8X32 FL vs 8X42 FL (1 Viewer)

Arthur and Leif,

Probably "field flatteners " is a misnomer for these things since the binoculars that use them still have some field curvature. A diagram in an old Fujinon FMT-SX brochure shows a reduction in "distortion" and edge "astigmatism". I think most of the edge softness that can't be corrected by refocusing is astigmatism. It turns star points near the edge into lines, parallel to the edge of the field on one side of focus, perpendicular on the other side and little crosses at best focus. That's what I see near the edge of the field in the Zeiss 8X42 FL.

As to distortion, I can't see much in the flat field binoculars I use, and it varies from some pincushion in a Pentax 10X50 PIF to very slight barrel in a Fujinon 8X30 FMT-SX. It's true I haven't noticed any flat field binoculars with AFOV's above 65 degrees, but it seems that almost all "wide field" binoculars now have fields that fall between 60 and 65 degrees. Binoculars with 70 degree fields like the Nikon EII and Swift Audubon (and Arthur's beloved Leitz Binuxit) have unfortunately become rarities.

Henry

Yep,

The Nikon SE, with "field flatteners", has much less astigmatism towards the edges than do binoculars without them, such as all the Ultravids, Zeiss FLs, Swaros etc., and like Leif, I also don't think it is just because of an element which reduces curvature.

The flattest field I have seen in binoculars, with the least amount of both curvature and astigmatism, is in the Canon 15x50 IS UD, which also has a "field flattener".

Kimmo

kabsetz said:

Yep,

The Nikon SE, with "field flatteners", has much less astigmatism towards the edges than do binoculars without them, such as all the Ultravids, Zeiss FLs, Swaros etc., and like Leif, I also don't think it is just because of an element which reduces curvature.

The flattest field I have seen in binoculars, with the least amount of both curvature and astigmatism, is in the Canon 15x50 IS UD, which also has a "field flattener".

Kimmo

Click to expand...

When comparing the Nikon SE to Ultravids, FLs, and ELs you need to consider the size of the true field. The image quality in the Ultravids, FLs, and ELs have better image quality at the point where the EL stops than at the edge of the field in the Ultravids, FLs and ELs.

The true field of the 10x42 SE is 314 feet at 1000 yards
The true field of the 10x42 Ultravid, FL and EL, is 330 feet at 1000 yards.

If you look at an object 157 feet (1/2 of the field of the SE) from the center of the field in the Ultravid, FL and EL it will look better than the same object at 165 (1/2 of the field of the Ultravid, FL and EL) from the center of the field in the Ultravid, FL and EL.

Rich

Recently I borrowed a friend’s new Zeiss 8X32 FL with the idea of doing a detailed comparison of it, the Nikon 8X32 SE and the Zeiss 8X42 FL. Unfortunately it became apparent after resolution and star testing with the magnification boosted to 40X that this particular 8X32 FL was not a very strong sample. The defects were not severe, but the left side had some astigmatism and the right side had slightly decentered optics. It would have been at a clear disadvantage in an overall comparision to defect free samples of the other two. So what I am posting now are just the observations I an pretty confident are not affected by the sample defects.

The eyecups on the 32mm FL have been changed compared to the early 42mm FL cups. The rim is now wider and IMO more comfortable. Zeiss-USA says the new cups fit the 42mm models, but are not yet available as a separate part in the US. I’ll be getting a pair as soon as they are available. If any other 42mm FL owners are interested you will need to get a new larger rainguard at the same time. I suppose the newest 42mm’s are already supplied with these.

The 32mm FL has more elaborate internal baffling between the focusing element and the prism housing compared to the 42mm. I don’t know if this reflects different baffling requirements for the 32mm or if it is an improvement designed to increase contrast that will be incorporated in the 42mm’s. A little flare can be seen under difficult lighting conditions. In the 8X32mm this occurs at close focus when the focusing element has been moved far enough back to expose reflections from the edge of the objective cell to the eye. Oddly enough it happens for exactly the opposite reason in the 8X42mm FL. At longer focusing distances in the 8X42 the focusing element moves far enough forward from the prism housing for reflections from the edge of its cell to become exposed to the eye. Flare is really not much of a problem in either and is highly dependent on the eyecup length chosen.

