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MartyNL
12th March 2011, 11:59 PM
I can't recall when I heard of this and I don't know if it's true or just another one of those darkroom myths, but...

Does halving the exposure and opening the aperture increase contrast. By that I mean, a brighter but shorter exposure giving higher contrast than a darker and longer exposure?


I've never seen anything scientific about this and was just wondering if there are any grounds to suppose it being true...

cliveh
13th March 2011, 12:23 AM
No it does not.

RayHeath
13th March 2011, 12:48 AM
Hey Martin

Not if the exposure is exactly the same. Why not try it for yourself?

Richard Gould
13th March 2011, 08:37 AM
No, it simply decreases the exposure time, makes no diference to the contrast,Richard

Dave miller
13th March 2011, 09:50 AM
I'm with the others.

Vania
13th March 2011, 11:50 AM
I don't know if it's what you mean but there is a trick more effective with fixed grade paper but, that still works with VC too for in between grades. Basically overexposure and under development increase contrast and the reverse decease it. This is the reason why your "normal" prints should not stay in the developer for it's full development potential. It gives you flexibility to be able to develop more or less if you need to fine tune contrast.

JimW
13th March 2011, 12:10 PM
Agree with the respondents. Check it out with film. Reciprocity works. 1/500 at f8=1/250 at f11. No change in contrast. However, altering exposure AND development does alter contrast, pushing/pulling films. Same with paper.

Kev M
14th March 2011, 10:49 AM
I've read a similar thing in magazines where people say they've changed the aperture/shutter (can't remember which they said) to alter the contrast (but altering the other to maintain the same exposure value).

I wonder if there is some truth in it, after all, I've noticed that contrast changes when printing as the exposure times get longer so what says that the same doesn't apply to the film or sensor?

RayHeath
14th March 2011, 11:28 AM
I've read a similar thing in magazines where people say they've changed the aperture/shutter (can't remember which they said) to alter the contrast (but altering the other to maintain the same exposure value).

I wonder if there is some truth in it, after all, I've noticed that contrast changes when printing as the exposure times get longer so what says that the same doesn't apply to the film or sensor?

OK, so go and do some tests and let us all know the results.

Just don't confuse changes in print density with changes in contrast.

Martin Aislabie
15th March 2011, 07:23 PM
Paper, unlike film, is developed almost to completion.

Therefore extending the development time of your paper will yield very little extra increase in density or gamma.

Of course you can snatch a print early from the developer to reduce the full density building up, which is the equivalent of pulling in film.

Film isn't developed to completion, so you can push and pull with exposure and/or development compensation

However, for the very curious mind there is nothing like trying it for yourself :)

Martin

cliveh
15th March 2011, 08:21 PM
Paper, unlike film, is developed almost to completion.

Therefore extending the development time of your paper will yield very little extra increase in density or gamma.

Of course you can snatch a print early from the developer to reduce the full density building up, which is the equivalent of pulling in film.

Film isn't developed to completion, so you can push and pull with exposure and/or development compensation

However, for the very curious mind there is nothing like trying it for yourself :)

Martin

Martin, he isn't referring to development, but exposure.

FrankB
15th March 2011, 08:55 PM
I have to go with the crowd on this one.

Kev M
16th March 2011, 01:57 PM
OK, so go and do some tests and let us all know the results.

Just don't confuse changes in print density with changes in contrast.

Are print density and contrast not linked then?

If you agree that changes to print exposure by balancing aperture and time are non-linear then what says that film isn't the same?

Dave miller
16th March 2011, 02:46 PM
Are print density and contrast not linked then?

If you agree that changes to print exposure by balancing aperture and time are non-linear then what says that film isn't the same?

I'm not sure that I do agree "that changes to print exposure by balancing aperture and time are non-linear", at least within practical limits, please amplify. :confused:

RH Designs
16th March 2011, 03:44 PM
Are print density and contrast not linked then?

If you agree that changes to print exposure by balancing aperture and time are non-linear then what says that film isn't the same?

Print density and contrast are indeed linked - contrast is an expression of density range. But simply increasing density (i.e. exposure) does not increase contrast, it just makes the whole print darker.

