Reciprocity error

[Hlop]

Hi guys!

I'd like to try night shooting on film which I've never done before but I've heard about reciprocity error on long exposures. Could you, please, tell me about it in few words and/or suggest something good to read about it?

[greencardigan]

The short version:

Breakdown in the linear relationship between aperture and shutter speed is known as reciprocity failure.

The full version:
http://en.wikipedia.org/wiki/Reciprocity_failure

I did a bit of reading up on this when I was all excited about pinhole cameras.

[gstark]

Mikhail,

Good question.

Under normal circumstances there's a fixed relationship between the factors that vary the exposure on an image that you're going to make. For instance, 1/125 @ f8 is the same as 1/60 @ f/11 or 1/250 @ f5.6. Each of these values will yield the same amont of light for the creation of your image.

When you bring film into the equation, and start using longer or shoter exposure times, this relationship begins to break down, and where you might normally expect the same relationships to apply (1 second @ 5.6 = 2 seconds @ f 8 = 4 seconds @ f 11) what actually occurs is that the image on the film, at, say, that four second exposure, might appear to be underexposed, and in order to yield a correctly exposed image, you may need to compensate by increasing the exposure to perhaps six or eight seconds.


Here's a couple of references to this that I found after a quick google.

http://www.nyip.com/tips/tip_reciprocity698.html

http://medfmt.8k.com/mf/reciprocity.html

Hopefully others will be able to add more to this.

[Hlop]

Thanks a lot!

Just wondering if this sort of error affects digital as well or film only? For example, if I'm using D70 to take a picture with long exposure, can I apply same exposure settings to a film camera or should I correct exposure in accordance to reciprocity error?

[gstark]

Mikhail,

Reciprocity applies to each type of film differently, and most films should have factors publicly available for this, for each type of film. Thus FP4 will be different from HP4 will be different from K25 will be diffferent from E64 and so on.

It therefore follows that this doesn't apply to digital photography.

[Matt. K]

Mikhail
For night shooting add one stop to metered exposure....works every time! Or, if possible, bracket. (Not fun on a medium format camera). Or...check internet for film type exact reciprocity tables. PS Correct term is reciprocity failure.

[Hlop]

Thanks people!

Matt, I still have FED-2, so I can waste few meters of cheap 35mm film playing with bracketing

Another funny film toy is coming soon but I'll keep it in secret for a while