Light transmission is very high in the 8X32 FL, only very slightly below the 8X42. I find Zeiss claim of about 92% transmission quite credible. This is a considerable achievement given the disadvantage of the Schmidt-Pechan prism. Sometimes I could see no difference at all in brightness between the two (or the Nikon SE), however after switching back and forth quickly many times I found the majority of the time the 8X42 FL and 8X32 SE looked slightly brighter in bright sunlight. Of course in dim light the 8X42 was much brighter than the other two. I could detect no difference in color transmission between the two Zeiss.

Correction for longitudinal chromatic aberration appears to be just as good in the 32mm FL as in the 42mm. Even with the magnification boosted to 40X the center of the field is remarkably free of color friinging, with fringes about 1/4 the width of those in the Nikon 8X32 SE.

I measured center of the field resolution of the left (astigmatic) side of this pair of 8X32 FL’s at 5.2”. The right side measured about 4.2” which is certainly closer to what could be expected from a defect free pair. Under the same test conditions the Nikon SE measured about 3.8” and the 8X42 FL about 3.2”. All of these figures when multiplied by 8X are better than eyesight resolution, but worse than expected measured resolution, even if it is still better than eyesight usually means something is wrong that may be visible. In this case star testing revealed astigmatism in the left barrel, and in use that side looked slightly soft. I've found that the the 8X42 FL looks a tiny bit sharper than the SE in the center of the field. I doubt that this is related to actual resolution, but more likely is a benefit of lower longitudinal chromatic aberration. Off axis sharpness in the 8X32 FL holds up a bit better than the 8X42 FL. It falls about midway between the 8X42 FL and the Nikon SE. Toward the edge of the field star points in both Zeiss become astigmatic changing from points into lines running parallel to the field edge, but the length of the line is about half as long in the 8X32. In the Nikon SE stars at the edge of the field remain mostly points with only slight elongation.

One interesting thing I noticed is that the apparent or subjective field of the 8X32 FL is actually no larger at all than the apparent field of the 8X42FL even though the Zeiss spec for real field is 5m wider for the 8X32. I checked this by holding one eyepiece of each binocular to each eye simultaneously and comparing the fieldstop sizes. The left side field stop of the 8X32 matched the 8X42 exactly and the right side was actually slightly smaller (different sized field stops in the same binocular is something I don't like to see since it can indicate different magnifications). At first I assumed the spec for the 8X32 real field must be wrong, but when I measured real field with a measuring tape placed at 10m I found the 8X32 did have a slightly wider real field. The explanation is pin-cushion distortion. There is more of it in the 8X42. That causes an increase in magnification at the edge of the field which reduces real field compared to a more distortion free eyepiece of the same apparent field. The Nikon SE has less distortion than either of the Zeiss, barely any at all.

One last thing, which I mentioned earlier in my quick store impressions. The objective spacing of the 8X32 FL is 7mm narrower than the 8X42FL at the same IPD. Believe it or not that small difference creates a noticeable illusion of higher magnification in the 8X32 compared to the 8X42 at close distances.

I suspect my household will be acquiring a pair of 8X32 FL’s. My birder wife usually considers binoculars a necessary (or not so necessary) evil. She found herself so smitten with these that she didn’t even flinch very much when I told her the price and actually mulled over buying a pair herself, a first in twenty years of marrage.

