Differences between 150mm Apo Sironar S and N

[Marco Gilardetti]

Your suspicion is unfounded. The magnifications specified are consistent with Rodenstock's design parameters, namely, the N series at 1:20 and S series at 1:10.

So, in simple words (correct me if I'm wrong), one can't simply put the MTF graphs of the S and the N side by side and compare, correct? Actually, just by looking at the curves and ignoring the 1:20 1:10 thing, the N would seem to be slightly better than the S, which I don't think it may really be as it is described in the foreword as a "good option on a budget".

So, how does the performance of the two lenses (and the two MTF set of curves) compare? Does the 1:20 vs 1:10 thing mean that the S is almost on another planet, or just slightly better than the N?

[Bob Salomon]

So, in simple words (correct me if I'm wrong), one can't simply put the MTF graphs of the S and the N side by side and compare, correct? Actually, just by looking at the curves and ignoring the 1:20 1:10 thing, the N would seem to be slightly better than the S, which I don't think it may really be as it is described in the foreword as a "good option on a budget".

So, how does the performance of the two lenses (and the two MTF set of curves) compare? Does the 1:20 vs 1:10 thing mean that the S is almost on another planet, or just slightly better than the N?

Are you comparing the total curve or just the curves for the same coverage? Since the S covers a larger circle then the N.

[Ken Lee]

If you search this forum, you'll see that Bob has tirelessly addressed this question (in its many variations) for years.

His patience is to be admired.

[Marco Gilardetti]

I trust his patience on your word, but if someone has to explain with great patience the same thing over and over again, this is usually not because people is stupid but because there is something which is made very confusing and very counter-intuitive in the matter. The same lens brand that uses the same lens name and shows their respective performance on two graphs that looks the same with the same dimensions on page BUT have a hidden rescale (or whatever it is) on one of their axis is what I call something more or less intentionally done to confuse people. So no surprise that a lot of people is confused.

I tried to read the mentioned lot of past posts concerning this matter but I can't even figure how this matter is named, I'm afraid. I tried a search with the keywords "MTF ratio" but came up with nothing, at least reading the threads' titles.

Yes, I'm comparing what seems to be the same line at what seems to be the same point at what seems to be the same aperture for the same focal length. Or, at least, that's what numbers seem to say.



At an image circle of seemingly 51mm, the N seems to score 70% while the S seems to score less than 60%. In MTF graphs usually a 60% performance is considered worse than a 70% performance, or at least this is what I've always believed. The more you're close to 100%, the better it is.

Same things happens - more or less - at 30mm.

So if it wasn't for the above discussion, I would straightly deduce that the S is sensibly worse than the N. Gently, where's the mistake?

[Taija71A]

... I tried to read the mentioned lot of past posts concerning this matter but I can't even figure how this matter is named, I'm afraid. I tried a search with the keywords "MTF ratio" but came up with nothing, at least reading the threads' titles.

Marco, nobody ever said that this particular 'topic' would be easy to understand.
BTW... MTF stands for “Modulation Transfer Function”.

How to Read MTF Charts.
https://photographylife.com/how-to-read-mtf-charts

How to Read MTF Curves.
http://www.zeiss.com/content/dam/Pho...ial_mtf_01.pdf

Regards, -Tim.

[Oren Grad]

So, in simple words (correct me if I'm wrong), one can't simply put the MTF graphs of the S and the N side by side and compare, correct?

Correct.

[Harley Goldman]

I owned the 150 S for a while. Great lens. But I shot 4x5 images side by side with the S and a Nikkor 150 and with an 8x loupe, I could not see any noticeable difference in sharpness. So I sold the S and pocketed the cash. As always, YMMV.

[Bruce Watson]

I'm thinking the same design considerations must apply to the 150mm Apo Sironars, making the N version a better choice for landscape and the S version a better choice for close-up work.

I don't know why you think that. I've got a pristine copy of the 150 Sironar S, and it's hard to image what you could possibly think is going to be sharper about the N. The damn thing makes my fingers bleed when I touch it. Will the N do that? IDK and IDC.

What I think is that yer barking up a tree that doesn't contain a squirrel.

Working with a view camera in the field is different than working with a lens on a lens bench. Once you have a lens that's "sharp enough" the limit on sharpness ceases to be the lens, and becomes about everything else, and that includes you and in particular, your technique. We use view cameras largely for the movements, and the movements themselves and their adjustments, can take the edge off the sharpest lens. And this is a good thing (as you'll figure out if you make enough photographs) because there's way more to a good photograph than simple sharpness. Way more.

This quest for the sharpest lens is related to the endless arguments on this forum about diffraction.

"That way madness lies." -- Shakespeare, King Lear, Act 3, Scene 4

[Dan Fromm]

Correct.

Why not? The coverage difference leaps out of the two charts posted. The -N's contrast at f/5.6 and 20 lp/mm goes to 0 at ~ 90 mm off-axis, the -S's at approximately 114 mm off-axis. At f/22 and 20 lp/mm the -S is farther ahead of the -N at ~ 90 mm off-axis. If you're going to shoot 4x5 without movements the two lenses are about equal, otherwise you should want the -S.

[Oren Grad]

Why not? The coverage difference leaps out of the two charts posted. The -N's contrast at f/5.6 and 20 lp/mm goes to 0 at ~ 90 mm off-axis, the -S's at approximately 114 mm off-axis. At f/22 and 20 lp/mm the -S is farther ahead of the -N at ~ 90 mm off-axis. If you're going to shoot 4x5 without movements the two lenses are about equal, otherwise you should want the -S.

Remember that the two charts are showing MTF at different magnifications. They are not directly comparable because the curves will shift with changes in magnification. In particular, the N will gain coverage at 0.1x relative to what is shown in the existing curve at 0.05x - or, conversely, the S wlll lose coverage as you move it out to 0.05x from 0.1x. There may also be changes in the shape of the modulation curve beyond a simple stretching with magnification, because of the effects of different mixes of corrections chosen to optimize the two designs for different magnifications. In such well-behaved designs these changes are likely to be incremental over this magnification range, but if one's point in looking at MTF's to begin with is to split hairs between two excellent lenses, extrapolation is arguably invalid. We also know nothing about sample variation from these charts.

If one must have the absolute best performance for a given application, there is no substitute for obtaining the lenses that are under consideration and conducting comparative tests in the required use. Yes, this can be costly and inconvenient.

PS: FWIW, I own both N- and S-series lenses. I happily use both types, but the S lenses do have more usable coverage and the way they render focus transitions is just a bit more refined. I learned this latter attribute from using them - it's not anything I could read off of the MTF's.