PDA

View Full Version : some basic questions


05-04-2010, 06:38
Hi,

i have 2 questions:

(A)

I know that faster film, over-development causes more Grain in B&W film. What about exposure, which causes more grain ? Over exposure or Under-exposure ? I read several references here that overexposure produces grain, I googled and read a few other places but could not find a satisfactory explanation.

(B)

I have read references to Lens as "low contrast" hence more suited to B&W photographs. Is it because lower contrast lens captures more shadow details than a high contrast lens ?

thanks


raytoei

Chris101
05-04-2010, 09:07
These are my answers, those of others may differ ...

A: Thr effect of exposure on grain is more complex. It depends on what you do with the negative. Generally, a little bit of overexposure will reduce grain when printing with a diffusion enlarger. When scanning, overexposure will increase grain, as will underexposure. This is because the scanner will increase contrast to compensate for the exposure error.

B: The effect on contrast contributed by a lens, flare notwithstanding, is tiny compared to the effect of changing the development, even slightly. Flare is the exception. An uncoated or buffed lens will markedly reduce the contrast of the image it projects because of the inclusion of stray light. Some lenses use older glass and adhesives that may also scatter light and thus reduce the contrast. Compensate for this (unless you want a low contrast image) by underexposing and overdeveloping.

payasam
05-04-2010, 11:41
Chris, why not a little over-development with normal exposure? Seems to me that might be better for the shadow areas.

Chris101
05-04-2010, 13:02
Chris, why not a little over-development with normal exposure? Seems to me that might be better for the shadow areas.

Sure, that'll work. It might result in a slightly dense negative, and I tend to print dark these days, so I like thinner negatives.

Roger Hicks
05-04-2010, 14:52
More exposure = more grain with conventional film (for a given developer and contrast). With chromogenics/colour, more exposure = less grain.

More exposure = lower sharpness, always, no exception, all films.

"Low contrast": highly disputable. A 'low contrast' lens compresses the subject brightness range by lightening the shadows, i.e. it gives a shorter image brightness range (a higher flare factor). It is then a question of tonality whether you prefer (i) short image brightness range + longer development or (ii) long image brightness range + shorter development. Either can give the same negative density range.

The differences can be significant. An LF camera with well blacked bellows and MC lens can give a flare factor close to 1, i.e. subject brightness range 2.1 (128:1) is reproduced as 2.1, while an old zoom in a badly blacked/baffled SLR can have a flare factor of 4, i.e. SBR 2.1 is reproduced as 1.5 or 25:1. Obviously the latter requires much more development to give the same negative density range.

See http://www.rogerandfrances.com/subscription/ps%20subject%20brightness%20range.html for more explanation.

(I hope this is correct but I've a very old friend staying, an ex Hell's Angel, and drink has been taken. If it doesn't make sense, try again tomorrow.)

Cheers,

R.

05-04-2010, 17:25
Thanks for the link and all the replies.

Juan Valdenebro
05-04-2010, 18:16
Hi,

i have 2 questions:

(A)

I know that faster film, over-development causes more Grain in B&W film. What about exposure, which causes more grain ? Over exposure or Under-exposure ? I read several references here that overexposure produces grain, I googled and read a few other places but could not find a satisfactory explanation.

(B)

I have read references to Lens as "low contrast" hence more suited to B&W photographs. Is it because lower contrast lens captures more shadow details than a high contrast lens ?

thanks


raytoei

Here's another vision, without trying to make it others':

(A) In black and white, I think if a shot is well exposed and developed, it's not important if exposure was a bit high or low and produced a bit more or less grain: results will be close, and beautiful, both for tone and grain... It's decisive, though, in color photography, where a bit of underexposure makes us lose color, and a bit more underexposure gives us huge grain and muddy colors. Overexposure (two thirds of stop over box speed) produce clean, colorful images that represent film's character.

(B) It's not about a low contrast lens being better for black and white... It's about a low contrast lens being better for a high contrast scene, both for black and white and color... And a higher contrast lens can be better for black and white and color if the scene's a low contrast one... That's almost absolute for color, but for black and white, as we control easily our negative's contrast with exposure and development, we can make good use of a low contrast lens in a low contrast scene too, extending development, as we can also capture a high contrast scene with a higher contrast lens with a rich exposure for shadows and a short development. And in color it all depends on the kind of film used too...

Cheers,

Juan

AgentX
05-08-2010, 01:12
Chris, why not a little over-development with normal exposure? Seems to me that might be better for the shadow areas.

Not really, by my rather unscientific understanding--film's proportional response to light means that shadow areas, no matter how long you develop, will only get so dense on the negative...once you've hit that point, which you should with any proper development time (N-2 through N+2), the development time only affects the lighter tones. Highlights, however, will continue to develop to the film's maximum possible density; your development time ultimately controls how far they'll go.

Hence the old maxim, "expose for the shadows, develop for the highlights." This is the basis for Zone System photography.

If you're looking for shadow detail in a contrasty scene, slightly overexpose and shorten your development time.

gns
06-05-2010, 08:39
"More exposure = More grain"

I've heard this many times, but it doesn't seem right. At least not to any noticeable degree.

1. Look at a single enlarged negative. You have a range of exposures within that negative, but with the same development, right? Do you see a difference in the grain from the lighter areas of the picture to the darker (more exposed to less exposed)? Not very much, if any.

2. When you push film, you get more grain even though you have LESS exposure.
This is due to the longer development.
When you pull film, you get less grain even though you have increased exposure.
Due to shorter development.


Cheers,
Gary

Pablito
06-05-2010, 10:47
"More exposure = More grain"


1. Look at a single enlarged negative. You have a range of exposures within that negative, but with the same development, right? Do you see a difference in the grain from the lighter areas of the picture to the darker (more exposed to less exposed)? Not very much, if any.


Gary

No, no. You see much more prominent grain the the light areas than the dark areas. Shadow areas tend to be smoother, light areas like sky and clouds show the grain more. The opposite is true for C41 films.

Roger Hicks
06-05-2010, 12:17
No, no. You see much more prominent grain the the light areas than the dark areas. Shadow areas tend to be smoother, light areas like sky and clouds show the grain more. The opposite is true for C41 films.

Seconded. And born out with microdensitometer traces, so it ain't just subjective.

Cheers,

R.

gns
06-06-2010, 07:42
Roger,

I don't know what microdensitometer traces are. Is that how you measure grain size?
Does the grain SIZE actually vary, or are they just more visible because there are more of them in the denser areas?

With the materials I use (TX400.D76), I cannot see any great difference in grain size across an image. Of course, the apparent grain varies, but I would say it is more dependent on the surface detail of the subject than the value. Smooth areas like the sky showing the grain more than textured areas where the grain is hidden.

At any rate, whatever the effects of varied exposure on the apparent grain, they seem way overshadowed by variations in development. Hence the results of pushing and pulling which run contrary to "more exposure = more grain".

Cheers,
Gary

Roger Hicks
06-06-2010, 09:37
Dear Gary,

Pretty much what it says. Measures the variation in density on a micro scale. The more exposed areas are 'lumpier'.

All grain is 'clumping', i.e. more in one place than another.

It's easier to see grain in light mid-tones, but it's also, objectively, bigger than in dark mid-tones. That's for a given degree of development of the whole film. Developer choice, time and temperature are also very important, but that's a separate question.

Cheers,

R.