Resolution measurement 8x56 SLC (1 Viewer)

[Tringa45]

I have tried several times in the past to measure the resolution of my binoculars using an Edmund Optics USAF 1951 glass slide and a 3x12 Zeiss tripler but failed, firstly because of the diificulty in affixing the tripler behind the binoculars' ocular and secondly because my old eyes require more than the modest 3x boost.
Henry Link has suggested using a second binocular as a booster, so today I set up my 8x33 Kowa Genesis on a second tripod behind the Swarovski 8x56 SLC.
The USAF glass slide was illuminated from the rear by a white translucent bedside lamp and I was intermittently able to see the vertical and horizontal lines of group 3, element 4 in both barrels.
This is a line spacing of 11,3 line pairs/mm and at the viewing distance (objective to slide) of 6,27 m translates to a resolution of 2,9 arcseconds.
The objectives of hand-held binoculars usually have fast focal ratios and one would not expect them to get close to the Dawes' limit, which for a 56 mm objective would be 2,07".
In this context I think 2,9" is an excellent result for the SLC.

John

 

[Maljunulo]

That is a very interesting number, and somewhat better than I would have expected for a binocular.

 

[[email protected]]

I have tried several times in the past to measure the resolution of my binoculars using an Edmund Optics USAF 1951 glass slide and a 3x12 Zeiss tripler but failed, firstly because of the diificulty in affixing the tripler behind the binoculars' ocular and secondly because my old eyes require more than the modest 3x boost.
Henry Link has suggested using a second binocular as a booster, so today I set up my 8x33 Kowa Genesis on a second tripod behind the Swarovski 8x56 SLC.
The USAF glass slide was illuminated from the rear by a white translucent bedside lamp and I was intermittently able to see the vertical and horizontal lines of group 3, element 4 in both barrels.
This is a line spacing of 11,3 line pairs/mm and at the viewing distance (objective to slide) of 6,27 m translates to a resolution of 2,9 arcseconds.
The objectives of hand-held binoculars usually have fast focal ratios and one would not expect them to get close to the Dawes' limit, which for a 56 mm objective would be 2,07".
In this context I think 2,9" is an excellent result for the SLC.

John

Resolution of all equal quality binoculars at 8x are going to be the same regardless of aperture size because, you really are never going to see any difference. It doesn't do any good to use a booster because when you use the binocular you are using your own eyes, not a boosted image. If you think one binocular is sharper than another, you're fooling yourself.

 

[Tringa45]

That is a very interesting number, and somewhat better than I would have expected for a binocular.

Yes, a very reassuring result even if it vastly exceeds my visual capabilities.
Perhaps the objective design profits from the more exacting requirements of a 15x binocular in the same line-up.

John

 

[Tringa45]

Resolution of all equal quality binoculars at 8x are going to be the same regardless of aperture size because, you really are never going to see any difference. It doesn't do any good to use a booster because when you use the binocular you are using your own eyes, not a boosted image. If you think one binocular is sharper than another, you're fooling yourself.

Perhaps you should have qualified that as "perceived" resolution, but I'm with you there.
And then these "assessments" are often hand-held on lower contrast targets.

John

 

[tenex]

Resolution of all equal quality binoculars at 8x are going to be the same regardless of aperture size because, you really are never going to see any difference. It doesn't do any good to use a booster because when you use the binocular you are using your own eyes, not a boosted image. If you think one binocular is sharper than another, you're fooling yourself.

That is of course false; differences in sharpness are sometimes easily seen (and a common reason for individual preference) and may even be due to the lower aberrations of a stopped-down larger aperture. What you presumably mean to have said is that aperture (i.e. Dawes limit) is not the limiting factor in binocular resolution as it is in higher magnification (and quality) telescopes... but no one had suggested that it was.

 

[[email protected]]

Yes, a very reassuring result even if it vastly exceeds my visual capabilities.
Perhaps the objective design profits from the more exacting requirements of a 15x binocular in the same line-up.

John

Exactly. Boosted resolution measurements are meaningless at the magnification levels binoculars are designed for.

 

[[email protected]]

That is of course false; differences in sharpness are sometimes easily seen (and a common reason for individual preference) and may even be due to the lower aberrations of a stopped-down larger aperture. What you presumably mean to have said is that aperture (i.e. Dawes limit) is not the limiting factor in binocular resolution as it is in higher magnification (and quality) telescopes... but no one had suggested that it was.

I said binoculars of equal quality. Surely a $100 MIC binocular is not going to be as sharp as an alpha but when comparing a Zeiss SF 8x32 to a Swarovski NL 8x42 both are going to have the same apparent resolution to the human eye. Aperture has nothing to do with resolution at 8x because your eye will never see any differences. I was once asked Zeiss if aperture had any bearing on resolution, meaning would an 8x42 SF binocular be sharper than an 8x32 SF binocular, and this was their answer.

