Film Speed VS Usage & Reciprocity

Hi guys and thanks much for your having indulged my seemingly (to me anyway) endless questions and meandering forays into photographic knowledge (& discovery thereof).

 

SO here's another question, although I confess Im not sure what exactly I am asking.

 

But here we go:

 

Having done some reading on shooting under various conditions, And having learned only a tiny bit here & there about some things related to photography, I THINK I get that reciprocity refers to the "exposure triangle" , IE; how aperture, ISO, & shutter speeds can vary in a sort of circle to achieve basically the same effect under varying conditions, camera ability, etc... IOW say my 500CM camera, for example has limited settings for well pretty much everything (or more so, the lenses do?) So I can't get high speeds, and the aperture ranges from f2.8 to f16.

 

Based on that, I so far with whatever result, have either metered then adjusted up or down to attain an exposure that works for the camera, tried to meter with my digital camera set to whatever ISO I was shooting at the time, or consulted my "sunny 16 rule" chart which covers anything from ISO 100 & up in pretty much all sorts of daylight conditions- and done the same.

 

SO while I am (maybe) not so completely lost as to why this works the way it does, I believe I understand the basic notion of reciprocity... ?

I'm asking :-)

 

Meanwhile, I have done a fair amount of shooting with assorted 400 speed films. Although at some point I shot a couple rolls of some old Portra 160. Mostly, when the results are good, they're pretty good. Although at some point some of the portra 160 stuff came out grainy (at least he scans & proof prints seemed grainy to me. I also shot some Ilford HP2, I think it was? A C41 process B&W film and some of those shots also seemed a bit grainy. As stated, I adjusted up or down the scale of reciprocity to attain something I could get to, using the available settings on my 500CM with the 80mm lens... Trying, of course, to keep it in the neighborhood for prevailing conditions (daylight, overcast, bright, no shadows, etc)

 

I haven't put the negs on a light table or anything but having seen the scans and proof prints... is there any reason to believe the negatives would reveal anything different than what I've seen already?

 

why would some films be grainy? Outdated, old, or expired, maybe?

 

Also... are there limitations as to what say, a 160 ISO film should be able to do? VS a 400 ISO film? In theory, are lower ISO films supposed to be finer than those of higher ISO values? And if so, should I use a lower ISO film for, say trying to shoot brightly lit things at night? With smaller apertures and longer exposure times?

 

Does reciprocity cancel out conditional anomalies, and allow most things under most conditions?

 

Thanks again!

Tom

OK so I asked a photographer friend about reciprocity and he said it's basically adding exposure time to low light photography using different ISO films...

to quote: "Reciprocity is a formula for adding time to really long exposures. Film handles long exposures differently so usually need to add time to shutter at a certain point..."

 

By that I assume he means exposure values for ISO 400 (or higher) would be different than ISO 100 or ISO 50 (or lower), and that every film is different so each would require its own settings in a low light situation.... ?

Rather than me trying to explain reciprocity, read this: Reciprocity (photography) - Wikipedia

Reciprocity – More correctly “reciprocity failure” explained: In photography we have a law called the Law of Reciprocity. Exposure = Intensity X time. The light falling on film (or digital sensor) accumulates all the time the shutter is open. Say an exposure setting is 1/60 of a second @ f/11. We can also expose this vista using 1/30 of a second @ f/16 or 1/15 of a second @ f/22 or 1/125 of a second at f/8. All these exposures and many other combinations not listed will yield the same level of exposure and this is what we mean by the Law of Reciprocity (equal work for equal pay).

 

 

Now this law begins to fail when the exposure time greatly lengthened. We are talking exposure times greater than 1 second. Think of the exposure as an accumulation of photon hits over time. If the light is feeble and the exposure is super long, the photons are coming into the camera, one by one with a pause between each. Such a prolonged exposure allows time for the light sensitive reaction to heal. In other words we calculate an exposure by the Law of Reciprocity to be 6 minutes. However we find that this results in an under-exposure because of the healing of the reaction due to the long interval of photon hits. Thus we need to add time to the exposure to compensate. Now we are talking about the failure of the Law of Reciprocity when the exposure time is elongated.

