disappointing sharpness with the 10x42 FL (1 Viewer)

Hello

I have read the review of the Zeiss FL by Kimmo Absetz on the Alula web site
( http://www.alula.fi/GB/index.htm ).
According to my comparatively small experience with binoculars, I fully agree with ALL his statements.
The point that holds my attention is that the 10x binocular he tested was a bit less sharp than the 7x and 8x ones. A few comments on other binocular forums about the 10x42 FL led to the same conclusion when compared to the equivalent Leica or Swarovski binoculars.

Since the very first glance through my 10x42 FL, I suspect there is something wrong in my binocular, without being able to know what. I have spent a lot of time, until madness, testing the FL and my previous Zeiss Dialyt side by side, tripod mounted, at high contrast targets, low contrasts targets, with a booster ( in fact a 5x monocular ), without the booster, etc…
Here are the results :
- in sunlight conditions there is no difference at all in sharpness between both binoculars.
- in moderate or low light conditions, there is no difference in sharpness on high contrast objects like branches against the sky. But on complex surfaces like the bark of a tree, or very small irregularities in a wall, the Dialyt is better. Unfortunately (or fortunately ? ) the eyes seem attracted by high contrast objects, so every time I wanted to test the binoculars, I was instinctively looking at high contrast objects, and couldn’t see any difference. It took me two months before I could confirm the difference in sharpness on complex and moderate contrast objects.
- This difference in sharpness varies from one day to another, even in identical lightning conditions. This suggests that my eyes are also involved, and perform better some days than the others.
- To my eyes, test targets are nearly pointless to evaluate sharpness. I can achieve the same resolution with both binoculars, that is precisely 10 fold the resolution of my naked eye. But the lines easily resolved appear sharper with the Dialyt.
- I am unable to relate sharpness to the resolution obtained with a booster. I also have a cheap 10x40 binocular whose resolution is barely improved by the booster, however its sharpness is better than the FL !
- The star test with the booster shows poorly collimated patterns, so perhaps I have another lemon. But I think there is also spherical aberration, which is probably a designed feature.

Now, is this lack of sharpness visible with hand held binoculars ? Not really, but in some situations the good focus is difficult to find, I have to concentrate and turn very carefully the focus wheel before I could find the best image. This never occurs with my other binoculars, in which the image snaps nicely into focus.

Finally, I have cut 2 rings in a black piece of plastic in order to stop down the aperture to 39 mm. The improvement is very small, but I think that focusing is easier, so I wonder if I will keep these aperture stops all the time. On the night sky, I can see flares around bright stars with the 42 mm aperture that almost disappear with these little stops.

In conclusion, I still don’t know if this lack of sharpness is due to :
- my eyes, which would be better with a 3.9 or a 4 mm exit pupil than with a 4.2 mm exit pupil
- my binocular because the objectives are badly centred
- the 10x42 FL, because for this model the designers made a trade-off between sharpness and other properties.

What do you think about this strange story ?

Jean-Charles

My swift roofs are like that. Sometimes the image is clear bright and sharp but depending on the lighting and background sometimes the images are not as sharp. I have a quick focus but have to fuss around to get it right sometimes.

My Zeiss 10x42FL gives bright high contrast images. I got to compare two Zeiss 10x42 FL at the store before I bought one. I thought there might be a very small difference in the image between the two FLs.

I hope you can take your FL to a dealer and compare it to two or three other 10x42 FLs. If yours doesn't give as good images I would certainly see if Zeiss is willing to fix it or give you a new pair.

Good luck,
Rich

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Jean Charles,

I made several experiences of sample variation when Zeiss introduced new series of sport optics. Therefore I suspect that while the construction of the Zeiss optics are among the best available nowadays there´s a lack of quality controll in the production especially when the serie is new. The issue with the focus knob of the 42 FLs which you can read about in this forum sounds like something similar. A perfect collimated 10x42 FL should have more contrast and brightness than the (10x40?) Dialyt, no CA in the center and has neutral color without yellow color cast. If possible I would compare your 10x42 FL with some other 10x42 FLs to find out some more results. I guess this could be a case of warranty and I wouldn´t hesitate to contact Zeiss.

Steve

It is hard to do adequate QG when you are trying to satisfy anxious dealers and consumers. Most companies just crank them out to meet demand and deal with the occasional problems later.

