Rating Paper ISO - An Exact How To?

Fragomeni · Jan 17, 2011

Hi all. I'm working on developing a workflow for using paper negatives in-camera and one of the things I keep running into are statements regarding the ISO rating of paper vs the ISO rating of film. Many people say that the best thing to do is simply test for your in-camera paper negative ISO. The problem is that I've seen this recommendation everywhere but no explicit instructions on how exactly to do it. Can someone PLEASE provide me with clear instructions (step-by-step) on how to test the in-camera ISO of paper? I understand there is probably more then one method so please share the method you've used. I am looking for a method that will give me the most exact ISO possible. I plan on using my Pentax 1 degree spot meter so plugging in the correct ISO is important for use with the zone system.

Please limit responses to information directly relevant to the question at hand with instructions on testing. Just trying to stay on track. Thanks!

Steve Smith · Jan 17, 2011

I have heard from a few sources that paper is around ISO 6. That is about four stops slower than ISO 100 film.

I would set up for a 'normal' scene and expose for ISO 6 then expose a couple of sheets +/- two stops and see which is closest to ideal.

Once you are near to the right exposure you can bracket a bit closer to get a more accurate figure.

Another option if you are putting paper into a film holder is to remove the dark slide in steps with an equal exposure at each stage. This will give you a test strip similar to those made when printing in the darkroom.

Steve.

Christopher Walrath · Jan 17, 2011

Look for John Meadows thread for the new podcast. This edition interviews our own David William White on this very subject.

Fragomeni · Jan 17, 2011

Can you provide a link? I'll look but not sure if I'll find it. Thanks.

Fragomeni · Jan 17, 2011

Found it (there was a url link here which no longer exists). I'll check it out now.

David William White · Jan 17, 2011

I didn't technically discuss finding a rating for paper, but Steve provided a working method. The final proof is in the contact prints made from the bracketed negatives. Just remember to develop both the negatives and the contact prints to completion.

Some earnest and much more knowledgeable folks here say 6 is too low, so testing to your taste with your paper is definitely recommended.

removed account4 · Jan 17, 2011

people forget that sometimes a thin paper negative is sooo much better than a dense one
so it is important to make the final print to see what thin and dense looks like ...

Fragomeni · Jan 18, 2011

I didn't technically discuss finding a rating for paper, but Steve provided a working method. The final proof is in the contact prints made from the bracketed negatives. Just remember to develop both the negatives and the contact prints to completion.

Some earnest and much more knowledgeable folks here say 6 is too low, so testing to your taste with your paper is definitely recommended.

I had to run out of the house a quarter of the way through the podcast but I'll finish listening to it tomorrow. Sounded like some good stuff.

people forget that sometimes a thin paper negative is sooo much better than a dense one
so it is important to make the final print to see what thin and dense looks like ...

Thats the beauty of paper negs, there are just so many options of different things you can do which will have an effect of the final print!

Anyway, to all, I have a workflow that I am finalizing and am soon to test which seems very promising and should allow me to do everything I am aiming for with my paper negatives. It involves testing for the in-camera exposure ISO of the paper of choice which will allow me to use the zone system just as I would with film. Also, the testing works in a way that is directly relevant to the paper to be printed on making the exposures more accurate to the final print i.e. more control. Because paper differs from film in its inability to push or pull development (which also isn't necessary with my process) exposures are based on making multiple exposures in situations that would typically call for push or pull development with film. In these cases the final print is printed from both negatives, one made for the shadows and the other for correcting the zone placement of the highlight. In situations that call for normal exposure a single neg will typically be suitable. In theory I've worked out all the hitches and it should be effective for what I'm working on. I'll begin testing the testing process and its cohesiveness with my paper neg printing process as soon as I can stop procrastinating in the name of research. Addictive!

Thanks to all for your assistance.

banana_legs · Jan 18, 2011

Francesco,

Reciprocity failure of paper is quite extreme so you may need to make a correction for that too. Exposures up to about 15 seconds need minimal correction, but additional time is needed thereafter. I work with both lenses and pinhole and have made successful exposures that took 7 hours when the time was corrected for reciprocity. I did a set of trials a few years ago and characterised a number of papers, in particular Ilford MGIV VC. I rated the paper relative to my scanners capabilities so that if I did have trouble contact printing, I could always fall back to getting a usable scan. The colour temperature of the light will also play a role in the behaviour of variable contrast paper so you may consider repeating the experiment under different lighting conditions too.