 

 

Conversely, if the exposure time is super short 1/1000 of a second or quicker, we again encounter a failure of the Law of Reciprocity. This time, the photons are coming is very rapidly. Each hit creates a reaction but before this reaction is fully realized, the next hit occurs. Thus the effectiveness of each hit is reduced. To mitigate we must also add more time.

 

 

 

In short, reciprocity failure is a reduction of the ISO and this occurs both a very fast and very elongated exposure times.

 

 

Astronomers, with their super elongated exposure have figured out ways to mitigate. Telescope cameras using film, have chambers that can accept dry ice. This super cools the film during the exposure and this mitigates reciprocity failure. Also, astronomers pretreat film by baking in an oven filled with special gasses. This method also mediates reciprocity failure for film. The digital chip does not experience reciprocity failure however the digital camera is plagued with noise and saturation and photosite leakage. That’s a whole different story.

There is "reciprocity" like what your initial post was talking about, e.g. f/4, 1/125th, ISO 100 produces the same exposure as f/5.6, 1/60th, ISO 100. Then there is "reciprocity failure" where that no longer holds true at very long or very short exposure times because of how file emulsion responds to extreme exposure times.

Thanks Alan.

I always appreciate your contributions here.

OK so I asked a photographer friend about reciprocity and he said it's basically adding exposure time to low light photography using different ISO films...

 

- The practicalities are correct, but technically your friend is wrong.

 

As Alan explained; the term 'reciprocity' is inaccurately used as shorthand for reciprocity failure, or reciprocity law failure.

 

The exposure triangle relates time (shutter speed) to light intensity (aperture and brightness of light). These two variables normally have an inversely linear relationship in order to keep exposure constant.

 

E (Exposure) = I (Intensity) x t (Time)

 

As light intensity increases, time must be reduced in order to keep a constant exposure. Thus t = E/I and I = E/t. This inverse relationship is where the term 'reciprocity' comes in, and this reciprocity law holds over a range between about 1/2000th of a second and 1 second or so shutter speeds. Those aren't hard and fast figures, and depend on the type of film and the intensity of light - generally a datasheet or table needs to be consulted.

 

To complicate things a bit more: This reciprocity law failure isn't strictly a function of shutter speed, but of light intensity.

 

Film slowly loses its 'latent image' (the invisible image captured before development). As a consequence, when the light hitting the film is at a very low level, the latent image degrades almost as fast as it's created - exactly like trying to fill a leaky bucket. So 'long exposure' reciprocity failure should really be called low intensity reciprocity failure.

 

Likewise with high intensity exposures. The film basically just can't react fast enough to a very short burst of high intensity light.

 

As a result, both high and low intensity exposures break the reciprocity law and result in less exposure than expected from the formula E=It.

 

There is a subtle difference in the way film reacts however. High-intensity (short time) exposures decrease contrast, while low intensity (long time) exposures increase contrast, even after compensating by increasing the exposure.

 

Digital sensors suffer no such 'reciprocity' effects and need no compensation at any practically encountered exposure intensity or time.

 

"...however the digital camera is plagued with noise and saturation and photosite leakage."

 

- Which is why no professional astronomer today uses film?

Digital sensors also benefit immensely from cooling; using Peltier devices or even liquid Nitrogen.

Edited December 20, 2018 by rodeo_joe|1

Wow, great answers! Thanks especially to Alan & Joe for your in-depth replies & for sharing your knowledge, but thanks to all for taking the time.

 

To address the other question, or part of the equation, why would some of my shots be grainy? The grainy images were shot mid day, either in sun, or hazy sun, (Portra 160) or on a reasonably bright cloudy day, in the case of the Ilford HP2 C41 B&W film. (I will confirm that film for these shots)

Old film?

