Testing coverage of lenses

[xkaes]

Perhaps you're thinking of Fujinon A lenses: they are optimized for 1:5.

Slight correction. The A lenses are optimized for 1:1 to 1:5, but I've used my A 180mm f9 from 2X to infinity with results satisfactory to me.

[Ken Lee]

Excellent - Thank you !

[Pere Casals]

Sironar S lenses are optimized for 1:10.

Sironar N lenses are optimized for 1:20.

Perhaps you're thinking of Fujinon A lenses: they are optimized for 1:5.

Thanks for pointing it.

So for a 1:20 magnification (Sironar-N210mm) we need little some 4.5m distance from lens to the target. It would be interesting to see how many Lp/mm are lost as focus is closer.

[Pere Casals]

Sironar S lenses are optimized for 1:10. See http://www.arca-swiss-magasin.com/co...-sironar-s.pdf

Sironar N lenses are optimized for 1:20. See http://www.linos.com/pages/mediabase...r-n_e_2474.pdf

Perhaps you're thinking of Fujinon A lenses: they are optimized for 1:5.

One contradictory thing is that Sironar-S graph looks worse than the Sironar-N:



Sironar-S Modulation for 20 Lp/mm falls earlier (as off-axis distance grows) than Sironar-N . I guess this is because scale is not the same, 0.05 vs 0.1, so Sironar-S test is made in more a complicated situation for a lens that is also optimized for distant objects.

[Bob Salomon]

One contradictory thing is that Sironar-S graph looks worse than the Sironar-N:



Sironar-S Modulation for 20 Lp/mm falls earlier (as off-axis distance grows) than Sironar-N . I guess this is because scale is not the same, 0.05 vs 0.1, so Sironar-S test is made in more a complicated situation for a lens that is also optimized for distant objects.

The curves on the N chart start their drop at 78.7mm of coverage, the S chart starts the drop 10 mm further out.

All of the first three S curves start above 90% they are higher then the N curves.

You have to realize that the bottom scale is for half of the coverage of the lens design so the S scale is expanded further out then the N scale since the S covers a larger circle.

[Pere Casals]

The curves on the N chart start their drop at 78.7mm of coverage, the S chart starts the drop 10 mm further out.

All of the first three S curves start above 90% they are higher then the N curves.

You have to realize that the bottom scale is for half of the coverage of the lens design so the S scale is expanded further out then the N scale since the S covers a larger circle.

Thanks for pointing it Bob, I had not seen that the abscissa had a different scale, related to a larger circle.

Anyway the 45 corners (153.7 mm Diagonal/ 2, so some 75mm is farthest point) are better for the N, 70% vs 60% modulation transfer for 20Lp/mm, if 45 sheet is well centered in the circle.

I ask myself what graph would it have the S at 0.1 scale...


What it is also true is that if the 45 film is not well centered in the image circle then with N corners go earlier to much lower performance.


Anyway I guess that S may have some ED elements (isn't it ?, I think I read that somewhere), and this is what may make the real difference, as secondary chromatic aberration may be lower, at the cost of larger thermal expansion of the glass, and probably more curved surfaces design because lower refraction index, so slightly more weight.


I guess that real practical difference S vs N is not well explained by the (20Lp/mm) graphs. Also those graphs don't speak about ultimate resolved Lp/mm(+70?), where secondary chromatic aberration may have a real effect on resolved lines amount, and microcontrast.

[Jac@stafford.net]

The problem here is that the ground glass itself loses illumination from center to corner and needs to be subtracted out in the calculations.

No. If you wish to measure corner illumination, please consider aerial focus throughout the the entire field.

But two points: Why are you asking a large format group about your testing of miniature formats? Scale does not follow ordinary arithmetic, and including enlarging lenses is irrelevant regardless of film size because it is an entirely separate empirical paradigm.

[xkaes]

No. If you wish to measure corner illumination, please consider aerial focus throughout the the entire field.

But two points: Why are you asking a large format group about your testing of miniature formats? Scale does not follow ordinary arithmetic, and including enlarging lenses is irrelevant regardless of film size because it is an entirely separate empirical paradigm.

Three points back at you:

#1. The instrument I have is designed to measure light on the ground glass, not aerial measurements. The original OP wanted to know how "we" measure things, so I offered my approach. You don't like it? The OP doesn't like it? Fine with me. No one is forcing anything on you.

#2. I am in no way asking anyone to compare smaller formats to larger formats for the purpose of this discussion. I am merely showing how I set up my tests. The original OP wanted to know how "we" measure things, so I offered my approach. You don't like it? The OP doesn't like it? Fine with me. No one is forcing anything on you.

#3. I may be in the minority, but I actually make prints. So I always include results of my -- lens, film, developer, etc. -- tests made through an, appropriate for the format, enlarging lens (which has also been tested for optimum results). But that's just how I do it. You don't like it? The OP doesn't like it? Fine with me. No one is forcing anything on you.