Shooting LF lense wide open, what happens??greenspun.com : LUSENET : Large format photography : One Thread
I remember reading somewhere, never shoot LF lenses wide open.. however, I don't remember the reason why. Recently I was forced to shoot my Fuji 600C wide open.. which is f11.5...I needed the speed, I focussed on a subject at infinity, and the GG looked very sharp, I figured I would go for it... I was very disapointed at the results, the chromes showed showed very soft focus? I had changed the camera angle a few times, each time I refocussed, so I am sure it was not some silly error like bumping the camera or not having the focussing knob tightened all the way, etc.. Does anyone know what occurs when you shoot wide open with LF lenses?
-- Bill Glickman (firstname.lastname@example.org), December 13, 1999
You aren't getting the best definition wide open. depth of field from stopping down also gives you smaller circles of confusion. the smaller the circles, the sharper the image is. There is also the factor of where your film & holder actually is sitting in regard to the location of the groundglass.
-- Ellis Vener (email@example.com), December 14, 1999.
Ellis, I should have mentioned above, this roll film back performs flawlessly in the same camera when shot at smaller apertures. So I have eliminated that gg film alignment as the possible problem. The cc could be it, but I would not think it could be that drastic. I ruled out DOF, because I was shooting something that had a very tiny amount of required DOF, similar to shooting a wall. This may boil down to a lens test shooting targets at different apertures.
-- Bill Glickman (firstname.lastname@example.org), December 14, 1999.
Typically large-format lenses are designed so that the maximum aperture is for viewing only, not taking. The goal is to give you a brighter image to compose with. Unless you have ultra-fine ground glass, the image could still look pretty good on the ground glass but soft on the negative. For exposing the film, you might get good results one stop down from maximum, and should get good results two stops down from maximum. Taking photos near maximum aperture is where some of the new "apo" designs will beat older lens designs.
-- Michael Briggs (MichaelBriggs@earthlink.net), December 14, 1999.
Bill, That your images are sharp at smaller apertures might be a good reason why you DO have cause for concern about film plane/gg alignment. As you may recall from earlier threads, testing this relationship is done wide open to avoid the problem of depth of field masking the test results. The DOF of a 600mm is another consideration. Even a nearly flat subject, if close enough, could in part lie outside the range of sharp focus for that lens. Very few lens designs are intended for optimum performance at maximum aperture. An exception might be a lens like the Leitz Noctolux, which was specifically designed for wide open use in available darkness. Process lenses and better enlarging lenses also work well at larger apertures, but even then it's wise to close them one stop from max. Assuming your ground glass is fine grained enough, your results on film should look as sharp as it did in the gg, at least in one small area of your subject. There may well be other aspects of performance that do suffer wide open. Also, keep in mind that with the smaller format the range of tolerance for film plane/gg misalignment is somewhat smaller than it would be for 4x5 film. This, in order to assure acceptable results at larger magnifications. See my article in Nov./Dec. 1996 of ViewCamera and try the recommended test.
-- Robert A. Zeichner (email@example.com), December 14, 1999.
Photograph a yardstick at a 45 degree angle to the camera. This will give you an idea if it's a sharpness issue with the lens or a lack of agreement between your film holders and groundglass. The alternative of course is measuring all with a depth micrometer - the yardstick is quicker.
-- Wayne DeWitt (firstname.lastname@example.org), December 14, 1999.
Todays large format lenses are remarkably sharp centrally even wide open, abeit not at the same contrast level stopped down, so the lens would not be my first suspect. Try another lens to make sure. I concur with commentary. I suspect the GG position. It is easily to check. Shoot a wall (without any camera movements) at a tilted angle ( I find 15 degrees more revealing when you are wide open) that has a horizontal ruler taped to the wall. Focus mid way, between to two ends, on the ruler. Examination of the developed film to find where your actual focus falls. If there is aa error in focus then check the GG or your holders.
There are unusual instantances where ambient temperature differences between film and air causes the film to buckle during a long exposure. It has occurred a few times during during 5 to 30 minute exposures. If it happens you can tell it has by examining the film closely for double lines in the areas of poor sharpness.
-- Pat Raymore (email@example.com), December 14, 1999.
I don't know this particular Fuji lens, but I would expect good definition is possible with any modern lens, even wide open. I've mistakenly shot with a Rodenstock 210 wide open (we've all forgotten to stop down haven't we?) and the depth of field was quite shallow, but I did still have a plane of very good sharpness.
There are certainly errors possible like ground glass position vs. film holder position that will be even more aparent with the lens wide open.
-- mike rosenlof (firstname.lastname@example.org), December 16, 1999.
The best information on this subject can be gleaned at from studying the MTF response of the lens. I strongly suggest that you study this subject if you want to get the most factual information on lenses generally. Fortunately, MTF performance data is provided by Rodenstock and Schneider for LF optics and by Zeiss for all their optics. If you wich to learn about MTF, there are several sources including Schneideroptics.com and Zeiss web sites. Typically, the three german manufacturers that provide MTFs also provide other peerformance data such as distortion, illumination, and sometimes chromatic performance data. Unfortunately, among the Japanese manufacturers, only Canon provides some limited MTF data but only for their better lenses. It is important in looking at the MTF data to look for high contrast and tangential and radial curves that are as close together as possible. Depending on the design of the lens, its performance at maximum aperture can vary a great deal. The Apo Symmar 300mm and 360 for example deliver quite respectable performance at f5.6 and 6.8 respectively, i.e. full aperture, and improve closed down to f22. A large aperture in a long lens can provide highly selective focus. Look for example at the picture in the back cover of Sutterbug, January 2000 issue. It is a portrait taken with a Zeiss F2 110mm lens. The large opening allows very selective focus on the plane of the eyes, everything else is slightly out of focus. At this aperture this lens is not as contrasty nor as good generally as at smaller apertures (MTF), nonetheless the results, to me, are outstanding. Some lenses like the G-Claron perform well at small apertures but as their MTF indicates, their performance at infinity fully open will probably remind you of what you had with the Fuji C600. Since Fuji does not provide MTF data, and as yet photodo.com does not provide it for LF lenses, your only alternative is to experiment. Personally, I prefer to know what I am buying before I do, rather than to rely on hearsay or brand glory, -if I can avoid it. This means selecting optics for which their manufacturers offer performance data. I have not been disappointed when I did, but often disappointed when I did not. This is not to say that Fuji lenses are poor, quite to the contrary, many people think they are excellent. Quite obviously, manufacturers that offer performance data are not ashamed of their product. Hope this helps.
-- Julio Fernandez (email@example.com), December 28, 1999.