 

Also, happy to put some of the grainy images up for you to see, if that is helpful.

Seeing the images would help a lot with diagnosing the problem, although scan quality could be a bigger problem than the film itself.

I agree with AJG - many photographic scanners are sh!t. They can be very quick, while offering good resolution, such as the Kodak Plustek F135+. But they usually end up giving you grainer scans than you would get with a scanner like the very expensive Flextight X5. If you can access a cine scanner, that would be even better. I've seen scans of pushed 500T S16mm film and they looked surprisingly good considering how small a 16mm frame is.

Ok here are the scans. 1st image with the Portra 160

 

Here's one with the Ilford XP2 Super film, which I thought was teh C41 process B&W?

 

Oh and before I get any further, these are scans from the processing lab, Richard Photo Lab in Los Angeles. I had asked online for recommended labs and after looking around a bit, chose these folks. I've chosen their medium quality scans-18mb, approx. 2050x2790 pixels or higher. The scans were downloaded into my Mac desktop, and using the native apple post editing software, I auto-balanced the light, levels, and curves in both the color & B&W shots.

 

This B&W shot looks OK from this distance but gets really grainy when you zoom in on it.

 

OK sorry for the double post above, was trying to delete the "thumbnail" pic but couldn't seem to do it... anyway these are the shots before and after that pic of my GF and. our. 2 friends. Neither seem as grainy although, zoomed in they get grainy... maybe its just a scan thing. I think these were scanned on a Frontier scanner. Richard also offers Noritsu scanning, and for a higher fee, will drum scan as well.

 

Also, maybe this is just my imagination and if I decided to print these they'd be fine.

This B&W shot looks OK from this distance but gets really grainy when you zoom in on it.

 

- Of course it does. It's 400 ISO film.

 

The gritty Portra 160 looks severely underexposed to get that level of grain. What do the negatives look like. Very thin I'm guessing.

 

Are you sure the XP2 was given C41 processing? If it was put through B&W chemistry it'll be grainier, and the structure doesn't look like dye-clouds to me, more like silver 'grains'.

 

"I've chosen their medium quality scans-18mb, approx. 2050x2790 pixels or higher."

 

- Those pixel numbers don't make much sense for a square format.

Edited December 21, 2018 by rodeo_joe|1

For a point of comparison, here is an earlier scan from a roll of Tmax 400. I had Richard make me a large, 16" X 16" print of this and it's pretty amazing, even t ho the scan does get a little grainy when zoomed in. My Mac zoom slider function does zoom to 400% so that's pretty radical... the print is on Fuji Pearl and is particularly lovely, well suited to this image, IMO. No sign of any such graininess.

 

- Of course it does. It's 400 ISO 35mm film.

 

The gritty Portra 160 looks severely underexposed to get that level of grain. What do the negatives look like. Very thin I'm guessing.

 

That's what I was wondering. Yes, pretty thin... OK as. it happens, I made notes on this portrait shot. SO wow, this was shot at F/22, shutter speed of 125. It was bright, Alternately sunny with clouds moving across the sun. Clearly the sun was shining ion the garage door n this shot. Now I'm learning and stuff but I know enough by now to know that these numbers are wrong.

the 80mm f/2.8 lens goes from f/16 to f/11 with a single interim click between the two.

 

I guess I was trying to shoot with the number 160 in mind? in my notes, I have "ISO 100" written. Not sure what I was doing. Ha ha. Clearly.

SO I guess this is part of what I am trying to figure out: How to handle a film with an ISO of 160 VS a film with an ISO of 400. I mean, as of now theses are the only 2 f ilm ISOs I've shot. Without being able to really articulate the question, or even fully formulate it in my mind... I guess I wonder, are various ISO films good only for certain conditions, or can you shoot any film any time under any conditions?

