Why is B&W more forgiving than reversal?

IloveTLRs · May 29, 2007

Sorry, don't kill me here if this is obvious. I did B&W back in college (1998-ish) on a K-1000. This March I dumped digital and went back to film and am learning things (all over) again. This has also been my first time using slide film.

I'm wondering, could someone tell me why black & white negative film is more forgiving than reversal film when it comes to metering and over/under exposure? Is it simple or really complicated?

Thanks in advance

Chris Breitenstein · May 29, 2007

Its my understanding that slides are less for giving because you are eliminating a very important "point of control" if you will, Printing. Your exposure and development need to be correct because you dont have that ability to fine tune the final product.

In my limited experience with chrome, I found that 1/2 stop under produces great images. I was shooting fuji velvia 50.

Sincerely:

Christopher J. Breitenstein

Alex Hawley · May 29, 2007

I'm not a photographic emulsion chemist so I can only give a layman's answer. I believe that color film in general, transparency and reversal both, has less exposure latitude because of an inherent limitation of the emulsion chemistry and and its structure on the film base. To my knowledge, none of the major film manufacturers, with their world-class R&D expertise, has been able to overcome that inherent limitation. This even holds for instant film made by Polaroid and Fuji.

There are a couple members who have extensive experience in this field who will probably chime in on this thread with a more astute answer.

Jim Jones · May 29, 2007

Perhaps contrast in transparancies was boosted to give them more impact when properly viewed.

AgX · May 30, 2007

TLR lover,

The films you are referring to are as well called reversal but also transparency films. There seems to be no difference in this but actually, there is. However, most reversal material yields a transparency.

And this the crucial point, they are made for a certain viewing situation: projection on a screen.
(And this is independent of we are talking about colour or B&W!)

Thus you have to take into account two points:
-) contrast reduction due to the screen itself as well flare induced by a rest of room lighting;

-) the need to gain an image which is correct in its tones.

A negative may have a pleasing tonal range but lacks correct minimal or maximal densities, due to the fact that there was some latitude within the exposure range. The photographer had the chance to place that image somewhere within that range. A correction, right placement of densities, even contrast correction will be done in the second stage (optical printing).
In a transparency there won’t be that kind of correction.

All this is the reason why transparency films are designed to yield density curves that look the way they do: mirrored in relation to a negative’s curve, high dmax, and high gamma.

Looking at a transparency on a light table thus could be regarded as a slight misuse, optical printing as an even greater, and using transparencies selected on a light table to be used for offset printing…

AgX · May 30, 2007

In extension...

In extension to what I posted above, I would like to remind you of another important aspect inherent to the reversal process. If one would look at the specific curve for the transparency film in unreversing processing (of course one wouldn’t get it, but well if one used a common negative film for a homemade reversal process), one would see a larger exposure latitude than the reversed film would have gained. If one would use this to fullest in the direction of Dmax, the film coming out of first development would not yield sufficient undeveloped AgX to form the reversed image in the second stage.

percepts · May 30, 2007

because reversal is designed to capture a 5-6 stop brightness range from black to white whereas b+W can capture 13+ stops depending on the film. Typically a landscape may be 7-10 stops. If you use reversal and meter for highlights, the shadows will be blocked up as they are way too dark for the film type. This is why dawn or dusk is optimum, especially for reversal when there is a small window of time when landscape contrast will fall within the optimum range of reversal film.
Also with black and white you have much greater control over development so that you can adjust dev times to achieve the contrast you want on film. Reversal has very limited control in this regard as major changes in time also adjusts colour which is not the case for B+W.

note that reversal film creates transparencies which are upto dmax 4 which is suitable for very bright projector lights. Negative film does not need to be nearly as dense because it is designed for projection by enlarger only.
If you think about the inverse square law and consider the distance a slide projector has to project compared to the distance an enlarger has to project, then it is obvious that slide projector lights need to be much brighter and hence reversal film needs to handle that.

IloveTLRs · May 30, 2007

WOW, thanks for the informative answers

Honestly the first time I ever shot slide film was in March. Pulling those sleeves out of the envelope at the camera shop is a real treat. The only thing better than 35mm slide film is medium format slide film (6x6)

Alex Hawley · May 30, 2007

IloveTLRs said:
The only thing better than 35mm slide film is medium format slide film (6x6)

Better not look at a Large Format tranny then! Oh, wait, I'm supposed to make LF converts, not dissuade them.

