Infinity

[Huw Evans]

But, Pete, it is true! Actually I don't think we're likely to be in genuine disagreement here, because I know that you know the optical formulae as well as I do, but I think we're talking about it from slightly different perspectives. You are comparing images made with fixed magnification on film, and I am comparing images made with fixed lens to subject distance.

If I photograph, let's say, a postage stamp at 1:1 with a 50mm lens on a 35mm camera, then I need an extra 50mm of extension from the infinity position, and two stops compensation. If I photograph the same stamp at 1:1 with a 400mm lens on an 8x10, then I need a total of 800mm extension and, again, two stops compensation - as you say. However, as we all know, the latter set-up produces a radically different picture, with the stamp lost in a sea of empty 8x10 negative.

My earlier comments were from the point of view of producing an equivalent framing - say a portrait taken with a lens of equivalent angle of view, and from a similar distance. In this case the magnification ratio for the 35mm and 8x10 frames is radically different, and hence the discrepancy. For a given subject distance the longer focal length lens is extended proportionately much further than the shorter one.

[Jim Galli]

Bernard, are you confused enough to pitch out the bellows camera yet, or whould we keep going? I like the f8 f11 answer the best. Jim

[Bernard Negrin]

I think I got it now! Thanks for all of your responses. You have all been quite helpful. Until my next question...Regards, Bernard

[Pete Andrews]

Ahh! I see what you mean now, Huw. If you want to cover the same subject area, then yes, you have to extend the LF lens relatively more. You also have to be that little bit further away from the subject. A 1 metre lens to subject distance using a 50mm lens on a 35mm camera needs about 1.2 metres using a 5x4 with 210mm lens to get the same area in shot.