Mark Parsons, all: This is getting off-topic, so this will be my last post on the list about this subject. Regarding the debate about medium format lenses and 35mm bodies... Mark argued that medium format lenses by definition must have the same or better resolution than 35mm lenses, or else photographs made with them would be less sharp; results show that they are sharper. This is not true. Why? 1) Medium-format images use larger negatives. This results in less enlargement to get the same print size as 35mm film. As a result, film grain plays a much lesser role in image quality. I think you would all agree that shots on a really good quality, low-grain film are sharper than shots on a faster, high-grain film. (I know some people think that images shot on, say, Tri-X seem sharper than images on slower films, but examine the image under magnification. The sharpness of grain can give the illusion of image sharpness, but if you examine the image carefully, you will notice that the image sharpness [e.g. really fine detail] is not as good.) 2) Medium-format images, because of the lesser enlargement, do not require the same degree of lens sharpness as 35mm lenses because the images are magnified less. Let us assume that Joe uses his Nikon FM2 and 50/1.8 AI-S to shoot an image. Let us assume that his brother Bob uses his Pentax 67 with 80mm f/2.8 image to shoot the same image. (Perspective with each lens on its native film format is roughly the same.) Each makes an 11x14" print from his negative. Joe's 35mm negative is 2.4x3.6cm or 8.64 square centimetres; Bob's is 6x7 cm or 42 square centimetres. Notice that Bob's negative is almost 5x (4.86) larger than Bob's. I realize that cropping will play a role because the 35mm negative does not enlarge perfectly to 11x14", but let us assume that the image is printed in a format that prints the entire negative onto the identical print area. In reality, the 35mm print would be slightly cropped and enlarged even more than this example, making my point even more dramatic. So ... to make that 11x14" print, which in metric is 27.94x35.56 cm or 993.54 square centimetres, requires: - 35mm negative - 115 x enlargement - 6x7 negative - 23.65 x enlargement This results in a 4.86 x difference, just like before. So ... even if a 35mm lens had double the resolution of the 6x7 lens (I am assuming resolution would be proportional to the square of the magnification; if my assumption is wrong, then this could be 4x resolution difference and not 2 and still be true), the 6x7 image would still be somewhat sharper JUST BASED ON THE LENS QUALITY ALONE, and totally ignoring the fact that the image is sharper because of improved film quality due to lesser degrees of enlargement. Don't believe me? Try a test and see. Just remember that if you use 35mm film and 120 film, and use the same emulsion, the 120 film is going to have higher resolution right off the mark (due to lesser enlargement) unless you compare a similar area of film. If you use the same focal length of lens on both cameras (exact focal length - e.g. 85mm on the 6x7 and 85mm on the 35), and examine the same, small piece of detail from each negative, you will be overriding the film differences and you will see that the 35mm image is sharper. If you want the logical, instead of mathematical, argument, think of this: what's easier to make, a small lens covering only a small image circle, or a larger one covering a large image circle. The larger you make a lens, the larger the pieces of glass become and the harder it is to make them effectively and accurately. (This is also part of the reason why you have 80mm f/2.8 normal lenses on medium format cameras, and 50mm f/1.8 or f/1.4 normal lenses on 35mm - it would be extremely difficult to design a quality lens with an f/1.4 aperture for a medium format camera. Of course, it would also cost $2 million :) ... but that cost is because of the design difficulties. A 50/1.8 lens for a 35mm camera, new, can cost under $100 US and be an extremely sharp optic.) Hopefully somebody here has an archive of Popular Photography issues and can find that article written a few months ago that discusses this issue, and then you will all believe me. Jim _________________________________________________________ DO YOU YAHOO!? Get your free @yahoo.com address at http://mail.yahoo.com