Both film and paper exhibit reciprocity failure which means that balancing a change in aperture by an identical change in exposure does not necessarily produce the same result. And reciprocity failure is not linear!

cliveh
16th March 2011, 09:09 PM
Just to play devil's advocate with Marty’s original question, if you wanted to be pedantic, perhaps Sabattier would provide different contrast ratios as high energy exposure levels increase (flash), as this could perhaps be evident with higher contrast levels at Mackie line boundaries. However, I guess this doesn’t really count, as the film or paper has already started to develop.

Kev M
17th March 2011, 08:59 AM
I'm not sure that I do agree "that changes to print exposure by balancing aperture and time are non-linear", at least within practical limits, please amplify. :confused:

If I make a print at F4 at a given time and then stop down to f22, then add 5 stops to my exposure time then I've found that in my limited experience I don't end up with two identical prints. Hence my statement that a balanced adjustment doesn't always end up with the same print, to achieve an identical looking print would require either the aperture or exposure time to be adjusted in isolation to the other hence it's no longer a linear compensation.

Or perhaps it's just my printing.

Dave miller
17th March 2011, 09:13 AM
If I make a print at F4 at a given time and then stop down to f22, then add 5 stops to my exposure time then I've found that in my limited experience I don't end up with two identical prints. Hence my statement that a balanced adjustment doesn't always end up with the same print, to achieve an identical looking print would require either the aperture or exposure time to be adjusted in isolation to the other hence it's no longer a linear compensation.

Or perhaps it's just my printing.

No, not your printing, that's an extreme change, I was thinking of a stop either way which would be the sort of adjustment that I might make.

Tony Marlow
17th March 2011, 10:28 AM
Both film and paper exhibit reciprocity failure which means that balancing a change in aperture by an identical change in exposure does not necessarily produce the same result

With my non-scientific way of working I have found, when enlarging, that if I change the aperture by one stop, a one stop change in exposure time will not give the same result with the print.

Tony

Dave miller
17th March 2011, 11:31 AM
With my non-scientific way of working I have found, when enlarging, that if I change the aperture by one stop, a one stop change in exposure time will not give the same result with the print.

Tony

There are other factors to consider including the accuracy of the calibration of the lens aperture iris.

RH Designs
17th March 2011, 12:00 PM
If I make a print at F4 at a given time and then stop down to f22, then add 5 stops to my exposure time then I've found that in my limited experience I don't end up with two identical prints. Hence my statement that a balanced adjustment doesn't always end up with the same print, to achieve an identical looking print would require either the aperture or exposure time to be adjusted in isolation to the other hence it's no longer a linear compensation.

Or perhaps it's just my printing.

No it's not you, it's reciprocity failure. It's a measurable effect and our Analyser and ZoneMaster compensate for it.

Mike O'Pray
17th March 2011, 12:02 PM
I have tried this by setting the probe on a set part of the neg and waiting until the exposure settles in the timer, then changing the aperture setting. When I do, the time then shown for even 1 stop down or up is never half or twice what it was and the bigger the f stop difference the more it deviates.

I have never bothered to do a set of prints this way but I suspect that while one stop either way might not be enough to show a difference( I think it is Ralph Lambrecht who reckons it has to be at least 1/12th of a stop for the human eye to spot the difference) then by the time you get to two aperture stops difference I suspect it is of this order that allows the eye to see the differencec.

I might have a go tonight.

Mike

RH Designs
17th March 2011, 12:41 PM
In "Way Beyond Monochrome" there is a discussion of paper reciprocity failure. For Agfa MCC it's about 1/16 stop per stop of exposure change, with a contrast change of only 1/4 grade over a five stop range.

Paul.
20th March 2011, 12:24 PM
Now a poor workman would claim this is why he can never get 2 prints the same.
Paul.

DavidH
20th March 2011, 10:49 PM
Going back to Dave's "practical limits" point, is it not true to say that the contrast of light transmitted through a lens tends to reduce a little if stopped right down? The lens tests that used to be published in magazines indicated so, and it seemed to apply just as much to enlarging lenses as to camera lenses.
My own experience seems to bear this out. I was given to understand many years ago that reciprocity failure on printing paper only tended to become apparent with very long exposures.