Grain explained: The chief ingredient for film is light sensitive crystals of a silver compound. There are three. Silver iodine (lest sensitive), silver chlorine, and silver bromine (most sensitive). Photo films are can be just one of these or maybe a mingling. These are called salts of silver or silver haloids. Iodine, chlorine, and bromine are a family of elements nicknamed the halogen family (Swedish for salt maker).

 

 

The three silver halogens resemble table salt except they are far smaller than salt crystals. A clear film base is coated with unflavored gelatin. This gelatin is the binder (glue) that affixes the silver salts. These silver salts are not stable. When hit by photons the bond that holds them together is broken or weakened. The camera exposure only weakens.

 

 

The exposed film is then submerged in a developer. This solution is able to single out exposed vs. unexposed crystals. The developer splits (reduce) exposed crystals into their two component parts. The halogen portion is liberated and it is dissolved into the waters of the developer solution. The silver portion remains imbedded in the gelation. This is the metallic silver that makes up the opaque image you see on the finished film. The developer does nothing to those crystals that were not exposed (however if the film is allowed to remain in the developer for a prolonged period, they will also be reduced).

 

 

The film is then rinsed to stop the action of the developer (stop bath). The film is then submerged in a fix solution. This bath dissolves un-reduced silver salts and leaves undisturbed metallic silver. The film is then washed to remove residual chemicals.

 

 

The gain you see is a clumping of the flakes of metallic silver. The images you see on all films sport a structure that we call grain. The size and thus the visibility of grain is a function of nature of the type and size of the original silver salts, plus, how the film was developed. There are a numerous different developer formals. Some yield trifling size metallic silver masses, others larger clumps. Many things effect grain size. High ISO films contain more and perhaps larger silver salts. Low ISO films contain less and smaller silver slats. Over-exposure tends to yield more noticeable grain. Mundane areas like empty sky show more grain than busy areas with details.

 

 

If we use film, we are plagued by grain. Some love the grainy image others adore.

The gritty Portra 160 looks severely underexposed to get that level of grain. What do the negatives look like. Very thin I'm guessing.

 

Yep, I agree.

 

Something to understand about color neg films is that virtually all of them use multi-layered coatings for each color - one layer will be more sensitive to light by virtue of having larger "grain." The less sensitive layer(s) will have finer grain. In the initial stages of the exposure, the more-sensitive larger crystals are predominantly affected, with the less-sensitive layers gradually getting more and more exposure, helping to "fill in" the "grainy" areas.

 

The net results is that areas of the (color neg) film that are barely exposed have a much coarser grain structure. You might wonder, "Well, if it's always there, why don't I see it in more of my images?" The answer, in normal printing, is that these parts of the image are so dark, nearly black, that the graininess is not seen. But if the negative is heavily underexposed then it is usually printed lighter, so that the mid-tones are sort of ok. Consequently the intended shadow areas are some lighter tone (rather than near-black), and the grainy texture is very apparent.

 

I can't say much about the scanning operations - I have relatively little personal experience - but in your example I'm pretty sure that the scanner processing operation has really aggravated the grain.

 

If you want to test this yourself, next time you are shooting something like this (with deep shadows) try wasting a little film on an exposure series, making sure that at least one shot is underexposed by 2 f-stops, or a bit more. It should end up significantly grainier than those that are normally (or over) exposed. Remember, though, that to see this graininess the scene must have some dark areas in it (if your scene has only mid-tones, or lighter, graininess won't show up).

I guess I wonder, are various ISO films good only for certain conditions, or can you shoot any film any time under any conditions?

 

Well, first, color films are designed for a certain "color-balance" in the light. Today nearly everything is designed for a "daylight" balance. So if you give a "correct" exposure, each of the three color-sensitive layers - one sensitive to reddish light, one to greenish light, and one to bluish light - will be more or less properly exposed. But if you use an "incorrect" light source there can be problems. For example, if you shoot a daylight-type color film under "tungsten light," the amount of bluish light will be roughly two f-stops too weak. Consequently the blue-sensitive film layer will be relatively underexposed. So the general rule is to use the color film under the correct lighting. If the light has the wrong color makeup you would generally want to increase the exposure so as to avoid underexposure in any of the color layers (color neg films generally have a lot of leeway for overexposure).

