300mm Rodenstock Sironar-S vs. Sironar-N

[Ralph]

Forgive my ignorance, but I know nothing about lens design, 6 elements, 8 elements, plasmats, hazmats, and so on. My question is whether there is any sharpness difference between the Rodenstock Sironar-S vs. the "N." I am responsible for doing some super-high-resolution copywork of large illustrations (the glass on my old Caltar 300mm is beat to hell, but it's the right focal length). My shooting distance is about 7-10 feet (which I don't think moves it into the macro range). The client's goal is making huge Lightjet enlargements of the resulting 8x10 sheets scanned to digital.

I know the "S" has a larger image circle, but I don't need a lot of movement. The "N" would thus be a logical choice if the two series are equally sharp (there are two 300mm "Ns" -- I think -- on Ebay right now, although because the language in the two ads is almost identical despite sellers on different continents I'm suspicious of both, and one doesn't say "N"). But while searching the archives to see if this has been addressed, I saw Chris Jordan's post saying that he had found the answer to his sharpness quest in the Apo "S" series, so maybe there is a difference? And what about the "APO" designation? Are all Rodenstock Sironars going to be APO, or are there older "S" and "N" models that aren't? Should I care? (The illustrations to be copied are in color fwiw.)

For this current job, at least, "sharpness" is my biggest priority -- not weight, or filter size, or maximum aperture, or even cost (I'm not paying, just doing, and can sell the lens after the job is done if I don't think I'll use it again.) Any lens gurus able to comment?

[Bob Salomon]

The S is corrected for image ratios of 1:5 to infinity. The discontinued N is corrected for image ratios of 1:10 to infinity. For your type of work copying flat objects a 300mm Apo Ronar would be best. For table top studio work to infinity the S would be best.

[Ralph]

So the "N" is no more? OK.

By the way, I was going to add that I know the Schneider 305 G-Claron is highly-regarded. I didn't mention it only because a friend and I did multiple high-res tests of a Nikkor 360 vs. a G-Claron 355 and in every case the 355 was noticeably less sharp than the Nikkor, so I've always been wary about the words "G-Claron" when big enlargements are involved. But if the 305 version is likely to be sharper than anything else in the 300 class I'll consider that . . . or anything else likely to be "sharpest in class."

And if the consensus is that most modern lenses in this category are unlikely to differ much even under huge enlargement (I'm talking feet, not inches), I'll accept that too. (I've mostly done contact printing so I've never thought much about lens sharpness before.)

[David Karp]

A Caltar II-N from Calumet is the same as a Rodenstock Sironar-N. If you can find a used one, they typically cost less than the Rodenstock version of the same lens. They still show the 300mm f/5.6 on their website, but it is out of stock. Maybe it will never be re-stocked, unless Rodenstock is willing to do a production run for Calumet.

[Craig Wactor]

As I understand it, the "S" uses low-dispersion glass, which would give you more local contrast and therefore a sharper looking image. I do not think the resolution is actually higher, though. I also believe the S has 3 degrees more coverage than the N.

Both the Sironar-S and -N have been apochromatically corrected lenses all along. It was a marketing decision to add "APO" to the name. Both lenses have been updated through the years without changing the name, apparently. But I think any Sironar-S or -N is an APO lens.

I have used both the -N and -S version of the 150mm. They are both incredibly sharp, hard to tell the difference. My use has been mainly close to infinity, though.

If money is no issue, I would buy the Sironar-S, then ship it to me when you are finished with it ;o)

[paulr]

I just recently saw Schneider's own MTF charts for the 305 g-claron. It's just not a sharp lens. It's adequate for the 1:5 through 5:1 magnification it's designed for, but not much better than that. Terrible at infinity (at least compared to a modern plasmat). My guess is it's main design goal was affordability, unless there's something involved in process lenses that I just don't understand. The distortion numbers are nothing to get excited about either.

[Oren Grad]

Yes, the G-Claron MTF curves look OK until you read the fine print and realize that they represent 3/6/12 lp/mm, while the corresponding curves for the Apo-Symmar and Apo-Symmar-L represent 5/10/20 lp/mm.

[Ken Lee]

The tests performed here by Perez and Thalmann suggest that their sample 305 was as good, or better, than other lenses in the same category.



Do you consider this a fluke, or am I missing out on a little technical joke about lp/mm ?

[Oren Grad]

The tests performed here by Perez and Thalmann suggest that their sample 305 was as good, or better, than other lenses in the same category.

It's impossible to draw that conclusion based on a single poorly-controlled test at a single magnification that uses an inadequate performance metric. I don't think the Perez/Thalmann test results are useful, except to underline how hard it is to rigorously and quantitatively test optical performance in an amateur setup. At least on the basis of the information they provide, there's no way to disentangle the causes of the variation in results that they report for a given lens type, let alone use the data to compare different lenses in any meaningful way.

[J. P. Mose]

I asked this question a few months ago:

http://largeformatphotography.info/lfforum/topic/501320.html