Dear Dennis,

Thank you for contacting ZEISS Consumer Products.

Both instruments would be equally sharp for what they are, but the 42 mm objective, as you stated, would allow for a bit more light.
The 8 power would simply give you a bit more field of view, but they are both equally sharp.

Please visit COP Community to get answers to many of your questions.

Best Regards,
Everett Sherman
Zeiss Consumer Technical Support
Zeiss Sports Optics

ref:_00D20MWc0._5006M2ECKuz:ref

 

[henry link]

Dennis, How can you know two binoculars are of equal quality if you don't test them to their limits and not just to the limit of your particular eyesight acuity?

I guess I'll have to pull out this old post again.

Victory HT 8x42

Hello, Visiting my son at London, after been with him at his PhD in Economics graduation in the EUI (European University Institute), Firenze, Italy, I made a visit at Harrods. Just to take a look at the place. As the last year, they have DEALS in binoculars. Two were VERY GOOD SALE offers...

www.birdforum.net

In this case the aperture of the 8x56 binocular has been stopped down to match the aperture of the 8x30, but because of its lower aberrations there is still an obvious difference in the true resolving power between the two, even though both can resolve line pairs well beyond anyone's eyesight acuity. Also notice the difference in the appearance of "sharpness" of the largest line pairs, which are easily resolved by both binoculars but look sharper in the stopped down 8x56 than in the 8x30. This is where eyesight acuity may cause one person to see both binoculars as equally sharp, but another person with higher acuity will notice that the one with lower aberrations looks sharper.

 

[[email protected]]

Dennis, How can you know two binoculars are of equal quality if you don't test them to their limits and not just to the limit of your particular eyesight acuity?

I guess I'll have to pull out this old post again.

Victory HT 8x42

Hello, Visiting my son at London, after been with him at his PhD in Economics graduation in the EUI (European University Institute), Firenze, Italy, I made a visit at Harrods. Just to take a look at the place. As the last year, they have DEALS in binoculars. Two were VERY GOOD SALE offers...

www.birdforum.net

In this case the aperture of the 8x56 binocular has been stopped down to match the aperture of the 8x30, but because of its lower aberrations there is still an obvious difference in the true resolving power between the two, even though both can resolve line pairs well beyond anyone's eyesight acuity. Also notice the difference in the appearance of "sharpness" of the largest line pairs, which are easily resolved by both binoculars but look sharper in the stopped down 8x56 than in the 8x30. This is where eyesight acuity may cause one person to see both binoculars as equally sharp, but another person with higher acuity will notice that the one with lower aberrations looks sharper.

That doesn't prove anything. You are still using a greatly boosted image to see the differences in resolution. My point is with normal eyesight at 8x, you are not going to see any differences in resolution between a Zeiss SF 8x32 and a Swarovski NL 8x32, as Zeiss says above. All these aberrations you point out are done with boosted images that you are never going to see at the magnification levels binoculars are used at. Binoculars have all kinds of aberrations in them that you can see if you greatly increase the magnification, but it is meaningless at the 8x to 10x powers they are normally used at, and the manufacturers know this, so they don't worry about it, and we shouldn't either. Sure, if you put a 600 mm FL telescope behind the binocular eyepiece with the camera sensor at prime focus you are going to see a difference in resolution and increased aberrations, but how many people do that when they are using the binocular birding? Let's get real, Henry!

 

[henry link]

You don't seem to have noticed that those images demonstrate that the aberrations that degrade the measured resolution of line pairs well beyond anyone's eyesight acuity can also reduce the image quality (sharpness and contrast) of much larger line pairs that are readily visible at normal binocular magnification. Compare the sharpness and contrast of the line pairs 0-2 to 0-6 in the images. They're large enough to be resolved at 8x by most people and easily resolved by both binoculars, but not equally sharp.

 

[Tringa45]

You don't seem to have noticed that those images demonstrate that the aberrations that degrade the measured resolution of line pairs well beyond anyone's eyesight acuity can also reduce the image quality (sharpness and contrast) of much larger line pairs that are readily visible at normal binocular magnification. Compare the sharpness and contrast of the line pairs 0-2 to 0-6 in the images. They're large enough to be resolved at 8x by most people and easily resolved by both binoculars, but not equally sharp.

Could we conclude then, that low longitudinal CA is the dominating factor in perceived central sharpness and contrast rather than SA?

John

 

[henry link]

Hi John,

The Habicht also has higher SA, more clearly revealed by a star-test. Hard to say which one contributes more to the image degradation.

Henry