Zeiss 8x32 FL "sweet spot"

Henry,
As I mentioned in my comments on another thread, I find the "sweet spot" of the Zeiss 8x32 FL to be small compared to my preferences and to the Leica 8x32 BN and Leica 8x32 Ultravid. This finding is disappointing to me, because these are otherwise, optically, the most outstanding of midsize roofs. Yet if not for their exceptional close focus, excellent eye relief, and exceptionally low (52mm) minimum interpupillary setting, I would probably opt for the Leica 8x32 Ultravid over the FL because I so much enjoy how well the Ultravid retains its sharpness outside the center of the field (and I'm not bothered by CA unless I am actively looking for it).

At the risk of reinitiating the whole Zeiss FL sweet spot controversy, I would really appreciate yours or others' careful description of field sharpness in the 8x32 FL. I've been using the Zeiss 8x32 FL for several hours a day, every day, for the past several weeks in the course of doing fieldwork for a grassland bird study and can testify that they are optically outstanding and very comfortable to use (even one-handed). In the heat of such work, the size of the sweet spot is not at all bothersome--in fact, I find nothing wanting with regard to optical performance, in contrast to most other binoculars of similar size and weight. One nice feature of the FL that I have not seen others mention, is that the diameter of the ocular housing/eyecups is fairly large, so they do a good job of blocking lateral light when used with eyeglasses.

On the other hand, I've looked at two 8x32 FL units and found them to be essentially identical with regard to having considerably more resolution-robbing distortions (mainly astigmatism I think) outside the center of the field than the Leicas and others. As a consequence, I am completely baffled by some reviews I have seen extolling the edge-of-field sharpness of the 8x32 FL (much as I was baffled by some early reviews of the Leica 8x42 Ultravid proclaiming that it has very low chromatic abberation and exceptional edge of field sharpness, neither claim of which I find to be true). The Zeiss seem to be a bit more finicky than some others with regard to centering one's eyes on the exit pupil to get the best quality view, and the optics of my glasses does not seem inteface with them as well as with other binoculars when it comes to off-axis viewing, but I do not think these factors account for my perception that the Zeiss 8x32 FL sweet spot is on the small side.

--AP

Alexis, I'm mystified by your post. On the one hand you say about the 8x32 FL that "I find nothing wanting with regard to optical performance..." On the other hand, you complain about a "small sweet spot." So they are "wanting!" You seem to have an unresolved ambivalence.

Alexis Powell said:

Henry,
As I mentioned in my comments on another thread, I find the "sweet spot" of the Zeiss 8x32 FL to be small compared to my preferences and to the Leica 8x32 BN and Leica 8x32 Ultravid. This finding is disappointing to me, because these are otherwise, optically, the most outstanding of midsize roofs. Yet if not for their exceptional close focus, excellent eye relief, and exceptionally low (52mm) minimum interpupillary setting, I would probably opt for the Leica 8x32 Ultravid over the FL because I so much enjoy how well the Ultravid retains its sharpness outside the center of the field (and I'm not bothered by CA unless I am actively looking for it).

At the risk of reinitiating the whole Zeiss FL sweet spot controversy, I would really appreciate yours or others' careful description of field sharpness in the 8x32 FL. I've been using the Zeiss 8x32 FL for several hours a day, every day, for the past several weeks in the course of doing fieldwork for a grassland bird study and can testify that they are optically outstanding and very comfortable to use (even one-handed). In the heat of such work, the size of the sweet spot is not at all bothersome--in fact, I find nothing wanting with regard to optical performance, in contrast to most other binoculars of similar size and weight. One nice feature of the FL that I have not seen others mention, is that the diameter of the ocular housing/eyecups is fairly large, so they do a good job of blocking lateral light when used with eyeglasses.

