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Thread: DIY digital camera stand / or scanner w BW film... D-range to low for bit depth?

  1. #1

    Join Date
    Oct 2007

    DIY digital camera stand / or scanner w BW film... D-range to low for bit depth?

    So I set up a very crude digital camera stand to quickly convert a few negs to digital. I used a very nice Sinar multishot MFD back at iso 25. The resolution was good and the D range was greater then the film but now that is what is troubling me. If I leave the camera to linear output then the image is such a small part of the 14bit histogram that it is noticeable combed after I expand it. I can change the endpoints in capture shop in post but I do not know if that actually will improve image quality as the problem seems to be in the raw data and I dont think there is a way to set the camera to lower the dynamic range so the bit depth is finer within the range of the film.

    Now that I think about it I really could do more to mask the image, which would increase contrast some.

    Still, I'm working with black and white film (Fp4). Doesnt that have a dmax of around 1.8 or 2? A Dmax of two is 100 times darker then a dmax of which is somewhere between 6-7 stops of contrast) If my camera capture 12 stops then a lot of data is lost. I could see DIY scanners working extremely well for slide film which captures the world in less stops and shows it in great contrast. Actual a film density range of 3.6 has a contrast ratio of 4000:1 and 12 stops is 4096:1 so a 12 stop camera would be an ideal to digitize chrome film (with just a little room to prevent clipping).

    Are you guys getting good results with your DIY cameras and negative film? It has 1/40th the contrast ratio of negatives. I know high end CCD and drum scanners allow the analog signals to be adjusted prior to going through the analog to digital converter which makes them more ideal for film digitization. Can this be done with regular or MFD cameras as well?

  2. #2
    Peter De Smidt's Avatar
    Join Date
    Jan 2001
    Fond du Lac, WI, USA

    Re: DIY digital camera stand / or scanner w BW film... D-range to low for bit depth?

    This is an important issue. Unfortunately, I don't know which scanners allow pre-digital conversion signal optimization and which do not. Film for a diffusion enlarger often only goes to about 1.3 above film base plus fog. Film developed for a condenser system typically has an even lower max density. While it's true that less development will lead to smaller grain, it can lead to a lower density range which can lead to poor tonality when scanned. I ran into this recently when I scanned an Tech Pan negative from many years ago. The photo was a studio nude, and TPs contrast can be hard to get a handle on. The negative had a low density range. I scanned it with my Cezanne. Unfortunately, giving the image the contrast I wanted with Photoshop led to posterization. I'll try re-scanning again, aiming to produce a file closer to my final vision right out of the scanner, but I'm not sure it'll help. Does ColorGenius adjustments, such as setting white and black points, lead to a better optimized analogue signal before A/D conversion? I don't know. If the resulting file has better tonality, then the answer is probably "yes", but I'm doubtful that this will be the result.

    With a dslr camera "scanner", we can adjust the light source, for instance is color and intensity, as well as change shutter speed and apertures. This allows us to get a good exposure. But for negatives with a limited density range, that may not be enough for good tonal quality. One option is to increase the negative density range through intensification, or through making a mask. I'd like to avoid that if possible. Another option would be to take multiple frames, changing the exposures. There should suffice. With one exposure, look to place your highlights close to what you want in the final negative. With another place your mid-tones, and finally place your shadows. Now blend the frames together using special software or use luminosity masks to manually do it. The resulting file should need much less tonal manipulation to get to your final image, and that should minimize tonal problems.

    Another options would be to use an led monitor as the light source, using an image of the film from a prior scan to add to the new scans density range.

    Now that I have a studio, I'm going to do some tests comparing low density range negatives and negatives developed and exposed to make more use of the scanner's sampling system. That won't happen any time soon, alas.
    "Why can't we all just get along?" President Dale, Mars Attacks

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