Helen B · May 31, 2007

percepts said:
...
note that reversal film creates transparencies which are upto dmax 4 which is suitable for very bright projector lights. Negative film does not need to be nearly as dense because it is designed for projection by enlarger only.
If you think about the inverse square law and consider the distance a slide projector has to project compared to the distance an enlarger has to project, then it is obvious that slide projector lights need to be much brighter and hence reversal film needs to handle that.

An alternative way of looking at that aspect of this discussion is that a negative is not designed for viewing, therefore it does not need to have a density range that corresponds to the dynamic range of the eye (ie a negative doesn't have to look good). The density range of a negative or a positive (including internegatives and interpositives of course) needs to suit whatever process it is primarily intended for next, whether it be printing onto enlarging paper, onto Pt/Pd, onto print film, viewing, making a negative, or whatever. The inverse square law does not affect the relative brightness of the different parts of the image.

Best,
Helen

percepts · May 31, 2007

Helen B said:
An alternative way of looking at that aspect of this discussion is that a negative is not designed for viewing, therefore it does not need to have a density range that corresponds to the dynamic range of the eye (ie a negative doesn't have to look good). The density range of a negative or a positive (including internegatives and interpositives of course) needs to suit whatever process it is primarily intended for next, whether it be printing onto enlarging paper, onto Pt/Pd, onto print film, viewing, making a negative, or whatever. The inverse square law does not affect the relative brightness of the different parts of the image.

Best,
Helen

I think you may have misunderstood what I was saying or maybe I didn't explain it fully enough.

To project a slide to a viewing screen at some distance then the brightness of the lamp has to be great because of the inverse square law when compared to an enlarger which is projecting over a much shorter distance and to paper which is sensitive to low light levels. The transparency needs to accomodate that brightness. I was not suggesting that the density of a transparency is related to inverse square law but that because of the requirements of projection, a transparency must be of great density range. A dmax 4 transparency is 13+ stops. If you metered a projection screen would it be 13+ stops range?

Helen B · May 31, 2007

percepts said:
I think you may have misunderstood what I was saying or maybe I didn't explain it fully enough.

To project a slide to a viewing screen at some distance then the brightness of the lamp has to be great because of the inverse square law when compared to an enlarger which is projecting over a much shorter distance and to paper which is sensitive to low light levels. The transparency needs to accomodate that brightness. I was not suggesting that the density of a transparency is related to inverse square law but that because of the requirements of projection, a transparency must be of great density range. A dmax 4 transparency is 13+ stops. If you metered a projection screen would it be 13+ stops range?

No, the screen image of a transparency with a density range of 4.0 will not have a 13⅓ stop brightness range, but not because of the inverse square law. The difference between the density range of the transparency and the brightness range of the image on screen will be predominantly because of the factors that AgX has already mentioned: flare, room reflections and some small amount of ambient light being the typical main sources, interacting with the behaviour of the screen itself.

A practical example of this is seen in simple film to video transfer: one cannot reduce the brightness range of the screen image to a range that can be handled by a video camera by simply moving the screen further away from the film projector.

I'll stick with the idea that the main reason for the difference in density range between a B&W negative intended for enlargement onto traditional B&W enlarging paper, and a transparency intended for viewing by projection is not because of the difference in projection distance, but because enlarging paper is matched to a much lower brightness range than that which humans percieve as normal. We don't expect a wide brightness range for all subjects, but the materials need to be capable of it to make something like a sunlit landscape look normal. Even on a light table, a transparency of a sunlit landscape would look quite dull if the transparency had a density range of 1.0, for example.

Best,
Helen

percepts · May 31, 2007

Helen B said:
No, the screen image of a transparency with a density range of 4.0 will not have a 13⅓ stop brightness range, but not because of the inverse square law. The difference between the density range of the transparency and the brightness range of the image on screen will be predominantly because of the factors that AgX has already mentioned: flare, room reflections and some small amount of ambient light being the typical main sources, interacting with the behaviour of the screen itself.

A practical example of this is seen in simple film to video transfer: one cannot reduce the brightness range of the screen image to a range that can be handled by a video camera by simply moving the screen further away from the film projector.

