Image circlegreenspun.com : LUSENET : Large format photography : One Thread
I am looking to buy a 210mm lens with a 316mm image circles at f/22 (Rodenstock APO-Sironar-S 210mm f/5,6). I am new to 8x10 but not to large format, I use a 4x5. I understand that I need 325mm just to cover 8x10 and more to have movements. I also understand that at less than infinity focus and at larger f numbers the circle will get bigger. My question is: is it possibe to estimate the image circle from the above information at f/32 and f/45 at infinity?
-- jeff schraeder (firstname.lastname@example.org), January 16, 2002
Nope. It's all in the lens design.
-- Chad Jarvis (email@example.com), January 16, 2002.
As Chad says, some lenses are designed to give more coverage stopped down and some don't. I doubt the lens you mention will cover 8x10". For something in that focal length range with lots of room for movements in 8x10" you might consider a 10" Wide-Field Ektar.
-- David Goldfarb (firstname.lastname@example.org), January 16, 2002.
From personal experience I know that if I squeeze a 210mm G-Claron down to f32 it has an 82-84 degree angle of coverage. That's somewhere in the 340mm world. However I would caution that Schneider doesn't make any such claim for that lens. The probable reason is that since it was for copy use there is no mechanical vignette built into the design. So somewhere in that circle mtf does fall off to a point that would render things soft. My experience is that while I don't get a vignette in the corners, if there were important details in the extreme corners I might be in trouble. I would add that the fall-off isn't gradual. Things stay very sharp until the last 3/4 inch or so way out in the extremes. A lot of times that just means sky. These are trade-offs I'm willing to accept because of cost and weight consideratons. The 240mm G-Claron is great for 8X10. Lots of image circle to roam around in.
-- Jim Galli (email@example.com), January 16, 2002.
With the Rodenstock Apo Sironar S you get 3mm shift up and down and 2mm left and right thats almost nothing. If you find somewere a used Apo Sironar - W then you get a image circle of 352mm stated in the older brochure of Rodenstock. The other pos. is you take the next longer S version 240mm has already image circle of 372mm. Good luck!
-- Armin Seeholzer (firstname.lastname@example.org), January 16, 2002.
Jeff - The most probable answer is that there will be no increase with that lens's design. If you have an 8x10 camera you can experiment with lenses by looking for the aperture through the corner cutouts - if you can see the entire aperture (actually the light passing through it) it will place an image on the film. The suggestion to look for a Sironar-W is a good one - it can also include the Apo Sironar and Sinaron WS since these lens designations were precursors to the "Apo Sironar-W" and are of the same design.
-- Wayne Dewitt (email@example.com), January 16, 2002.
Armin, thanks for the info. I found Rodenstock's specs for the lens and it seems that at infinity at f/22 I can cover 8x10 but with the minimum movements you mentioned. That is my least likely scenario but I did want to at least have the capability. This lens will be used on my 4x5 in the field and on my 8x10 indoors. I can take the 8x10 out but will not do so very often and I would probably use a longer lens for landscape.
-- jeff schraeder (firstname.lastname@example.org), January 17, 2002.
The B&H Photo web site often has image circle specifications (at specific f stops) for large format lenses.
-- Michael Feldman (email@example.com), January 17, 2002.
Jejj- The lens you need is out there. As has been stated, it's the lens design more than the length that determines image circle. Go to www.graflex.org/lenses for a 14 page chart on lenses and there image circles. Good luck
-- Gary Meader (firstname.lastname@example.org), April 06, 2002.
Since I now own this lens and use it on 8x10, let me just add that the advertized image circle at f22, viz. 316mm, appears to me to be solid--my zeroed-out outdoor architectural shots show little significant degradation under a 4x loupe, although this is no substitute for a real test and enlargement would make a difference. You can look at the mtf curves and decide for yourself. Also, as you suggest, the image circle spec is for focus at infinity, so closer focus will help, but concern with diffraction makes stopping down any further unattractive to me personally. At 5x7, you'll get 73mm vertical, 61mm horizontal on horizontal format at f22 focused at infinity. Sometimes I let the image vignette at 8x10 (esp. skies) since I plan to enlarge someday and print elongated panoramas.
-- Nicholas F. Jones (email@example.com), April 07, 2002.