Reciprocity failure rule of thumb

[Mark_3632]

I am looking for a rule of thumb that applies to reciprocity. I personally never noticed any reciprocity problems. I got good negs and chromes that always seemed to be properly exposed. Then again I do not know what to look for in the BW negs. I assume it is overall flatness or underexposure like it would happen on chromes.

I have done a lot of searching and cannot find a general rule of thumb for exposure and development?

Is there a film test to figure this out? I am getting efke, JandC Classic 200 and Bergger 200 for christmas so this is what I will use.

I've had a good track record so far and I would hate to start messing up now. Especially if it was something I could have avoided.

Mark

[Pete Caluori]

I don't think there is any blanket rule of thumb; certainly not for color. With B&W, Ilford's reciprocity for any exposure over 1 second is the exposure time in seconds raised to the power of 1.48 (Et^1.48). I guess that's about as close to a rule of thumb I've seen.

With color, not only will you have to adjust exposure time, but add color correcting (CC) filters as well. Each film will be different and the only way to know for sure is testing.

Regards, Pete

[jerry brodkey]

This is one of the reasons I use T-Max films. Just wish it came in larger sizes....

Jerry

[Tim Curry]

I've tried to find decent information about reciprocity with J&C 200 & Efke films (both of which I use almost exclusively now), no luck. For the most part, I've used the curve for Ilford's FP4+ which you can download from their web site (if you don't want to do the math in your head). I'm not sure how close it is as these films you've mentioned run the gamut from asa 25 to 200, but it seems to be fairly close from what I've done.

If you use Efke 25 in full light, try cutting the factor down some as it seems to be a bit on the long side with this slow film. Sorry, but I don't know how much, just that my exposures using the curve seem a bit overexposed in bright light. In low light it seems to be closer. You are correct in that your films will tend to be underexposed if you don't factor in some reciprocity for longer exposures.

[Kevin Crisp]

Mark: I have used the Kodak graph for Tri-X and had good luck with it. I reduce development about 15%.

See: http://www.kodak.com/global/en/professional/support/techPubs/f4017/f4017.jhtml?id=0.1.18.14.21.18.14&lc=en#Exposure%20and%20Development%20Adjustments%20for%20Long%20and%20Short%20Exposures

I've used that as a starting point with Ilford products and it has worked equally well for me. You might try it as a starting point for b&w products other than TMAX. Good luck.

[Alan Davenport]

Reciprocity Rule of Thumb: get the datasheet.

Films that appear similar often have very different reciprocity characteristics. There's no substitute for the right data.

[Philippe Gauthier]

I think that Alan is right. The reciprocity charcteristics of each film vary wildly and data sheets (easily available from the manufacturer) are your best starting point - probably the only starting point you need, actually. When I adopt or try a new film, I usually look at the data sheet to understand the film's merits and limits better. I keep a printed reference for the B&W films I regularly use. I urge you to do the same. It's cheap, easy and efficient. No more guessing!

[Christian Olivet]

Once you get the data, print a little table on an inkjet printer. It is better to use self sticking mailing labels. Go ahead an stick it on your light meter. I have it on my pentax meter. It works great!

[wm mitchell]

Email John at JandCPhoto. Sometime ago, he gave me some information about an unscientific "study" done on the Efke films from an German photographer that suggests that you can shoot Efke to 6 sec without adjustment; +1/3 stop to something like 15 sec; another 1/3 stop to 30 sec. Sorry my memory on this info is not that great, but I do remember that it supposedly rivals the reciprosity characteristics of TMax. Happy Holidays to all, BILL Wm. Mitchell

[Gene M]

You're better off sticking the label on a tripod leg, I think. (Christian's post)

[Brian Ellis]

If you use T Max 100 (and maybe 400 too, I don't use it so I don't know for sure) you don't encounter the need to make reciprocity adjustments until the exposure time reaches 4 seconds. With other black and white films the time is usually 1 second. I wouldn't get too obsessed with getting charts for each film you use, at least not black and white films. The reciprocity charts that John Sexton uses and hands out in his workshops just divides films into two categories, T Max and "All Others." I've been using these charts for years with both T Max and HP5+ and they've worked very well.

Don't forget that when you increase exposure times to compensate for reciprocity failure you also increase contrast so you have to reduce your development times(for black and white film that is, I don't know about color films I don't use them)unless you want the increased contrast in the negative. Any table that you use for reciprocity exposure adjustments should also give you the appropriate contrast increase at various extended times so that you'll know by how much your development times need to be reduced for each increased exposure time.