I'll stick with the idea that the main reason for the difference in density range between a B&W negative intended for enlargement onto traditional B&W enlarging paper, and a transparency intended for viewing by projection is not because of the difference in projection distance, but because enlarging paper is matched to a much lower brightness range than that which humans percieve as normal. We don't expect a wide brightness range for all subjects, but the materials need to be capable of it to make something like a sunlit landscape look normal. Even on a light table, a transparency of a sunlit landscape would look quite dull if the transparency had a density range of 1.0, for example.

Best,
Helen

I think we are saying the same thing. But a transparency is designed to be projected and the reason I asked whether a metered projection screen would be 13+ stops is because I knew it wouldn't and you have confirmed that. And the reason it doesn't is because much of that density range is lost in projection which means the transparency is designed with that in mind and hence my original comment.

If you think about the inverse square law and consider the distance a slide projector has to project compared to the distance an enlarger has to project, then it is obvious that slide projector lights need to be much brighter and hence reversal film needs to handle that

and specifically:

and hence reversal film needs to handle that

so whats your point?

Helen B · May 31, 2007

percepts said:
...
so whats your point?

It wasn't much of a point, just an alternative view. If someone asked me why there was a large difference between the density ranges of a normal B&W negative and of a transparency, I wouldn't say that it was because of the distance they were projected - so I offered a different explanation. That's all.

Best,
Helen

AgX · Jun 1, 2007

Helen B said:
...because enlarging paper is matched to a much lower brightness range than that which humans percieve as normal. We don't expect a wide brightness range for all subjects, but the materials need to be capable of it to make something like a sunlit landscape look normal

Helen,

I would not say enlarging paper is matched, it just cannot yield that brightness range.

For examples, the deep blacks will still reflect several per cents of light. The whitest parts reflect only 80-90%; and this diffusely reflected. In the viewing direction the ratio will be even lower.
This has some resemblance with the effects one encounters with ground glasses. And as there some remedies could be tried. As high reflective surfaces, base with specular reflection. But of course this will provoke other problems...

A general approach to transmit a scene with high brightness range via colour paper would be to print with high contrast, try to achieve high colour saturation and present the print the way that it fills our angle of view. Or even more what makes one wander with ones eyes. Though in the latter case the highest contrast should still be visible in `one glance´ I guess.

AgX · Jun 1, 2007

Actually, hinting at that resemblance with a ground glass by me wasn't a really good idea as the diffuse refraction there causes an overall brightness issue, in paper we have got, as said, a brightness contrast issue.

bjorke · Jun 1, 2007

...because black and white don't have anything to prove. They are already the true colors of photography. With intimate knowledge of both the zenith and the depths and the potential reversals of both, forgiveness is in their nature.

AgX · Jun 1, 2007

Don't know whether this aspect was underlying the initial question, but you are right bjorke, that the abstraction inherent to B&W leads one on a field where, concerning daylight coulour vision, one hasn't got something to compare; may it be actual or from memory.

Helen B · Jun 1, 2007

AgX said:
Helen,

I would not say enlarging paper is matched, it just cannot yield that brightness range.

For examples, the deep blacks will still reflect several per cents of light. The whitest parts reflect only 80-90%; and this diffusely reflected. In the viewing direction the ratio will be even lower.
...

Hi AgX,

I think that the meaning has been misinterpreted by quoting only the end of my sentence. I was discussing the brightness range of the projected image on the paper, created by the density range of the negative. My sentence was already too long and I hoped that the reader would recognise, without me having to go into full detail, the relationhips between the density range of the negative, the brightness range of the projected image, and the dynamic range of the paper.

"I'll stick with the idea that the main reason for the difference in density range between a B&W negative intended for enlargement onto traditional B&W enlarging paper, and a transparency intended for viewing by projection is not because of the difference in projection distance, but because enlarging paper is matched to a much lower brightness range than that which humans percieve as normal."

The discussion was about the reason for the difference in density range between

a B&W negative intended for printing by an enlarger onto enlarging paper, and

a colour transparency intended for viewing by projection.

The density range of B&W silver gelatin paper (about 2.0 to 2.2 for glossy paper) does not appear to be relevant.

I apologise for my easily misunderstood English.

Best,
Helen

Alex Hawley · Jun 1, 2007

bjorke said:
...because black and white don't have anything to prove. They are already the true colors of photography. With intimate knowledge of both the zenith and the depths and the potential reversals of both, forgiveness is in their nature.

Good one Kevin. Very good. I like that!

Why is B&W more forgiving than reversal?

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