danlsmith wrote:
The table shows a reduction of sensitivity for longer exposures, not for shorter ones. So, films exposed at 1/4000 thru 1/8000 are not affected by it. 15 to 30 seconds or longer, yes. P.S. the table does not make reference to digital, only film.
That is simply not true. From an old film shooter. There is no data because nearly no one had a shutter faster than 1/1000 s. But there info from Kodak about extraordinary short exposures. Flash film exposures can have it but it is apparently built in to the guide numbers. And varies by film type. But from the period I had exposure charts that showed non-linear light response of Reciprocity failure at both ends. Here is a reference:
CAMERA: Exposure and Light How to Overcome the Reciprocity Failure
By ANDY GRUNDBERG
Published: February 5, 1989
HAVE you ever taken pictures just after sunset and found later that they come out underexposed with an unattractive shade of green? Have you ever had some of your flash pictures come out darker than they should? If so, you may have been a victim of what's known as reciprocity failure.
What's reciprocity failure? Let's backtrack to some basics of exposure. We all know (or we should) that the amount of light reaching the film and the film's density after development have a mutual relationship. That is, if we open the lens a stop, the on-film exposure should double. The same goes if we use the next slower shutter speed. Double the exposure, double the density. This one-to-one, reciprocal relationship is the basis on which exposure measurement is built. But at the extreme ends of the speed spectrum, the relationship breaks down. Instead of 30 seconds giving twice the on-film exposure as 15 seconds, it may produce only a third more density. This is reciprocity failure.
Every film reacts differently to short and long exposure times. But in general, here is what happens:
With long exposure times (usually a second or longer), the film slows down, producing underexposure. Color film also changes colors in weird and unsightly ways, producing overall color casts.
With short exposure times (faster than 1/1,000 sec.), the film also loses sensitivity and underexposes. Color shifts are involved, too, although they usually aren't as noticeable as in long exposures.
So who shoots pictures at speeds shorter than a thousandth of a second? You do, if you own an automatic flash that quenches its output based on exposure feedback. Automatic flashes of this sort can cut off in as little time as 1/100,000 second - short enough to cause reciprocity failure in most films.
If you shoot color-negative film, you probably haven't noticed any of these so-called reciprocity effects. That's because color negatives have a built-in cushion, tolerating underexposures of a stop and sometimes more. Since most reciprocity effects are within this cushion, you don't see the underexpose in your prints. And unless you have a sharp eye, you won't see any color shifts, since the printing process tends to mask them.
Slides are another matter. Being sensitive to exposure variations of even a third of a stop, they show the effects of reciprocity readily.
To avoid reciprocity failure's unwanted effects, you need to consult the film manufacturer's recommendations. When data sheets came as separate pieces of paper inside every box of film, this was a piece of cake. But nowadays reciprocity information is included only with so-called professional films - especially the ones that come in sheet-film sizes.
Today we have to search for the information. My aged copy of ''Kodak Color Films,'' Kodak's Publication E-77, has a chart listing both short and long exposure corrections for its various color films. Although out of date, it shows that
most films act as we want them to between speeds of 1/1000 and 1 second. The exceptions are pro films designed for long exposures (sometimes called Type L) and the Kodachromes, which don't need any short-exposure correction even at 1/10,000 sec.
My copy of Modern Photography's Photo Information Almanac, published yearly, reproduces the latest Kodak chart and adds one for Fuji films. The only fly in the ointment is that both manufacturers keep upgrading their emulsions, so these charts get out of date fairly rapidly.
What if you're stuck in Afganistan on a moonlit evening and you don't have your reference library with you? As a rule of thumb, most slide films need about a half stop more exposure at one second times, one to one and a half more stops at 10 seconds, and at least two more stops at a minute or more. Since these shutter speeds are likely to be outside the range of your meter anyway, I'd advise bracketing.
And remember: always make your exposure compensations by opening the lens aperture. If you change the time the shutter is open, you'll also change the reciprocity effect!
On the short end of the scale, try increasing flash exposures by half a stop to a stop when you're focusing closer than four feet. The nearer you are to your subject, the shorter the auto-flash exposure will be, and the greater the reciprocity effect.In terms of color shifts, the possibilities are endless. Kodak films can go anywhere from too yellow to too red. If you are shooting under street lights at night, these shifts may not make be a problem; the colors are going to be strange anyway. If you want accurate colors, experiment with a roll. As long as you stay with the same film, its results will be consistent, and predictable.