FrankS
Registered User
This topic came up recently in an unrelated thread.
http://www.rangefinderforum.com/forums/showthread.php?t=41941
Let's hash it out here.
The point that I want to make is that there is no reciprocity failure point, there is just a gradual variation from the normally linear response of film to changes in light. This is observable at (very high and) very low levels of light.
DMR's night photo was under exposed, but not due to reciprocity failure as was suggested, simply that the 1/30sec with wide open lens aperture used was not enough, with the development given, to obtain sufficient exposure.
http://www.rangefinderforum.com/forums/showthread.php?t=41941
Let's hash it out here.
The point that I want to make is that there is no reciprocity failure point, there is just a gradual variation from the normally linear response of film to changes in light. This is observable at (very high and) very low levels of light.
DMR's night photo was under exposed, but not due to reciprocity failure as was suggested, simply that the 1/30sec with wide open lens aperture used was not enough, with the development given, to obtain sufficient exposure.
V
varjag
Guest
Both Kodak and Fuji have reciprocity failure figures for their products at their respective websites.
I agree with FrankS conclusions. The *point* of reciprocity failure is listed for convenience, usually when deviation is no longer covered by camera shutter (im)precision or variations between emulsion batches.
I agree with FrankS conclusions. The *point* of reciprocity failure is listed for convenience, usually when deviation is no longer covered by camera shutter (im)precision or variations between emulsion batches.
ferider
Veteran
Another cool Avatar ... 
Anyway, here is all you need to know about it:
http://medfmt.8k.com/mf/reciprocity.html
Down to half sec it is in the same order of magnitude as lens
transmission loss of many lenses, or effective vs. labeled f-stop, and nobody
ever cares about those (see an article about about lens transmission
on Dante's website).
Roland.
Anyway, here is all you need to know about it:
http://medfmt.8k.com/mf/reciprocity.html
Down to half sec it is in the same order of magnitude as lens
transmission loss of many lenses, or effective vs. labeled f-stop, and nobody
ever cares about those (see an article about about lens transmission
on Dante's website).
Roland.
E
Edward Felcher
Guest
I'm against it. Call your government and sign petitions.
greyhoundman
Well-known
Peltier cooler on the pressure plate.
Xmas
Veteran
The film manufacturers data sheet normally has a graph. Some films are much more 'exposed' to failure.
Noel
Noel
Marc-A.
I Shoot Film
Ok I'm stupid but I need a lecture on reciprocity. Can someone explain me, with simple words, what reciprocity is about? All I believe to know is that at low speeds, colour films have different properties and you have to correct the exposure measured by the lightmeter. Is that it? Sorry, but I'm total ignorant on the subject.
K
Kin Lau
Guest
FrankS said:
I agree with the lack of a "point", but I'd just like to explore the "gradual variation" idea more. I've always taken it that past a certain level, the variation is quite pronounced. I know that people who shoot astro pics will stick with a slower emulsion since reciprocity failure for the faster films is quite drastic. Slow enough that a iso100 film at 5 min is more sensitive than a iso400 film at 5 min.
ferider
Veteran
Marc,
basically it means for long exposures (> 1 sec) at low light the film
sensitivity gradually decreases, so you need longer exposure times
than what is shown to you by the meter.
Also callled Schwartzschild effect, modeled with the Schwartzschild
coefficient. This coefficient is different for different films.
Roland.
basically it means for long exposures (> 1 sec) at low light the film
sensitivity gradually decreases, so you need longer exposure times
than what is shown to you by the meter.
Also callled Schwartzschild effect, modeled with the Schwartzschild
coefficient. This coefficient is different for different films.
Roland.
Xmas
Veteran
Marc-A. said:
You got it right
Low speed any film you have to use longer exposure time, colour film may need a colour shift filter to re-balance if the three layers have a different reciprocity failure rate, and you were picky about the colour.
High speed same effect.
Noel
Marc-A.
I Shoot Film
Thanks a lot, Roland and Noel!
Bryce
Well-known
I do a lot of long exposure shots of one kind or another, and have come to accept things as they seem to be, but here's something I think I've noticed that really bugs me-
If I open the shutter for say, 1/2 an hour and move around with a flashgun lighting up parts of the scene in front of the camera, invariably the film will seem less well exposed than I expected.
These images are in complete darkness save for the pulses from the flashgun, many dozens of them. So is that not the same as a long series of short exposures as far as the film can tell?
Is there such a thing as reciprocity failure for multiple flash exposures or am I dreaming?
I have used XP-2, FP-4 and HP-5 for these images and had the same experience with all of them.
Anyone know the answer?
If I open the shutter for say, 1/2 an hour and move around with a flashgun lighting up parts of the scene in front of the camera, invariably the film will seem less well exposed than I expected.
These images are in complete darkness save for the pulses from the flashgun, many dozens of them. So is that not the same as a long series of short exposures as far as the film can tell?
Is there such a thing as reciprocity failure for multiple flash exposures or am I dreaming?
I have used XP-2, FP-4 and HP-5 for these images and had the same experience with all of them.
Anyone know the answer?
FrankS
Registered User
From Wikipedia:
In photography, reciprocity refers to the relationship between different choices of aperture and shutter speed that result in identical exposure. Photochemicals exist for which the equation holds true in common cases. Outside of the normal range, the reciprocity law does not describe the actual behavior of light-sensitive material. This is known as reciprocity failure. At very low light levels, for example, the corresponding increase in duration required to produce an exposure can be higher than the formula states. That is, at 1/2 of the light required for a normal exposure, the duration may have to be more than doubled to expose the media. Multipliers used to correct for this effect are called reciprocity factors (see model below).
