Schneider says that their Digitar lenses provide superior resolutation that digital backs need. Superior to what? I have looked on their web site and compaired their 90mm Digitar lens to their 90mm Super Angulon. One is measured at 4.5 and the other 5.6. I split my screen so that I could look at the charts side by side, and I really can't see the Digitar advantage. I am not however an expert on optics. Some other web sites that I have looked at make it sound like if I don't run right out and buy digitally optomized lenses, I might as well shoot with broken pop bottle bottoms. I would be very interested in what you guys think.

Neal

-- Neal Shields (shields@ftw.com), December 28, 2001

Answers

Neal:

From what I have gathered corresponding with Schneider and Rodenstock reps is that the real advantage of these digital lenses is slightly better performance at higher spatial frequencies (40-60 lp/mm) at larger apertures (f/8-f/11), in exchange for smaller image circles. So at f/22, they're all diffraction limited, but for shooting at f/8, the digital lenses will deliver slightly better performance. Whether this is observable on roll film is a subject of controversy... some say yes, others say probably not, since film flatness and other variables will likely be greater than the performance difference.

-- Glenn Kroeger (gkroeger@trinity.edu), December 28, 2001.

I have a friend who has a Hassy with the 150mm lens and I have a Kowa with the 150mm lens, we photographed the same subject with the same film and printed our negs on the same enlarger with the same lens and there was no visible difference, forget the advertizing, check the prints. Pat

-- pat krentz (patwandakrentz@aol.com), December 29, 2001.

Neal, I'm curious....what camera/back are you intending to use these lenses with?

-- Robert A. Zeichner (info@razeichner.com), December 29, 2001.

No, I am not in the market for a new lens. It is not a new lens that my photography needs, it is a new photographer. I have even taken a plastic lens out of a cheep Polaroid, mounted it to my Linhof, and shot with that. Even then, my photography doesn’t seem to suffer. So I expect it will be a while before I grow out of my Angulons etc.

However, while waiting for some talent to miraculously appear, I occupy myself trying to understand the craft side of the equation.

Everything I have read about “digital” lenses says that they are better for both digital and film. Comparing the graphs on Schnider’s web site, (which I thought I was beginning to understand), the data doesn’t seem to support this.

The only thing that I can see that could improve a lens for digital would be moving the nodal points as in a reverse telephoto in order to change the angle of the light ray hitting the pixel, however, I would expect that to result in a disadvantage for use in film photography.

-- Neal Shields (shields@ftw.com), December 29, 2001.

"Everything I have read about “digital” lenses says that they are better for both digital and film. Comparing the graphs on Schnider’s web site, (which I thought I was beginning to understand), the data doesn’t seem to support this. "

Then you may find that Rodestock's detailed brochure with illustrations of the differences will make it clear for you.

But it will have to be mailed.

It was written and illustrated by Dr. Walter Schoen

-- Bob Salomon (bob@hpmarketingcorp.com), December 29, 2001.

Neal,

image circle size and resolution are two contradictory goals in lens design. The past development (and market need) of large format lenses has mainly lead to larger image circles and less increase of resolution. The smaller digital sensors will not need large image circles any more. Large Format is currently downsized to a sole "View Camera" with a stress on DOF and perspective control - don't even considdering a Ground Glass.

Since the pixels on these modern digital sensors are more tightly packed than most film grain, they require higher lens resolution. Due to the Sampling Theorem, the regular arrangement of these pixels do require even more lens resolution compared to the random spread film grain.

So these "Digital Lenses" simply have other design goals. If you are shooting Roll Film than you might be happy with digital lenses, too. If you prefer Sheet Film, forget about them.

Regards,

-- Thilo Schmid (tschmid@2pix.de), December 29, 2001.

Neal:

I am curious what graphs you are comparing, since most "normal" view camera data sheets don't give information for spatial frequencies higher than 20 lp/mm. It is the 40-60 lp/mm range that "digital" lenses are designed to optimize.

Glenn

-- Glenn Kroeger (gkroeger@trinity.edu), December 29, 2001.

http://www.schneideroptics.com/photography/large_format_lenses/super- angulon/56_90/mtf2.html

http://www.schneideroptics.com/photography/digital_photography/90/page 5.php

I am compairing the MTF graphs on these two pages. From looking at them, even adjusting for the one stop difference it would seem that the Angulon is better? I have always read that MTF was a better measure of resolution than LPM because one required a subjective judgement by the viewer and the other could be done objectively.

