My dear John! I think with a 50mm at 1:1 magnification the lens is approximately 100mm from the film/sensor and 100mm from the subject. I said approximately because I don't know where the nodal planes of the lens are.
I've done some!
I shoot quite a bit of slide film but I have no scanner, and while living in this digital, I had to come up with a solution to this problem myself.
Every time I go for a digitalization session this is what happens:
I have a canon T2i which I use to take the actual photos. Most of my lens and gear however is nikon so I bought a adapter ring to use my old AIS stuff on the digital.
I use a pk-13 tube extender and a 105mm/2.5 lens. A tripod and the 2sec delay to take the actual pictures (I have no cables or remotes for my digital). I make a lightbox out of a glass top table, a bedside lamp with a strong lightbulb, and some special heat tolerant diffusing paper to make and even light source. Custom WB is your friend here.
Yes, there are slight, but visible, distortions of all kinds when you look at the corners of the image. I can't attest to the fact that it's the sensors problem or the lens distortion with the tube extender (quite frankly, I don't care that much). Simple solution!! Don't fill the frame! I frame my duplicates to occupy the center of the image field and then I crop into the image later on. This way I leave the distorted areas out of my actual image. My camera spits out a 18MP image but after cropping my actual image size is generally around 6 or 7, which is more than enough to put on Facebook and emailing friends.
More quick tips that are quite simple:
Stop down the lens! I do most of the stuff at f/8
Don't raise the iso rating too much (200 gives good speed and little to no noise normally)
Don't let your exposures go on for ever. 1sec shots should do the trick normally. long exposures on digital can give rise to noise problems.
When scanning slides like this, I choose an exposure very simply. Make it so your light box (with no film over it) has just about overexposed (actually gone, I mean clipping). Like 1/3 of a stop too far and loss of information has started. Put a slide over it and adjust (you shouldn't be more than 2/3f away from ideal). Remember, adjust while looking at a histogram! Don't trust the light meter here, it wasn't made for this. Later on, pull blacks down just a little and you should be golden. Slides are A LOT easier than negatives for this stuff.
When scanning negatives things get little harder. Over exposing cases images to be quite dark and choosing a good exposure is quite tricky. Trial and error helps out more than anything.
Most important of all!!!!!!!!! Shoot these thing in RAW and adjust things accordingly later on.
And if this sounds convoluted and complicated for the simple task of scanning a picture. Well, it is(!!) and that's why I'm currently awaiting my scanner to come in. I got tired of doing this after a few months.
Best of luck
Ps: A special macro lens is probably best and an electronic flash would be interesting, but I would stay away from enlarger lens simply because.. Well this is already a ridiculous amount of work for a simple task, and my experience has been that a 250 dollar scanner will do an easier, faster(if you count the setup time), and better job. And though I think it might be feasible, I don't think you need more complications.
I however will admit dreaming of using a full frame sensor for a contact scan! Dreams will, for the time being, be dreams..
Last edited by Ambar; 07-12-2011 at 08:38 PM. Click to view previous post history.
Yes, if one needs it for a digital negative, and needs maximum quality over all the image surface, the enlarger lens, or a bellows lens, is a good move because the stuff is actually optimized for reproduction work (unlike normal lenses and even macro lenses).
If one only needs a copy for internet use (friends, email, facebook) then something like this is the best solution:
they call it "scanner" but it actually only takes a digital picture of the film. That means it is also very fast, you don't have to worry about exposure, and about setting a proper light source.
Can you say DOH! Of course it's 100mm! Smacks forehead. Again!
Heavily sedated for your protection.
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