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Other than ISO, what causes grain?

David Liu , Feb 03, 2008; 08:58 p.m.

I have a basic question about grain, and what causes it other than ISO. I've done extensive google searching on photo.net and the internet in general to no avail. I'm aware that high ISO films will have higher grain, but with film and developing conditions identical, are there any other factors that contribute to grain? In my last roll of film of Ilford HP5+, I took a picture outdoors in plenty of sunlight (1/125, f16), and another indoors with limited light (1/2 sec, f8). Sorry, I don't have access to a scanner to scan them in, but both were exposed properly, in the sense that fstop and shutter speed gave identical metering readouts. However, the outdoors photo had significantly less grain in the final 8x10 print than the indoors one. Since this was on the same roll, the ISO and developing conditions were obviously the same, but I don't understand why the indoors photo would have much more grain.

I've read that low light conditions can contribute to grain. Is this a factor independent of ISO? In the indoors picture I needed a 1/2 second exposure to take the picture -- would the longer exposure time required to expose the negative be the cause of the grain? This would seem unlikely because I've read that barring lens imperfections and reciprocity failure, the same photo with different fstop/shutter speed combinations won't affect grain/quality.

So I'm pretty confused why I'm observing different amounts of grain. I would appreciate any help or insights you could give.

Thanks!

Responses

Jeff Adler , Feb 03, 2008; 10:30 p.m.

ISO by itself does not cause grain. If I use Tri-X in a medium format camera and make an 8X10 I can have a print with very little grain. Higher speed films tend to have more grain because the particles of silver which capture the image are larger. Many things can affect grain and some things which people think affect grain do not. Overexposing the film can increase grain. Overdeveloping the film either with time or too much agitation will also increase grain. Grain tends to be more apparent in gray areas of a photo. It is less apparent in areas which are black or white. Underexposing film can also make grain more apparent. Low light conditions do not by themselves increase grain.

When light is very low it is more difficult to get the correct exposure. An area in the scene which is brighter than other parts can fool the camera's meter by inflating the reading. In very low light reciprocity failure can also be a factor in getting an incorrect exposure. It's the underexposure which causes the grain to be more apparent. Some developers also cause grain to be more apparent. This is especially true of Rodinal and similar developers. HP5+ is a nice film but it is not as fine grained as Tri-X or Neopan 400. The new T-MAX 400 is supposed to have even finer grain than Tri-X. I have some in 120 size but I have not tested it yet.

If your exposure is correct and your developing time is correct you will minimize the apparent graininess of the final image. The last link in the chain is scanning the negatives or printing them optically. Scanning can give modest improvement in apparent graininess or can make thngs a lot worse. Printing on different paper grades or on variable contrast paper with different filters will change both the contrast range and the apparent graininess of the final image.

John Shriver , Feb 03, 2008; 10:49 p.m.

Under-exposure can make an image look grainier. So does developing time and the developer used.

I'd say you should find a copy of Anchell & Troop, "The Film Developing Cookbook".

Also, due to "grain alaising" the relationship of the actual graininess of the film, and what the scans look like, can be anything but direct.

Lex Jenkins , Feb 03, 2008; 11:11 p.m.

Grain can be forced out of any film. It just takes a little work with some.

Underexposure has been mentioned. Certain films, usually faster films, will appear grainy with normal development when underexposed.

Extended development. Even when film has been properly exposed overdevelopment can bring out the grain. Combine this with underexposure and you have the classic recipe for grain: push processing. (That's not a bad thing, necessarily, just a fact.)

The type of developer. Acutance developers will enhance grain by increasing apparent sharpness. Ideally, an acutance developer combined with a fine grain film will increase apparent sharpness without grain, but it's a fine line. For example, some folks like T-Max 100 in Rodinal. I don't. It's one of the few developers that can squeeze visible grain out of TMX. Also, diluting a solvent or physical developer like ID-11 will make grain more apparent. A 1:1 dilution is a good compromise; 1:3 tends to increase grain and apparent sharpness, but I usually prefer the appearance of an acutance developer over a diluted solvent developer.

Contrast filtration during printing. This effect is sometimes overlooked. Increased magenta filtration can make grain more apparent. It can be useful to increase apparent grain when you want it, and a good thing to avoid when you don't want to see grain. Careful use of selective filtration combined with dodging/burning can help control contrast while minimizing grain. Lotsa trouble, but it works.

Some photographers report that time can influence grain. This seems less obvious to me, but I won't deny the possibility. In my experience, the reason why extended development times appear to coincide with grain is because I'm overdeveloping to compensate for underexposure. Also, I like to experiment with stand development using very dilute Rodinal, 1:200 or 1:300 (or is it 1+200/1+300?... hardly matters at that dilution). But since I've done this only with Tri-X, I can't say definitively whether there's a connection with grain. I'd need to try it with a properly exposed slow speed film.

Temperature is also cited as an influence. However, most of the examples I've seen show reticulation, not grain. Not the same thing.

PC B , Feb 04, 2008; 08:58 a.m.

Hi David, I do feel a little scarred, adding my two cents after Jeff and Lex, but I've experienced one more thing that 'helps' to enlarge grain: excessive red light percentage in the light available.

I believe it acts in 3 ways simultaneously:

1) as Lex said: contrast filtering: to emulate the impression you had back then (deep dark shadows) you are likely to dial in higher contrast. Depending on the paper you use this leads to much more pronounced print graininess.

2) aberrations of the lens wide open PLUS for the red spectrum (unless it's an apo lens). Not only Putts witnessed bigger grain in pictures from less perfectly corrected lenses (with daylight even!). Plus: usually more lens flare and lower overall contrast in the negative is being counteracted by upping paper grade even more... (see 1).

3) Red light photons contain less energy (now this is a unproven thesis!): HP5+ is a conventional film (mix of differently sized AgX crystals), on average more than one photon is needed to 'activate' a AgX crystal. Because of the low energy per photon probably even more of them (see sensitivity chart in the Ilford papers), so proportionally more of the bigger AgX crystals are likely to get activated (latent image silver), the reason simply being their bigger diameter towards the incoming light. Thus the bigger grains might be forming the printed picture almost on their own. As the latent image fades (albeit slowly!) grain with a lower number of photon-hit areas loose their latency first (stochastics). Thus again, on average (only) the bigger ones remain to build up the negative density we print. End of thesis!

Fact is that I experienced the same effect as you with all conventional 400ASA films, even with last year's TMY. Delta400 is kind of hard to interpret in this respect.

I've read on the net, that using 82A/82C/80C(Hoya advises 80B/A!) filters and pushing accordingly would lead to less grain than staying filterless. Haven't tried that yet. But interesting.

If you need to push your HP5+ give Xtol (stock or even 1+1) a chance: you'll experience much less grain than most (all?) other commercial developers (I tested D76/ID11, Microphen, and Rodinal)

Hope I helped a bit. Cheers, Pete

P.S.: If light indoors is really low, and it's appropriate in relation to your subjects or the subject lighting respectively, a faint bounce flash to the ceiling only has you work with half the ASA plus more balanced light color. This will result in often strikingly better picture quality at the end of the day.

Daniel Goodale-Porter , Feb 08, 2008; 08:58 p.m.

Lots of good stuff here. I heard once that extreme changes in ph may cause a ever so slight increase in grain. Some people swear off acid stop baths because of this and use plain water baths. I use water because it is easier. Another ol' photographer's tale??

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