 

That aside, the main reason to use a different ISO-speed film is because of the exposure difference. A 400-speed film is 2.5 times more sensitive than a 160 film, so it allows a shutter speed 2.5 times faster. This doesn't seem like much in many cases, but if you you are getting down into shutter speeds of only about 1/30 second, it can really help a lot to get up to 1/60, or perhaps 1/90 second.

 

My personal view is that I like to shoot the slower speed film, if possible, for the finer grain. But if I already know that I'm not gonna be enlarging too much, where grain will not be an issue, then the higher speed film is probably preferable because it has 2.5 times the motion-stopping ability due to the faster shutter speed.

All this is really interesting, guys thanks so much for sharing!

For the record, I'm not opposed to grain, per se... in fact that one shot from the roll of Portra, I think, looks OK simply because the content is a little gritty by its very nature. As it happens that garage is not too far from home so I can go shoot it again any time. I thought the faded colors w Ould be nice for that old Portra 160 so maybe I'll get some more and try it again.

Out of curiosity, on that shot of the garage that I underexposed, what would you guys shoot it at using a 160 speed film?

 

 

Thinking about lighting and film, I am thinking about doing some portraits of some friends, and have asked another photographer friend (aforementioned) if I can use some of his lighting stuff. I guess If I'm going to shoot any color film then I better make sure the film matches the lighting elements. I was just reading about film & tungsten VS LED lighting in Lee Frost's book of low light & nighttime photography so this info is timely and helpful by way of imprinting, I guess! BUT shooting black & white film, since it wouldn't be color balanced, any lighting is OK, then, yes?

Out of curiosity, on that shot of the garage that I underexposed, what would you guys shoot it at using a 160 speed film?

 

Hi, it's hard to guess accurately without seeing (or measuring) the actual film, but I'd guess at least one, and more likely closer to two full f-stops. I'm judging this largely on the basis of that brick wall on the right side. When it goes into shadow, all of the detail is lost - even the "white" mortar between the bricks disappears. I just don't think this would happen at one stop under, so I'm guessing two stops.

 

I guess If I'm going to shoot any color film then I better make sure the film matches the lighting elements.

 

Well, a lot of people shoot color film under off-spec lights with not-too-bad results. It's largely sort of correctable provided that you don't let any of the film's colors layers "bottom out" on the "characteristic curve," another way of saying that none of the three color layers have gone seriously underexposed.

 

If you wanted to shoot high quality portraits using tungsten lighting (with a daylight film), you'd probably be best off using the proper color balancing filter on the camera. But lacking the filter, the next best thing (short of using a flash) is probably to overexpose by about two stops to keep the blue-sensitive film layer adequately exposed. It might be better to let the final image to go slightly yellow/orange to give the impression that it was shot under "warm" lights.

 

BUT shooting black & white film, since it wouldn't be color balanced, any lighting is OK, then, yes?

 

Sure, should be fine. There would probably be some subtle tone shifts in the same way that colored filters behave (the rule is that a filter "lightens its own color"). But unless you are using strongly colored lights it's probably no big deal.

OK, Apologies for falling away from this for a couple days, but I have lingering questions in the area of film speed...

 

I was reading something about doing a test of film in your camera. It began by talking about what they called "box speed". I think it was with Trix 400 and they began with F4 @ 1/125? then went up and down from there... So, box s peeps. What would the box speed for say 160 portraiture be and tho I don't recall seeing any such info on the actual box, aside form something so obvious, is there a formula for standard for jousting box speeds on film? I assume "box speed" refers to ideal camera setting for a given film under certain or ideal conditions?

 

Thanks guys.

Tom