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Tests of the Zeiss 8x54 HT (1 Viewer)

henry link

Well-known member
I’ve finally finished assembling star-test and other images from the Zeiss 8x54 HT I spent some time with. There are too many images for one post, so I’ve decided to make 5 separate posts. Anybody with comments please wait until all 5 are up. Thanks.

The first two images are star-test sequences of the left and right sides of the Zeiss 8x54 HT at full aperture. The five images go from left to right, outside of focus to best focus to inside of focus

Even by the lax standards applied to binoculars these are spectacularly bad star-tests. The spherical aberration is off the chart (2 waves or worse?). In addition there is some coma (probably from de-centering the eyepieces for collimation purposes), the right side has some astigmatism and the left side has some sort of odd spiky obstruction coming up from the bottom (I think the angle is wrong for the prism edge).
 

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henry link

Well-known member
The next images are the same binocular stopped down to 22mm. The astigmatism is almost gone and the spike has disappeared. Spherical aberration is better corrected, but only to maybe ½ wave. There is some problem with the left side photos. They should not be so soft. Possibly a thin cloud I didn’t notice moved over the sun while I took them. My memory is that the left side was slightly better corrected for SA when stopped down than the right side.
 

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henry link

Well-known member
These are images of one side of my 8x56 FL for reference. The left image is full aperture and the right image is stopped down to 22mm. Full aperture SA might be around 1 wave and stopped down to 22mm around ¼ wave, both much better than the HT. I should mention that the full aperture SA of the FL may look better than the HT, but it’s also high by binocular standards.
 

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henry link

Well-known member
These are images of a target I use to evaluate lateral color. FL is on the left, HT on the right. At the distance these were taken the centers of the white bars are separated by about 1º of AFOV. Neither image is quite perfectly centered, but they’re close enough to show how much worse the lateral color near the field center is for the HT compared to the FL. I’ve come to think that the excessive lateral color is just as big or a bigger problem than SA for the formation of a sharp image in the center field of the HT. Only a little pupil displacement, like what happens continually when hand holding, will cause lateral color to appear right in the center, smearing the image. One of the first things I noticed about the HT is that pupil centering is hypercritical for even a half decent image.
 

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henry link

Well-known member
Finally, this is an image of a white background, illuminated by northern sky light, as seen through the objective ends of the HT (left) and the FL. I think you can notice the slight yellow/green bias of both binoculars. This isn’t a strong tint, the eye quickly adjusts, but it’s not state of the art neutral either. In use the HT looks slightly more neutral to me than the FL, and to my surprise, the light transmission of the HT does appear a bit higher than the FL in normal use. I would have guessed around 5% higher just from looking.

Examining just one specimen of a binocular leaves open the question of whether any deficiencies are sample defects or design flaws. I’ll go out on a limb and say that I’m sure the astigmatism in the right side and the odd spike in the left are sample defects since each is confined to a single telescope, but I strongly suspect that the high levels of SA and lateral color were incorrectly judged by the designers to be low enough to do no visible damage to the image. I’m sorry to say the damage is visible and the result is that the 8x54 HT fails to bring light to a truly sharp focus, the most fundamental task of a binocular. I thought this might be my next purchase and it could have been if Zeiss had just made a lighter 54mm version of the 8x56 FL with improved light transmission.

Henry Link
 

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james holdsworth

Consulting Biologist
''but I strongly suspect that the high levels of SA and lateral color were incorrectly judged by the designers to be low enough to do no visible damage to the image. I’m sorry to say the damage is visible and the result is that the 8x54 HT fails to bring light to a truly sharp focus, the most fundamental task of a binocular.''


If this is really true, then Zeiss needs new designers ASAP - maybe someone from Zen-ray is available....;)

Seriously though, are we to believe that Zeiss throws together this model, with optical flaws and says ''good enough'', when the 42 mm HT's and the entire Conquest line have tested so well, including the 56 mm line?
 
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typo

Well-known member
Henry,

Many thanks for the analysis. I confess I still struggle to correlate defocussed stars with normal observation but I must congratulate you on the excellent images that help me get a step closer.

You mention the lack of sharpness, did you estimate full and reduced aperture resolutions?

David
 

statestat

Well-known member
This is one the best examples of a picture being worth a thousand words.

The star test is so revealing, bino makers should include them with each pair like
a test target some high end firearms makers provide. The lateral color target interests me greatly. It looks like strips of masking tape, will you share the design, I would like to evaluate/compare some bins. Very good thread, sad results though.
 

henry link

Well-known member
Thanks Bryce.

Typo, I have to be away from the computer till Sunday. I'll get back with you about resolution measurements.

Statestat, Not much to it, 1/2" white plastic tape wrapped at 2" intervals around a 6' piece of pine lattice, painted black.

