebay during the last 2 years. The best is my "Scope" 7x50 with a stated 580ft/1,000yds (11°) -- it has the best sharpness at the edge, Bak4-prisms, almost usable with glasses if the eye-cups were not as deep, excellent center sharpness. They do have rubber eye-cups that easily fold down but the lens is still a few millimeters recessed which truncates the view. But they are very impressive.
The only ones BTW that do have that "wow"-effect for me are the 10°, 8x30s. Those are the ones where it seems like the edge of the FoV is disappearing when putting them to your eyes -- but on those, eye-relief is also horrible.
Other models like the Komz 6x24 don't even feel that wide when using them, probably because of the same low pincushion distortion that the Kowa BDII has. In fact the Komz 6x24 has almost no visible pincushion distortion for my eyes -- the image characteristics are very, very similar to the Kowa BDII 6.5x32. Low pincushion, tons of field curvature (the Komz has a bit less than the Kowa), less balanced than the super wide angle Japanese porros which I think have the right amount of pincushion distortion for a more balanced view.
I agree that it is not the "be all, end all" but "nice to have". Sometimes I do prefer more moderate FoV with better eye-relief -- mainly for astronomy where I like to leave my glasses on due to astigmatism. So a 6.1° FoV for a 10x56 with 20mm eye-relief is perfectly suited for that purpose.
And I do like my Canon 8x32WP with field flattener oculars and 7.5° FoV. I wish Canon would make non-IS binos again.
But -- some of the old wide angles are definitely more usable than others and there is a lot of variation.

 

[Wasabrot]

I have read the Komz 6x24 has only a small area where the image is sharp. @Binocollector: Can you confirm this?

 

[Binastro]

The Komz 6x24 has I think a good sharp area, but it is night now, so I'll have to try again in daylight.

It has from memory special eyepieces unique to the 6x24 and maybe the 4x16.

B.

 

[Binocollector]

I have read the Komz 6x24 has only a small area where the image is sharp. @Binocollector: Can you confirm this?

No. I think it is very similar to the Kowa BDII 6.5x32 -- slightly sharper in the center I'd say.
But if you want super sharp to the edge -- the Komz 7x30 IF model is the way to go.
A lot depends on the individual accomodation however. I can take a pic through it tomorrow.
I might make a longer thread one day about the many wide angle binos I collected so far but I rarely find the time for long posts.
The wide angle 7x50s are better at the edge. Of the smaller models, interestingly my oldest, the 6x18 "Helios" (probably not related to the Russian brand) pocket bino has one of the best corrected edges and is as wide as the Kowa or Komz. I am seriously considering having the prisms and lenses coated. It would of course be much more expensive than what I paid for it but it would make for an almost unbeatable wide angle pocket bino.
Look at the second picture at the far left -- how sharp the boat shed still is. This beats almost every wide angle bino I own.

 

[William Lewis]

No. I think it is very similar to the Kowa BDII 6.5x32 -- slightly sharper in the center I'd say.
But if you want super sharp to the edge -- the Komz 7x30 IF model is the way to go.
A lot depends on the individual accomodation however. I can take a pic through it tomorrow.
I might make a longer thread one day about the many wide angle binos I collected so far but I rarely find the time for long posts.
The wide angle 7x50s are better at the edge. Of the smaller models, interestingly my oldest, the 6x18 "Helios" (probably not related to the Russian brand) pocket bino has one of the best corrected edges and is as wide as the Kowa or Komz. I am seriously considering having the prisms and lenses coated. It would of course be much more expensive than what I paid for it but it would make for an almost unbeatable wide angle pocket bino.
Look at the second picture at the far left -- how sharp the boat shed still is. This beats almost every wide angle bino I own.

They look nifty. Might be a bit of field curvature making the boat on the left sharp. If you see the branches in the foreground on the LHS are also quite sharp but the boats to the right are not. Field curvature usually brings things that are closer to you into sharper focus the closer they are to the edge of the field.

 

[Binocollector]

I know but I tested it not only on those boats. It is sharper at the edge than any of the wide angle Japanese porros. Also sharper than the Komz 6x24.

 

[Binocollector]

And where the Komz and many other wide angles also have some astigmatism which cannot be focused out at the edge, on that tiny Helios it's really just some slight curvature and any blurriness can be focused out. Really makes you think what the actual progress during the last 80 years really was except for the coatings.

 

[Binocollector]

I took a few more pics to compare curvature and pincushion on some of the EWA models.
The most similar are indeed the Kowa and Komz. But the sweet spot is slightly larger on the Kowa, unlike I remembered.
Interestingly - the J-B93 miniature bino, 6x25, 11.5°, is the most comfy for me while panning and scanning and has some of the highest pincushion distortion.
On the Komz and Kowa it's very low.
J-B93 "mini":

Komz:

Kowa:

 

[Binocollector]

I guess I should have posted that in the "curvature and distortion" thread. I really need to do a more sophisticated comparison of all of these, like by using a tripod and not snapping pics through the kitchen window.