Ok, so I'm really just talking about a Zeiss Victory 8x42 SF that's been adapted to be a 8x32 (see attached picture). So why bother? I bothered because I wasn't happy with my newly purchase 2nd hand 8x42 SFs. My main complaint was just not quite enough resolution (for me) and contrast a bit lower than hoped. This was emphasised each time I used my fantastic 8x25 Victory Pocket, which seems to have better resolution and contrast (ahh!). So thinking like a photographer I tried a couple of things. Firstly I tried putting hoods on the binoculars to shield stray light from the objectives and that seemed to improve the contrast a bit, but obviously didn't help with the resolution. So next step was to reduce the aperture, which also has a shielding effect and bingo! This has sharpened them right up. There's still that fantastic wide field of view (not affected at all), they still appear bright in the day and the 3D effect is even more pronounced (due to increased depth of field). Most importantly for me now the resolution is phenomenal. You may be sceptical, but just try it. I first tried it with two bits of cardboard with circles cut out and stuck on and it worked. I then used a couple of old lens caps as you can see in the picture as a more long-term thing. In low light though I just take them off as brightness becomes more important. In good light in the day with the SFs at 32mm I reckon it's the best view of any binocular. I wouldn't say the same about the SFs at their normal 42mm.
-
Welcome to BirdForum, the internet's largest birding community with thousands of members from all over the world. The forums are dedicated to wild birds, birding, binoculars and equipment and all that goes with it.
Please register for an account to take part in the discussions in the forum, post your pictures in the gallery and more.
Zeiss Victory 8x32 SF!! Amazing resolution! (1 Viewer)
- Thread starter mpeace
- Start date
Vespobuteo
Well-known member
Are you familiar with Dawes' limit?
Mpease.
Welcome to the forum and thanks for your telling us about your observations.
I've tried something similar with various binoculars, and in most cased it improves contrast by reducing stray light. I haven't tried it with the SF, but I wouldn't be at all surprised if there is a noticable improvement in image quality. An improvement in contrast may well result in an improvement in apparent sharpness.
The pupil of your eye is usually the effective aperture stop and dictates the effective resolution (and brightness). In the case of the SF at least, you hope it would always exceed the magnified acuity of the eye. The samples I've seen have been pretty good, but the QC protocols when it was introduced did not guarantee it. We've been told by a member from Germany that Zeiss has subsequently introduced more stringent QC protocols.
Cheers,
David
Welcome to the forum and thanks for your telling us about your observations.
I've tried something similar with various binoculars, and in most cased it improves contrast by reducing stray light. I haven't tried it with the SF, but I wouldn't be at all surprised if there is a noticable improvement in image quality. An improvement in contrast may well result in an improvement in apparent sharpness.
The pupil of your eye is usually the effective aperture stop and dictates the effective resolution (and brightness). In the case of the SF at least, you hope it would always exceed the magnified acuity of the eye. The samples I've seen have been pretty good, but the QC protocols when it was introduced did not guarantee it. We've been told by a member from Germany that Zeiss has subsequently introduced more stringent QC protocols.
Cheers,
David
I'm aware of diffraction limits etc and decreasing aperture decreasing theoretical resolution. So yes I should be referring to apparent sharpness rather than resolution. Maybe my SFs are a bit off (poor QC), but for sharpness and contrast the SFs don't get universal praise in comparison to other top bins. It sounds like the new ones with better QC may be better though. But for anyone else with 8x42 SFs who feel they would like the image to look a bit sharper, stopping down to 8x32 is worth a go - a lot cheaper than buying a new pair of binoculars.
David that's good to hear your another person who's tried this with their binoculars. It would be interesting to hear if anyone else tries it with the SF.
David that's good to hear your another person who's tried this with their binoculars. It would be interesting to hear if anyone else tries it with the SF.
Iirc, Henry Link has done similar things with his big 8x56 Zeiss glass.
He too noted improvement in sharpness. His experiences are posted on other threads here on BF, dealing with both sharpness as well as with CA. The topic has drawn considerable discussion and the conclusion was pretty clear, stopping down really helps when there is enough light.
I am guessing this will catch on and go far.
("Closing down opens up a new world!")
Now, do I rush in and get certain models and do this;
or wait till more people on this forum do it and report;
or wait till manufrs. provide these "ring caps", or
better, a camera-type diaphragm built in!
Mpeace, was there a reason for exactly 32 mm? Else
one might try other diameters to seek optimum results.
("Closing down opens up a new world!")
Now, do I rush in and get certain models and do this;
or wait till more people on this forum do it and report;
or wait till manufrs. provide these "ring caps", or
better, a camera-type diaphragm built in!
Mpeace, was there a reason for exactly 32 mm? Else
one might try other diameters to seek optimum results.