Jean Charles,

I've been able to star test five samples of the Zeiss FL's: three 8X42's and two 8X32's. Of these only one pair of 8X42's was completely defect free, and one 8X32 had only slight decentering of one objective. The other two 8X42's had significantly decentered objectives in both barrels and one 8X32 had decentering in one barrel and astigmatism in the other. All of these came from early production, within a few months of the introduction of each model. I doubt that Zeiss is the only company guilty of allowing units with these kinds of defects to leave the factory. I suspect all the optics firms, even the high end ones, rely on the low magnification of binoculars to allow them to apply some fairly lax standards when it comes to optical defects. Since a defect has to be pretty serious to be clearly visible at 10X or less, why go to the expense of completely elliminating something that is probably not going to be visible anyway.

I've noticed that decentered objectives don't seem to cause a very obvious problem in the image, but perhaps eventually there is a price to pay in viewing comfort or in consistency of image quality as the eye tires, especially at 10X. I used a pair of 8x42's with decentered objectives for about three weeks and never felt completely comfortable with them.

The astigmatic barrel in the 8X32 had actual resolution on my chart of about 5.2 arc seconds compared to about 4 arc seconds for the other side (with the magnification boosted to 40X), but thanks to the forgiving nature of low magnification even that defect was barely visible to me as only a very slight softening of the image at 8X with the binocular mounted on a tripod. Hand holding I really couldn't see a problem, but I suspect that particular binocular might eventually be fatiguing to use.

I've now seen enough of these defects so that I've decided to never buy another expensive binocular, except from a local dealer who will allow me to star test a pair before purchase.

Henry

P.S. I think the objectives of the 42mm FL's are unusually fast, perhaps around f/3.5. The 10X40 Dialyt is probably closer to f/4. That might be part of the reason you prefer the image with the objective stopped down, since that would bring the focal ratio of the FL closer to the Dialyt.

I was about to write a somewhat comprehensive response earlier today, but went birding instead. Now I'm glad to see that Henry has done it already, so I'm saved much time. I would only add a couple of comments/opinions.

Firstly, in my experience especially astigmatism tires the eye noticeably, even when its effects on measured resolution lay "comfortably" below the threshold of the eye. Secondly, other optical aberrations such as decentered optics and exessive spherical aberration, reduce not only resolution but also contrast, and I suspect this is what you are reacting to. The human eye can see that one image is better than the other even when the differences show up as measured resolution figures significantly (at least up to twofold) higher than what the eye is capable of resolving on its own. I think that the optical companies have been seduced to think that as long as the binocular resolves better than the human eye theoretically can, everything is okay and no one should complain. Alas, this is not so.

Kimmo

Is there an easy way for the average person to check a new pair of binoculars for astigmatism and decentered objectives? I know how to do a crude check for alignment, but I'm clueless on these other things.

Thanks,

Bruce

Rich N said:

I hope you can take your FL to a dealer and compare it to two or three other 10x42 FLs. If yours doesn't give as good images I would certainly see if Zeiss is willing to fix it or give you a new pair.

Click to expand...

hinnark said:

If possible I would compare your 10x42 FL with some other 10x42 FLs to find out some more results. I guess this could be a case of warranty and I wouldn´t hesitate to contact Zeiss.

Click to expand...

Rich and Steve : you are surely right, I’ll know if my unit is defective not by questioning other owners, but only by comparing it to several 10x42 FLs. However, this will require a long trip to go to such a Zeiss dealer (I believe that Leica is far more present here).


Henry Link,

I was aware of your star tests on three 8x42’s, but not on the 8x32’s. This is very interesting. Finally, it is possible that my unit lies into the tolerances defined by Zeiss, even if slightly better samples can be found. This raises the question of to what extend a defect must be considered as unacceptable.

henry link said:

I think the objectives of the 42mm FL's are unusually fast, perhaps around f/3.5. The 10X40 Dialyt is probably closer to f/4. That might be part of the reason you prefer the image with the objective stopped down, since that would bring the focal ratio of the FL closer to the Dialyt.

Click to expand...

