Expert: John Oliverio - 10/21/2003

Question
Hello John,
I know that film emulsions (at least B&W) contain grains of light-sensitive compounds and, if I remember correctly, the grain size varies with the speed of the film. My question is can the number of grains per inch on film be compared to the number of pixels per inch on a digital image? How many ppi would a digital camera have to have to give the same resolution as, say, 35 mm ASA 400 film? Does a 5 megapixel camera give an image that has greater resolution than the film? Thanks for your help.
Gary

Answer
Gary,

Hello. Thanks for the questions.

Unfortunately there is no clear answer.  And I firmly believe that trying to compare the two is futile.

Grain is not an analog to pixels.  Grain is an analog of signal noise.  Besides, there is no standard or ISO to the number of grains a given ISO has.  That is actually one of the major areas of competition among film makers:  to make less grainy high-speed films.

There are too many factors to say something like "5mp is equal to 35mm film".  Not all 5mp chips are created equally!  I believe every statement made on the subject must be heavily qualified.  For example, I personally believe that 5 or 6 mp can (not IS, as it depends on the maker) be equal to film, but only if the chip is in a dSLR.  Not a p/s camera.  I've seen great results, as good as and in some ways better than film from the Canon 10D and Nikon D100.  My wife and I have a 10D, and I'm so happy with it that I'm now ready to sell my film cameras and buy a second digital body.  However, I do recoginze the limitations.  For example, I don't expect to be able to make 30x40 inch prints from the 10D.  I can with film, if I shoot slow slide film.  However, in all the years I've been shooting film, I've only done that twice!  So I just don't care.

This is all very subjective.  I suggest that you ask yourself what you want of a digital camera, that find if there is one than will do it.  If you need help with that aspect of it, let me know.

John