Henry
 

Holger Merlitz

Well-known member
Seriously though, are we to believe that Zeiss throws together this model, with optical flaws and says ''good enough'', when the 42 mm HT's and the entire Conquest line have tested so well, including the 56 mm line?


That would depend on what happens next: Are there going to be more samples of this "quality" coming up? Or will Zeiss postpone the production of further samples, followed by a re-introduction 6 months later?

Wait and see - and better be cautious when buying one of these binoculars in the near future.

Cheers,
Holger
 

ronh

Well-known member
Henry,

Thanks for the hard work, you poor slob, and interpretation of the star test and all the reports. I hope they are of use to Zeiss, as they are to us. I guess only time will tell.

A similar test of a 42mm HT would be of great interest. It has received only glowing reports so far, but I have seen no such tests as yours.

Ron
 

Binastro

Well-known member
Thanks Henry for the excellent photos and interpretations.

I wish I could show you the same results for my own eyes, which show dismal out of focus star patterns.
At least one eye seems completely out of alignment.

Angenieux do indeed include individual graphical results at least with each 8 x24 binocular.

Despite this an ancient Pentax 8 x 24 is optically and mechanically far better.
 
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henry link

Well-known member
Henry,

Many thanks for the analysis. I confess I still struggle to correlate defocussed stars with normal observation but I must congratulate you on the excellent images that help me get a step closer.

You mention the lack of sharpness, did you estimate full and reduced aperture resolutions?

David

David,

I’m back at the computer. I didn't photograph the resolution tests, but here are a couple of extreme crops of the center cross of my CA target, FL on the left and HT on the right, both at full aperture. They might give you an idea of the differences visible between the FL and HT on the USAF 1951 Resolution Test Pattern at very high magnification. Both show an odd green fringe at best focus, much worse in the HT. A green fringe doesn’t make much sense at best focus where you expect green to be a focused color, but there it is. I suspect it has something to do with spherochromatism causing green from the outside part of the objective to swing very far out of focus compared to green from the central part, but that's pure speculation. The elements of the USAF 1951 chart viewed through the HT at high magnification look like gray/green bars surrounded by a green haze. The FL shows some of the same effect, but much less. At high magnification most binoculars at best focus show a red or purple fringe impinging on dark gray bars.

The measured resolution of the HT at full aperture on the USAF chart is 3.5”. That may not seem too bad for a binocular even though the high magnification image looks terrible. However, that raw number is actually poor for a 54mm aperture. It corresponds to 189/D (with D the diameter of the objective in millimeters). The 8x56 FL measured at the same time was 2.7” (151/D), better but not that great either. The best binoculars I’ve measured come in around 125/D at full aperture, within spitting distance of the best low aberration telescopes measured on the same chart (115/D).

Unfortunately I neglected to measure the stopped down resolution of the HT, but given the appearance of the 22mm star-test I would expect it to be somewhat worse than the FL, maybe around 135-140/D (with D=22mm), around 6.2”.

Those results don’t seem to me to explain why, for my eyes, the HT had poorer resolving power in bright light than the FL at 8x. You may know that I don’t place much confidence in resolution comparisons of binoculars at low magnification using the USAF chart. I don’t think it makes a good resolution target at low magnification because the smallest resolvable elements become too tiny and crammed together. For my eyes (around 90” acuity using a line pair per millimeter chart like the USAF 1951) there is virtually never a consistent repeatable difference in resolution among decent quality binoculars of the same magnification with the USAF chart. However, when I compared the FL and the HT several times tripod mounted at 8X I found the HT resolved about 1 element less (12.4”HT vs 11”FL), the equivalent of dropping my eyesight acuity from 88” to about 100”.

My speculation is that lateral color plays a large role in that difference, but would not be significant for boosted resolution because the area subtended by the smallest resolvable element, when perfectly centered at high magnification, is so tiny that it fits comfortably with the small area free of lateral color in the HT. At high magnification and full aperture spherical aberration dominates.

It appears that the oddities of the aberrations in this binocular create a rare instance where the resolution visible on a lp/mm chart at low magnification is poorer than would be predicted by the true resolving power of the instrument.

Henry
 

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typo

Well-known member
Henry,

Thank you very much for the further analysis. There are a few things there I'd like to explore but I probably won't have a chance to do it this evening.

Cheers,

David
 

David in NC

Well-known member
Question:

UNTIL THIS IS FIXED-DOES THIS MEAN WE ARE GOING TO HAVE TO START THE HT "COUNTDOWN /COUNTUP CLOCK" AGAIN???

3:) 3:) 3:) 3:) 3:)
 

henry link

Well-known member
I doubt that anybody at Zeiss is losing any sleep over this thread. These are for hunters to use in low light. I don't think many hunters will notice anything wrong, especially at very low light levels when eyesight acuity is extremely poor.
 

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