I confirm now that I prefer the 10x42 stopped down to 39 mm. I will be happier for the moment with a perfect 10x39 rather than a very good 10x42.
It’s not directly related to the focal ratio of the binocular, in my opinion. This tip reduces the amount of optical aberrations either in the binocular because of the aperture stop, either in my eyes because of the smaller exit pupil.

kabsetz said:

I think that the optical companies have been seduced to think that as long as the binocular resolves better than the human eye theoretically can, everything is okay and no one should complain. Alas, this is not so.

Click to expand...

Kimmo,

You suggest that even high end companies have excessively large tolerances, this is really disappointing.

Jean-Charles

Bruce,

A test for astigmatism would be to preferably mount the binocular on a tripod and then try to look at an artificial star such as a glitter point (with one barrel at a time). If the best focus image is cross-shaped rather than a relatively round blob (we cannot expect perfect Airy discs with binoculars, although I have seen that too), you have astigmatism. If oout-of-focus ring patterns are elongated into ovals, with the long axis changing directions when you go through focus to the other side of focus (from too near to too far or vice versa), you have astigmatism. For decentering, out-of-focus diffraction ring pattern which has an eccentrically placed bright spot and usually eccentric brightness distribution in the rings is the indication. I have found that decentering can be evaluated also with any white speck against a black or dark background. If you begin to defocus, if the white of the speck begins to "spill" very obviously off to any one side, you have decentered optics. The problem with this latter method is that I have not done enough trials to determine how sensitive it is. Therefore I cannot say what level is acceptable nor, indeed, whether it is at all likely for you to find a binocular with perfect symmetry of the pattern.

Jean-Charles,

Carefull as I try to be with words, I'd avoid saying "excessively large tolerances" and would prefer something like "tolerances greater than what we'd wish to see in a perfect world." What is excessive for you and me may very well be perfectly acceptable for someone else - even if that someone is not working for the optical company. In all of this, we must also keep in mind that tighter tolerances equal higher production costs and slower production - top-class apochromatic refractors are hand-figured and individually collimated while being mechanically much simpler than any of the binoculars or even spotting scopes we are discussing on this forum. Also, the manufacturers hopefully realize that tighter tolerances mean a higher ratio of satisfied/unsatisfied customers.

Kimmo

kabsetz said:

Bruce,

A test for astigmatism would be to preferably mount the binocular on a tripod and then try to look at an artificial star such as a glitter point (with one barrel at a time). If the best focus image is cross-shaped rather than a relatively round blob (we cannot expect perfect Airy discs with binoculars, although I have seen that too), you have astigmatism. If oout-of-focus ring patterns are elongated into ovals, with the long axis changing directions when you go through focus to the other side of focus (from too near to too far or vice versa), you have astigmatism. For decentering, out-of-focus diffraction ring pattern which has an eccentrically placed bright spot and usually eccentric brightness distribution in the rings is the indication. I have found that decentering can be evaluated also with any white speck against a black or dark background. If you begin to defocus, if the white of the speck begins to "spill" very obviously off to any one side, you have decentered optics. The problem with this latter method is that I have not done enough trials to determine how sensitive it is. Therefore I cannot say what level is acceptable nor, indeed, whether it is at all likely for you to find a binocular with perfect symmetry of the pattern.

Jean-Charles,

Carefull as I try to be with words, I'd avoid saying "excessively large tolerances" and would prefer something like "tolerances greater than what we'd wish to see in a perfect world." What is excessive for you and me may very well be perfectly acceptable for someone else - even if that someone is not working for the optical company. In all of this, we must also keep in mind that tighter tolerances equal higher production costs and slower production - top-class apochromatic refractors are hand-figured and individually collimated while being mechanically much simpler than any of the binoculars or even spotting scopes we are discussing on this forum. Also, the manufacturers hopefully realize that tighter tolerances mean a higher ratio of satisfied/unsatisfied customers.

Kimmo

Click to expand...

Kimmo: Thanks very much for the clear and concise explanation. It'll be very helpful, as I may be ordering some new binoculars soon.