In most situations there is an inverse linear relationship between aperture and shutter speed, with a wider aperture requiring a faster shutter speed for the same exposure. For example, an exposure value of 10 may be achieved with an aperture of f/2.8 and a shutter speed of 1/125 s. The same exposure can also be achieved by doubling the aperture to f/2 and halving the shutter speed to 1/250 s; or by halving the aperture to f/4.0 and doubling the shutter speed to 1/60 s.
However, during very long exposures, film responds much more slowly than usual due to the fact that light is in fact composed of quanta known as photons, and film in turn is composed of discrete grains. The light sensitive grains within the film, crystals of a silver halide, must be hit by a certain number of photons within a certain timeframe in order for the light-driven reaction to occur and the latent image to form. In particular, if the surface of the silver halide crystal or film grain has approximately four or more ionised silver atoms, corresponding to an absorption of four or more photons, it is rendered developable.
This breakdown in the linear relationship between aperture and shutter speed is known as reciprocity failure. Each different film "emulsion" has a different response to long exposure. Some films are very susceptible to reciprocity failure, and others much less so.
In photography, reciprocity refers to the relationship between different choices of aperture and shutter speed that result in identical exposure. Photochemicals exist for which the equation holds true in common cases. Outside of the normal range, the reciprocity law does not describe the actual behavior of light-sensitive material. This is known as reciprocity failure. At very low light levels, for example, the corresponding increase in duration required to produce an exposure can be higher than the formula states. That is, at 1/2 of the light required for a normal exposure, the duration may have to be more than doubled to expose the media. Multipliers used to correct for this effect are called reciprocity factors (see model below).
In most situations there is an inverse linear relationship between aperture and shutter speed, with a wider aperture requiring a faster shutter speed for the same exposure. For example, an exposure value of 10 may be achieved with an aperture of f/2.8 and a shutter speed of 1/125 s. The same exposure can also be achieved by doubling the aperture to f/2 and halving the shutter speed to 1/250 s; or by halving the aperture to f/4.0 and doubling the shutter speed to 1/60 s.
However, during very long exposures, film responds much more slowly than usual due to the fact that light is in fact composed of quanta known as photons, and film in turn is composed of discrete grains. The light sensitive grains within the film, crystals of a silver halide, must be hit by a certain number of photons within a certain timeframe in order for the light-driven reaction to occur and the latent image to form. In particular, if the surface of the silver halide crystal or film grain has approximately four or more ionised silver atoms, corresponding to an absorption of four or more photons, it is rendered developable.
This breakdown in the linear relationship between aperture and shutter speed is known as reciprocity failure. Each different film "emulsion" has a different response to long exposure. Some films are very susceptible to reciprocity failure, and others much less so.
Tuna
Fotoğrafçı
Brian Sweeney said:
I prefer a solvent. A cream. I often slather A&D on the back of my camera and have had no issues.
FrankS
Registered User
At typical photographic light levels, there is no reciprocity failure. As light levels decrease (as with night time exposures), the degree of reciprocity failure increases and at some point must be taken into account.
Last edited:
Marc-A.
I Shoot Film
Thanks Frank for this detailed explanation. Always useful.
FrankS
Registered User
I started to write out the explanation, but then began to feel lazy and figured, why re-invent the wheel, and looked it up on Wikipedia.
Xmas
Veteran
If it is an auto flash or you are careful with the distance/guide number the flash should get you to day light levels, if that is what you wanted.
If you underexpose by sufficient 'zones' with the flash then it will still look dark.
Noel
If you underexpose by sufficient 'zones' with the flash then it will still look dark.
Noel
Bryce
Well-known
Noel-
I use a manual flashgun (Vivitar 285, set to manual) and establish the number of pulses with an incident flash meter.
I have the problem acceptably under control, I just tell the meter I am exposing 50 speed film when I use XP-2 and usually get workable negatives.
As I said, I have yeat to find a reference to the phenomenon, and that after lots and lots of searching around. The photos (see my gallery, it's the 'Underground' series) are done in a way similar to cave photography, but I get a little more creative about lighting from various angles than most. The common consensus among the cave shooters is to use enormous, Meggaflash flashbulbs to light an area underground, but the method is a little too stark for my purposes. I like to look at the lack of natural light as an opportunity for studio lighting methods.
Anyway, this is just something that has been puzzling me for a long time. I should probably run some more scientific tests- like same image, but with one pulse wide open, two at one stop closed down, etc. and compare the negs.
Reading about Neopan Acros having virtually no reciprocity failure has made me want to try it for this technique, and I will, it just hasn't happened yet.
I use a manual flashgun (Vivitar 285, set to manual) and establish the number of pulses with an incident flash meter.
I have the problem acceptably under control, I just tell the meter I am exposing 50 speed film when I use XP-2 and usually get workable negatives.
As I said, I have yeat to find a reference to the phenomenon, and that after lots and lots of searching around. The photos (see my gallery, it's the 'Underground' series) are done in a way similar to cave photography, but I get a little more creative about lighting from various angles than most. The common consensus among the cave shooters is to use enormous, Meggaflash flashbulbs to light an area underground, but the method is a little too stark for my purposes. I like to look at the lack of natural light as an opportunity for studio lighting methods.
Anyway, this is just something that has been puzzling me for a long time. I should probably run some more scientific tests- like same image, but with one pulse wide open, two at one stop closed down, etc. and compare the negs.
Reading about Neopan Acros having virtually no reciprocity failure has made me want to try it for this technique, and I will, it just hasn't happened yet.
Xmas
Veteran
If you use the 285's guide number and a single flash on a grey card near coaxial with the lens line of sight then you should get a grey card like it was daylight.
Do you set the flash meter at the object, and step back, flash and take a reading, and then multiple shoot?
Noel
Do you set the flash meter at the object, and step back, flash and take a reading, and then multiple shoot?
Noel