Sinse they are both Schneider measurements, one would assume that there are no other measurement variables that would give one an advantage over the other.

Neal

-- Neal Shields (shields@ftw.com), December 29, 2001.

Neal,

as Glenn pointed out, you have to look at the right curves. In The MTF-Graph of the Super-Angulon, the line belonging to 20lp/mm is the lowest and in the Digitar it is the top most line. The Super-Angulon Chart do not show lines for 40 lp/mm and 60 lp/mm. And if you compare the two lines for 20 lp/mm you can easily see that the Digitar has better resolution, especially when looking at dotted line of the tangential frequencies.

Regards,

-- Thilo Schmid (tschmid@2pix.de), December 30, 2001.

Thilo you're right. I assumed that they were using the same scales. Now I have to wonder if this is a major breakthrough in lens design. Why weren't lenses like these offered before? I thought lenses and optics were the limiting factor in photographic detail not the film??? Usually in design you don't get something for nothing. This seems to be something, I can't help but wonder what the down side is.

Neal

-- Neal Shields (Shields@ftw.com), December 30, 2001.

Neal:

The "nothing" is something, it is reduced coverage and smaller image circles... not a problem with the smaller area of digital sensors... previously, virtually all large format lenses had been designed to cover at least 4x5"

-- Glenn Kroeger (gkroeger@trinity.edu), December 30, 2001.

You're right Glenn, sometimes I am just slow on the uptake. I was compairing a lens with a 100mm IC to one with a 200mm IC.

-- Neal Shields (shields@ftw.com), December 30, 2001.

Neal et all: Using 120mm lenses Digitar and Apo Symmar for comparison, it is quite obvious by studying the 20 lpm MTFs (f11 for Digitar, f22 for ApoSymmar) that the Digitar's performance is relative to its magnification and increases from 1:1 to 1:4 i.e. closeup photography, while that of the ApoSymmar is more constant throughout a magnification range. Schneider does not provide an MTF at 1:4 for the ApoSymmar but it gives one for 1:5. The Digitar at 1:4, at centre shows slightly greater higher contrast than the ApoSymmar at 1:5, but then you are comparing a specialized closeup lens with a multiple purpose lens. What would happen if both could be compared at infinity? The data provided by Schneider for the Digitar only applies to closeup photography and that is a sure indication of the real design purpose of the lens. If you are a landscape photographer there is no gold in those there digital hills!

-- Julio Fernandez (gluemax@sympatico.ca), January 06, 2002.

Julio:

While I agree that the Digitar's appear optimized for 1:5, Shneider does have MTF curves for 1:50 on their site... thats infinity enough for me.

-- Glenn C. Kroeger (gkroeger@trinity.edu), January 06, 2002.

Trying to reproduce Julio's results, I find the the Digitar slightly better at infinity and f/11. I used the following data:

Digitar 120mm: http://www.schneideroptics.com/photography/digital_photography/120/pag e5.php

Apo Symmar 120mm: http://www.schneideroptics.com/photography/large_format_lenses/apo- symmar/pdf/apo-symmar_56_120.pdf

At f/11, infinity (1:50 for the Digitar which is optical infinity) and 20 lp/mm, radial response:

Center: Digitar 82% (Radial and Tangential) Apo-Symmar: 75% (Radial and Tangential)

45mm off-axis: Digitar (60% of image circle radius): 78% (Rad and Tan) Apo-Symmar (50% of image circle radius): 70% (Rad and Tan)

60mm off-axis: Digitar (80% of image circle radius): 75% (Rad and Tan) Apo-Symmar (66.67% of image circle radius): 72% Rad, 55% Tan

While these numbers would not likely produce any observable differences at 20 lp/mm in on-film performance, it is certainly NOT the case that the Digitar is worse at infinity, despite its optimization parameters,

Interestingly, the Digitar seems to have an edge in coverage at f/11 since the Apo-Symmar drops off precititously beyond 70mm off axis. And of course, we don't have data for the Apo-Symmar at 40 and 60 lp/mm, but could suspect that the Digitar would be somewhat better since that is what it was designed for. At f/22, the Digitar and Apo- Symmar will both be controlled primarily by diffraction rules.

-- Glenn C. Kroeger (gkroeger@trinity.edu), January 06, 2002.