Bruce

Here is the end of the story :
A couple of weeks after my post in this thread, I sent an e-mail to Zeiss Sports Optics in Germany, questioning them about my binocular and manufacturing tolerances. They immediately replied they would like to make an inspection of the binocular, so I sent it back to my dealer.
Finally, they fixed my binocular.
No need for tests, bar targets, writings, or scientific procedures : the fixed binocular is definitely better, and on par with my two other excellent 10x40 binoculars, as far as sharpness is concerned. The right diopter adjustment is not hard to find, there is no need to guess the good focus in low light conditions, and there is no difficulty in placing the eyes when the binocular is tripod mounted.
The test the most conclusive was the night sky : at last I saw really pinpoint stars, a thing impossible before, despite I could easily resolve close double stars.
I daylight observations, I think that the contrast is also slightly improved.
To summarize, even if I’m not sure at all I’m able now to see more details than previously, the binocular is more pleasant to use. Oddly enough, the sweet spot seems smaller, but I don’t know if this is a pure illusion, or another effect of sample variation.
Finally, I still don’t know if my binocular or the binocular tested for Alula was slightly defective, or on the contrary respected the tolerances specified by Zeiss, at least I know they are willing to improve them if one asks for that.

:bounce: THE END :bounce:

Jean-Charles

An excellent result, Jean-Charles. Since I remember that you star tested your pair I would be most interested to hear about any differences you see star testing now. I can also understand if you would rather forget about that and just enjoy you "new" binoculars. ;-)

Henry

You would think if you were spending the type of money needed to purchase a pair of Zeiss optics, then they would be perfect - top quality etc. To have differences in quality other than perfect is unacceptable. In camera terms Zeiss make the best optics (in medium format anyway). Makes you wonder if they are worth the money the ask. Personaly I dont think any binocular is worth nearly a thousand pounds, Zeiss, Leica or Swaro.

Nice to hear that Zeiss was more than happy to examine your bins because you were dissatisfied and corrected them to what appears to be your satisfaction. Good job Zeiss!

henry link said:

Since I remember that you star tested your pair I would be most interested to hear about any differences you see star testing now.

Henry

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Henry,

Of course I star tested the binocular.
The left barrel, which was strongly decentered before, is now excellent, near perfection. The diffraction pattern is a very nice Airy disc with one ring. The out of focus patterns show a small amount of spherical aberration, and a very slightly decentered optics. In fact this barrel is so good that it could be a 42mm spotting scope.
In comparison, the right barrel is a little disappointing. The decentering is obvious, showing at least three arcs on one side of the Airy disc. In the out of focus pattern, the bright spot is near the outside ring. What puzzles me, is that the right barrel seemed not so bad before the correction. But I haven’t tested the binocular in the same situation, and I don’t recall exactly how it was, so perhaps it is unchanged. Even if it’s worse now, I think it is not as poor as the left barrel before the correction.

I also noticed that the collimation is excellent now, better than before.

This evening, I compared the size of the sweet spot with the Classic 10x40 : there is no problem at all, the area of best sharpness is as good as the Classic, if not better. But there is field curvature in the FL, even near the centre, unlike the Classic.
Incidentally, due to the lack of brightness and contrast, and probably some stray light in a very difficult lighting situation, for the first time the Classic looked like a toy in comparison with the FL. :eek!:

Jean-Charles

So the Dialyt that you compared against the FL the 10x42B Classic? I couldn't tell which model of bins you were comparing, the 7x42, 8x56 or whatever, in your original post, so now I have a grasp of what you're talking about...

So how did the FL exactly make the Classic look like a toy?


BTW, I currently own one of the newer P*T* 10x40B Classics and would really like to know if you thought the upgrade was currently worth it. Not interesting in buying them or anything, but since you bought the FLs are the 10x40Bs up for sale or are you retiring them as a backup pair?

I'm really curious, as I'm seriously contemplating the Ultravid 10x42 and the FL, but haven't really heard much straight comparison with the 10x40 Classic to make the 'leap of faith' (as I can't really try these all out locally).

Thanks for any insight you can relate.

The Classic/Dialyt is indeed the 10x40 T* P
Generally, it’s not a toy compared with the FL, only yesterday in a specific orientation to the light I noticed a great lack of contrast in the Classic.
I will post a complete comparative review. I’ve already written it in this forum, but it was lost in the server crash. In a few words, I think the upgrade to modern binoculars is worth it, but more because of mechanical and ergonomic issues, rather than optical ones.
I won’t sell my Classic, because I have a sentimental relation to binoculars, especially this one which was my first excellent binocular. Furthermore, it is marked “West Germany”, a real curiosity now. |;|

Jean-Charles