Last edited:
PeterPS I think it's the same as with photography where stopping down a lens brings a wider depth of field into focus. By cutting out the light from the edges of the objective that have to bend the most to achieve focus you keep just the central area which bends less and so the sharpness dosen't drop so quickly away from the focal plane. This means your eye's lens can then be more effective as well at making minor adjustments within a broader depth of field.
adhoc this is a zero expense way of playing around with binoculars, so best just to have a go with any pair you have. The reason for 32mm was simply that was the size of the bottle top I used to cut the holes. I was looking for something around that size to use and it just happened to be exactly 32mm. No need to wait for a product - it won't come, they want you to buy more binoculars. Just experiment with cardboard etc. You just need a sharp knife, some scissors, a bit of dark card/plastic and some masking tape or similar. My first effort took minutes try, worked a dream, but looked dreadful (see the pic). I wouldn't want to go out like that hence then making something a bit more aesthetically pleasing. I'm happy with the 32mm option, but people should definitely experiment with different apertures and optimise for their needs.
adhoc this is a zero expense way of playing around with binoculars, so best just to have a go with any pair you have. The reason for 32mm was simply that was the size of the bottle top I used to cut the holes. I was looking for something around that size to use and it just happened to be exactly 32mm. No need to wait for a product - it won't come, they want you to buy more binoculars. Just experiment with cardboard etc. You just need a sharp knife, some scissors, a bit of dark card/plastic and some masking tape or similar. My first effort took minutes try, worked a dream, but looked dreadful (see the pic). I wouldn't want to go out like that hence then making something a bit more aesthetically pleasing. I'm happy with the 32mm option, but people should definitely experiment with different apertures and optimise for their needs.
Attachments
Vespobuteo
Well-known member
"The depth of field which an observer can attain is primarily determined by the accomodation capacity of his eyes, then also by the magnification of the binocular, and to a lesser degree by the diameter of the effective exit pupil..."
From Holger Merlitz' book "Handferngläser", 1st edition 2013
Maybe it's the increased perceived sharpness that appears as more DOF?
But DOF per se, will not change with your modification. Not resolution either, rather the opposite, but I think you have realized that (post #4).
I would definitely send the bins to Zeiss for adjustment if you don't find them sharp in normal use.
There is always a risk in early samples that there are anomalies.
Last edited:
Thanks for the comments. I think the apparent sharpness/improved contrast may be the main reason and I am considering sending the binoculars in to Zeiss. I think I need to try them against a new pair. However, your quote from Holger Merlitz seems to support a change in DOF with aperture and therefore effective pupil size rather than saying it's a non-effect. The stopping down modification dosen't change my eyes or the magnification and so the lesser effect of the exit pupil diameter is all that remains and is still an effect. If I have a moment I'll try and digi-scope with the bins and see if that can show up what I think I'm seeing.
Thanks Mpeace for your response. I did not think 8x42 (say) with this feature will replace 8x32 in a model range: 32 will continue to appeal at lesser size and weight and lower price. If there is sufficient demand for this feature (spontaneously or induced by ads) a manufr. will only profit by providing it.
Yeh good points adhoc. My MK3 version of the objective aperture masks will be some rubber stay-on lens caps - very easy to switch between on and off depending on preference for more light or better definition. Would be so easy for a 3rd party manufacture to make these.....small market mind...possibly just me!
Vespobuteo
Well-known member
'Effective aperture' means the smallest aperture in the optical system.
So there will be no effect if your eye pupil is smaller than the exit pupil (4 mm). In daylight it will most likely be. But who knows, you might have extra large pupils?
I have discussed the DoF issue with Holger, and we are agreed the effective exit pupil will normally be the diameter of the pupil of the eye in brighter conditions. Having worn varifocal glasses for over ten years I have very little focal accommodation left. Providing the instrument EP is not limiting, I can assure you that the binocular objective size makes no difference to the observed DoF. However the effect of changing light level, and therefore pupil diameter, can be quite dramatic.
David
I have used stop down caps on many telescopes and some binoculars.
With cheap binoculars, the makers sometimes do it for you, with undersized prisms or vignetting internally.
Some 10x50s are actually 10x39.
Many binoculars are undersize and the marked specs. are wrong.
It is common for astro scopes to have small apertures in the front caps covered with another cap.
This is for solar observing with proper full precautions.
The heat with the full aperture may destroy a scope.
Plastic parts often melt.
With Newtonians a small offset front aperture gives a long focus unobstructed optical system.
Small cheap scopes, say 25mm aperture often have a 10mm stop behind the objective.
The objective is a single element, sometimes even plastic.
With cheap binoculars, the makers sometimes do it for you, with undersized prisms or vignetting internally.
Some 10x50s are actually 10x39.
Many binoculars are undersize and the marked specs. are wrong.
