Reciprocity at HIGH shutter speeds?

BetterSense · Dec 20, 2009

I have a reciprocity question.

Kodak datasheets sometimes say something like "for exposure times of between 1s and 1/10 000s, no reciprocity correction is required".

What happens above 1/10 000s? Does the speed of the film decrease like it does at low illuminances or does it increase?

removed-user-1 · Dec 20, 2009

BetterSense said:
I have a reciprocity question.

Kodak datasheets sometimes say something like "for exposure times of between 1s and 1/10 000s, no reciprocity correction is required".

What happens above 1/10 000s? Does the speed of the film decrease like it does at low illuminances or does it increase?

I believe that the same loss occurs at very high shutter speeds, since the basic problem is the low light level (due either to very low levels of ambient light OR due to a very short exposure). A film's data sheet should state the compensation for very high shutter speeds just as it does for low levels of ambient light. Tri-x, for example, requires 1/2 a stop more exposure and 15% more development at 1/10,000, according to the data sheet.

Pinholemaster · Dec 20, 2009

Sirius Glass · Dec 20, 2009

rthomas said:
I believe that the same loss occurs at very high shutter speeds, since the basic problem is the low light level (due either to very low levels of ambient light OR due to a very short exposure). A film's data sheet should state the compensation for very high shutter speeds just as it does for low levels of ambient light. Tri-x, for example, requires 1/2 a stop more exposure and 15% more development at 1/10,000, according to the data sheet.

When I worked a Kodak I talked to one of their top film chemists about this and why it was so. Basically he said at shutter speeds shorter than 1/10,000 second the short exposure caused reciprocity failures similar to the ones at long exposures for each film because the emulsion molecules were in a state of equilibrium at and shortly after the exposure and with very short exposures the electrons lost during exposure were recaptured by some molecules thus reversing the exposure.

Steve

msage · Dec 21, 2009

Sirius Glass said:
When I worked a Kodak I talked to one of their top film chemists about this and why it was so. Basically he said at shutter speeds shorter than 1/10,000 second the short exposure caused reciprocity failures similar to the ones at long exposures for each film because the emulsion molecules were in a state of equilibrium at and shortly after the exposure and with very short exposures the electrons lost during exposure were recaptured by some molecules thus reversing the exposure.

Steve

Yes, what Steve said!!?

Martin Aislabie · Dec 22, 2009

BetterSense said:
What happens above 1/10 000s? Does the speed of the film decrease like it does at low illuminances or does it increase?

Speeds decrease, but in the opposite way to low illumination levels.

At low levels of illumination it is the shadows that suffer

At high illumination it is the highlights that suffer first.

You can encounter exposures this brief if you use some small electronic flash guns at low power.

However, for most of us, its not a factor we usually worry about

Martin

Sirius Glass · Dec 22, 2009

Martin Aislabie said:
However, for most of us, its not a factor we usually worry about

Especially since my MF cameras are 1/500 second at the fastest and my 35mm cameras are 1/2000 at the fastest.

CBG · Dec 23, 2009

Martin Aislabie said:
Speeds decrease, but in the opposite way to low illumination levels. At low levels of illumination it is the shadows that suffer.
At high illumination it is the highlights that suffer first. ...

And as a further consequence of the reduction of speed in the highlights, at very short shutter speeds, contrast will tend to decrease.

This is the opposite of the effects of reciprocity failure from very long exposures where contrast increases.

Steve Smith · Dec 23, 2009

BetterSense said:
What happens above 1/10 000s

Do you have shutters that fast or is it just a theoretical question?

I suppose the same could be said of a fast burst of flash at a slower shutter speed with low ambient light.

EDIT:

Martin Aislabie said:
You can encounter exposures this brief if you use some small electronic flash guns at low power.

Great minds think alike (and fools never differ!).

Steve.

Lee L · Dec 23, 2009

Reciprocity failure in low light/long exposure situations is referred to as LIRF, or low intensity reciprocity failure. Reciprocity failure at short exposures is referred to as HIRF, or high intensity reciprocity failure. I believe that HIRF first became a practical issue with Edgerton's experiments with short duration electronic flash and strobe photography, especially with attempts to photographically freeze the motion of high speed objects like bullets.

Typical camera shutters and most uses of electronic flash don't get into HIRF territory.

Lee

CBG · Dec 26, 2009

Steve Smith said:
Do you have shutters that fast or is it just a theoretical question? ...

The most common occurrance of high intensity reciprocity failure involves small strobes and close range where a very brief exposure is enough.

fschifano · Dec 26, 2009

I don't think even small strobes at close distance get into this territory. However, I can think of at least one situation where it might become a problem - Plus-X wit a big studio strobe set to a very low power. For Plus-X it starts at 1/1000 second. The recommendation is to only increase development time by 10% for exposures this brief. at 1/10,000 second the recommendation is to allow an extra 1/2 stop and increase development time by 15%. It's all on page 2 of tech pub f4018. Just another reason you gotta love Kodak. The documentation is thoroughly comprehensive and accurate.

Reciprocity at HIGH shutter speeds?

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