On the other hand, I've looked at two 8x32 FL units and found them to be essentially identical with regard to having considerably more resolution-robbing distortions (mainly astigmatism I think) outside the center of the field than the Leicas and others. As a consequence, I am completely baffled by some reviews I have seen extolling the edge-of-field sharpness of the 8x32 FL (much as I was baffled by some early reviews of the Leica 8x42 Ultravid proclaiming that it has very low chromatic abberation and exceptional edge of field sharpness, neither claim of which I find to be true). The Zeiss seem to be a bit more finicky than some others with regard to centering one's eyes on the exit pupil to get the best quality view, and the optics of my glasses does not seem inteface with them as well as with other binoculars when it comes to off-axis viewing, but I do not think these factors account for my perception that the Zeiss 8x32 FL sweet spot is on the small side.

--AP

Click to expand...

Alexis,

I did make some measurements of the fall off in off-axis sharpness in the Zeiss 8X32 FL I recently borrowed. I do this by placing a measuring tape perpendicular to the line of sight and at a distance from my pair of Nikon 8X32 SE's so that 60" on the tape exactly spans their 60 degree AFOV. So each inch on the tape equals about 1 degree of apparent field for any 8X binocular at that distance. Using one eye I try to judge how far from the center of the field something close to center sharpness is maintained. Admittedly its a subjective test, only good for comparing a few binoculars on a particular day. The actual numbers I get seem to vary from one time to another for a particular binocular, perhaps influenced by varying eye strain on different days, but the ranking of binoculars seems to stay the same.

I compared the 8X32 FL, 8X42 FL and 8X32 SE. I should mention that this particular 8X32 FL had slightly decentered optics in the barrel I tested, so its results could be a little worse than a perfect pair. To my eye on that day about 90% of center sharpness was maintained by the 8X42 FL to about 13 degrees off-axis, the 8X32 FL 16 degrees and the 8X32 SE 20 degrees. The SE result was particularly good on that occasion, perhaps reflecting better than usual focus accommodation in my eye on that day. Based on that result and other comparisons I would say the off-axis performance of the 8X32 FL is actually pretty good compared to binoculars which don't have the advantage of field flatteners like the Nikon SE and LX/HG. It appears to be very close to the performance of the Swarovski 8.5X42 EL. In a brief comparison in a store I thought it was better off-axis than an 8X32 EL. Unfortunately I haven't yet seen an 8X32 Ultravid and haven't seen a 8X32 Trinovid in so long that I really can't make a comparison to it. I agree with you that most of the off-axis fall off in sharpness in the FL's is astigmatism rather than field curvature which you can easily determine by looking at stars and refocusing.

Henry

Alexis and Henry,

Some time back, I did tests very similar to Henry's, but I had a relatively coarse spacing of the test target, having it at 0, 10cm, 20cm etc. off-center at 10 meters. Here I had the FL, Swaro EL and Ultravid 8x32's. I did not get reliable differences in sweet spot sizes, but the FL had considerably better performance far off-center, 40cm and further. In the very center, the Ultravid (in these particular specimen) was slightly sharper than the other two, but at 10 and 20cm off-center all three measured identically. The 8x42 FL I have measured similarly, but at a different time. My notes show results very similar to the three smaller ones, with the exception of even better center field resolution (but not by much) and edge performance more akin to the Swaro and the Leica, a clear step down from the 32mm FL.

Although I did not do Henry's splendid reflected light comparison to determine whether or not the Ultravid's optics have been reconfigured, I have a strong suspicion that they are unchanged from the 8x32BN except for improved contrast, transmission and a slightly more neutral color balance.

In field use, I did not find the 8x32 FL's nor the Ultravid's sweet spot size to be an issue, and from Alexis' post, I get the impression that he didn't either. Sometimes too much testing makes it more difficult to enjoy good gear in the field, it seems.

Kimmo

overall impressions still valid?

Now that the models have been in longer and widerspread use, I wonder whether the impressions gained from early units still hold. Zeiss in particular has a history of not too good quality control at the outset. But then, there might also be possible relaxations (in any brand) after the critical testing reviews have all been written?

So I wonder whether the standards measured earlier are still approximately the same now. In particular, I am curious about the results of 8x32 FLs which, at the time of Henry's comparison, had some flaws in the tested sample.