It is common for astro scopes to have small apertures in the front caps covered with another cap.
This is for solar observing with proper full precautions.
The heat with the full aperture may destroy a scope.
Plastic parts often melt.
With Newtonians a small offset front aperture gives a long focus unobstructed optical system.
Small cheap scopes, say 25mm aperture often have a 10mm stop behind the objective.
The objective is a single element, sometimes even plastic.
Vespobuteo - No, as far as I know I don't have extra large pupils.
Thanks David, Holger and Vespobuteo that's put me straight there. I think apparent increase in sharpness and contrast makes the image 'pop' more enhancing the 3D effect, but I'm convinced now there's no real change in DoF.
That's interesting Binastro. Why did you try stop down caps on your binoculars and did it have the desired effects?
Yes, it has the desired effect.
By reducing the aperture the focal ratio of the objectives changes from say f/4 to f/5.
A 42mm binocular might have objectives about 160mm focal length, f/3.8
By reducing to 32mm the focal length of the objectives is still 160mm, but f/5.
Also the eye is working nearer its optimum pupil size for resolution.
Many cheaper binoculars, say 20x60 or 8x56 are smaller than they state.
The top brands are usually correct, sometimes with minor variations.
I think that the Canon 10x42 L IS was originally 38mm but now nearer 42mm.
By reducing the aperture the focal ratio of the objectives changes from say f/4 to f/5.
A 42mm binocular might have objectives about 160mm focal length, f/3.8
By reducing to 32mm the focal length of the objectives is still 160mm, but f/5.
Also the eye is working nearer its optimum pupil size for resolution.
Many cheaper binoculars, say 20x60 or 8x56 are smaller than they state.
The top brands are usually correct, sometimes with minor variations.
I think that the Canon 10x42 L IS was originally 38mm but now nearer 42mm.
Very interesting.
So possibly the Canon was initially stopped down to achieve optimum sharpness, but then opened up in a misguided response to consumer pressure?
It could be, but I don't know Canon's reasons.
One reason the Foton 5x25 is so sharp, besides the very high quality optical figure, is that the objectives are a full 30mm aperture, but the binocular is stopped down giving a 5.0mm exit pupil.
Nowhere does it state 30mm.
Of course the 30mm objectives have a longer focal length than 25mm objectives, so they don't have to work so hard.
The Tewe 600mm f/5 lens I had was of near or actual astro quality. A Petzval design from memory, maybe 4 elements.
I also had two Astro Berlin lenses. A 600mm f/5 and a 600mm f/5.6.
These were identical lenses apart from one iris opening more than the other.
From memory simple doublets. The f/5.6 was of course better at full aperture than the f/5 at full aperture.
The multicoated 500mm f/5.6 Tele Tessar? for Pentacon Six looked beautiful, but had badly pinched optics. I suppose I could have remedied this but didn't.
In fact I think it was 500mm f/4.8 at full aperture with a huge front lens.
I can't remember which camera, maybe the Ilford Advocat? had different aperture lenses at different prices. But the lens was the same on both. Only the irises were different. This was cheaper than making two different lenses.
So playing around with f stops is common, but most folks are unaware of this.
I think that in the digital world the same sort of thing happens with sensors or other components. Reduce the price, by reducing the specs.
One reason the Foton 5x25 is so sharp, besides the very high quality optical figure, is that the objectives are a full 30mm aperture, but the binocular is stopped down giving a 5.0mm exit pupil.
Nowhere does it state 30mm.
Of course the 30mm objectives have a longer focal length than 25mm objectives, so they don't have to work so hard.
The Tewe 600mm f/5 lens I had was of near or actual astro quality. A Petzval design from memory, maybe 4 elements.
I also had two Astro Berlin lenses. A 600mm f/5 and a 600mm f/5.6.
These were identical lenses apart from one iris opening more than the other.
From memory simple doublets. The f/5.6 was of course better at full aperture than the f/5 at full aperture.
The multicoated 500mm f/5.6 Tele Tessar? for Pentacon Six looked beautiful, but had badly pinched optics. I suppose I could have remedied this but didn't.
In fact I think it was 500mm f/4.8 at full aperture with a huge front lens.
I can't remember which camera, maybe the Ilford Advocat? had different aperture lenses at different prices. But the lens was the same on both. Only the irises were different. This was cheaper than making two different lenses.
So playing around with f stops is common, but most folks are unaware of this.
I think that in the digital world the same sort of thing happens with sensors or other components. Reduce the price, by reducing the specs.
Entirely true, many computer chip versions start identical, with full capabilities, but are then binned into different categories by blowing fuses which shut off the excess features. I believe the same approach is used in software, download the whole package and unlock more or less of it depending on the license used.
Meanwhile, thank you for your insights on lens theory and practice. This bit of peripheral learning is one of the nice aspects of BF.
