Does anyone use a computer for sensitometry? : LUSENET : B&W Photo - Film & Processing : One Thread

Since my darkroom has to double as a computer study, I thought I'd make more use of the computer for printing and processing. My half thought out idea (half-baked perhaps) was to plot the characteristic curves of the films and paper that I use into a spreadsheet; such that I could get a readout of subject brightness versus expected paper density for various development times and paper grades. I reckon the few minutes spent on the computer would at least put me in the right ball park before I even fire up the enlarger. Any thoughts? Anyone else tried a similar system?

-- Pete Andrews (, July 20, 2000


No reason you can't do this, but it may use (waste?) more time than it saves. I got some nice programs from X-Rite that let me load density readings directly from the densitometer into the computer via the RS232 port. It was fun to play with, but developing a usable system was more than I wanted to contend with. I continue to spot check negs, but print 99.9% by eyeball and gut feel. A commercial lab might be able to justify this better than a sporadic hobbiest (me!).

-- Conrad Hoffman (, July 20, 2000.

Greetings Pete,

I put a computer in the darkroom for that purpose. I'm still in the process of of getting it set up the way I want, but I'm using it to track negatives and prints, exposure info, density readings etc. Done properly, you should be able to extract useful information. The one word of caution is the afterglow of the CRT's phosphur can fog film and paper.


-- Pete Caluori (, July 20, 2000.

I've made characteristic curves of film and found it enjoyable to prove to myself that the curves shown in the books are indeed the way film and developer behave.

Now I use densitometry to select film speed (I use 0.1 above fb+f, which is a standard definition of B&W film speed I believe) and developing time (I aim for D=1.15 for Zone VIII which works well for my condenser enlarger).

Print making is, as Conrad said, by eyeball. I don't think you would find yourself refering to your database very often. I'll bet you'll still fine-tune your prints once you see your first print of a particular negative.

-- Don Karon (, July 21, 2000.

I use a computer for characteristic curves of film (very useful) and paper (hardly useful at all). I have a database of the images, which helps me to find pictures fairly quickly, and I keep notes of how I make prints, so I can easily make more prints.

I suppose a densitometer on the negative (or meter on the enlarger baseboard) could give you basic exposure and contrast information, but with experience you should be able to get that in a single print, and that print will then give you information about required local variations in density or contrast.

-- Alan Gibson (, July 21, 2000.

Cheers guys. From your replies, it looks as if I'll have to re-think this. My first thought was a to use the spreadsheet as a guide to paper grade and exposure, but it might be more useful as an indication of the development to give a specific film/subject combination. I guess I'll just have to give it a go, and see how it works out. Thank you all.

-- Pete Andrews (, July 24, 2000.

Pete, although I don't use one myself, I'm pretty certain a sensi based system could be made to be extremely effective. However, to develop it for just yourself is probably nowhere near cost effective. I doubt a spreadsheet based program would be useful enough.

Do you already own the densitometer? If not, I would point out one real problem; most machines will not allow you to read into really small areas. Something like a 3mm (transmission) diameter reading spot is typical. I know that Macbeth units can typically be fitted with either 1 or 2mm diameter apertures; even so, this may not be small enough for a typical 35mm film user. The black mask around the reading aperture makes it hard to accurately position your neg.

Although I said that I don't personally use such a system, I've had a lot of experience in these general areas; feel free to email with more specific questions if you'd like. IMO, you are exactly on track on the part about translating subject brightness into paper density.

-- Bill C (, July 24, 2000.

I use my Handspring Visor, works great for note-taking and calculating, plus the backlight on it does not emit (barely) IR and the visible light is so weak i have to set the visor down (face down) on the sheet of RC III i'm using to fog it...

great, I am now off topic...


-- Jason Tuck (, September 12, 2000.

What you are looking for has been developed by Phil Davis and sold through, Fred Newman. Software is amazingly sophisticated and reliable, adaptable to zone system, etc. Integrates readings on paper with negatives. Complex, but once the choices are made the negatives and prints are boringly reliable. If you check out Davis' book from the library "Beyond the Zone System," you will find the formulas and theory that indicate why doing this in a spreadsheet is a lot more trouble than it is worth. One problem: to date, the software only runs on Mac, but you don't need to use it much once you get your curves and data run. Find a friend.

-- D. Meriwether (, May 31, 2001.

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