Firstly, I always pre-flash my paper in order to help increase the dynamic range that is achievable. Primarily in 'daylight' (UK, afternoon), I rate my paper for an exposure index of EI 20 (not a true ISO value, but I consider it that way). The paper response is approximately plus/minus 2 stops of near linear response and plus/minus 2.5 stops if you can tolerate the highlights and shadows rolling off a little. The paper transition at the highlights and shadows is quite sharp.

If I add a yellow filter to the lens/pinhole, I rate the paper as EI 6 (the rating includes the filter correction factor). The paper response is now plus/minus 4 stops as only the green layer of the paper is active, but although the shadow response is quite linear, the highlights are not and there is a slow roll-off. In incandescent light (about 2500K), I rate the paper as EI 2 (no filters added) and you get about plus/minus 4.5 stops but the response is very non-linear in the highlights with a long slow roll-off.

For reciprocity, 8sec=8sec, 15sec=15 sec, 30sec=35 sec, 1min=1min 19 sec, 2min=3min 10 sec, 5min=11min45sec, 10min=35min20sec, 20min=1hour54min, 32min=4hours20min. With pinhole, I have used 2 hour exposures on a number of occasions and had ok results, the longest trial being a 7 hour exposure. The dynamic range available from the paper does reduce a little though with exposures longer than about half an hour.

EDIT: If you have a wide aperture lens and a powerful flash, reciprocity is not a worry down to 1/100 sec, however I did have issues with underexposure using 1/250 sec. I could not generate enough light to get a full characterisation at faster shutter speeds.

EDIT: All of my ratings are for development to completion in paper developer. I always seem to get uneven development with MGIV if I use diluted developer and pull the negative early. I do use graded paper and develop by inspection, but it is only blue sensitive so foliage can look a bit odd. For development by inspection of graded paper, I shoot at EI 6 (with no filters).

Best regards,

Evan

Fragomeni · Jan 18, 2011

banana_legs said:
Francesco,

Reciprocity failure of paper is quite extreme so you may need to make a correction for that too. Exposures up to about 15 seconds need minimal correction, but additional time is needed thereafter. I work with both lenses and pinhole and have made successful exposures that took 7 hours when the time was corrected for reciprocity. I did a set of trials a few years ago and characterised a number of papers, in particular Ilford MGIV VC. I rated the paper relative to my scanners capabilities so that if I did have trouble contact printing, I could always fall back to getting a usable scan. The colour temperature of the light will also play a role in the behaviour of variable contrast paper so you may consider repeating the experiment under different lighting conditions too.

Firstly, I always pre-flash my paper in order to help increase the dynamic range that is achievable. Primarily in 'daylight' (UK, afternoon), I rate my paper for an exposure index of EI 20 (not a true ISO value, but I consider it that way). The paper response is approximately plus/minus 2 stops of near linear response and plus/minus 2.5 stops if you can tolerate the highlights and shadows rolling off a little. The paper transition at the highlights and shadows is quite sharp.

If I add a yellow filter to the lens/pinhole, I rate the paper as EI 6 (the rating includes the filter correction factor). The paper response is now plus/minus 4 stops as only the green layer of the paper is active, but although the shadow response is quite linear, the highlights are not and there is a slow roll-off. In incandescent light (about 2500K), I rate the paper as EI 2 (no filters added) and you get about plus/minus 4.5 stops but the response is very non-linear in the highlights with a long slow roll-off.

For reciprocity, 8sec=8sec, 15sec=15 sec, 30sec=35 sec, 1min=1min 19 sec, 2min=3min 10 sec, 5min=11min45sec, 10min=35min20sec, 20min=1hour54min, 32min=4hours20min. With pinhole, I have used 2 hour exposures on a number of occasions and had ok results, the longest trial being a 7 hour exposure. The dynamic range available from the paper does reduce a little though with exposures longer than about half an hour.

EDIT: If you have a wide aperture lens and a powerful flash, reciprocity is not a worry down to 1/100 sec, however I did have issues with underexposure using 1/250 sec. I could not generate enough light to get a full characterisation at faster shutter speeds.

EDIT: All of my ratings are for development to completion in paper developer. I always seem to get uneven development with MGIV if I use diluted developer and pull the negative early. I do use graded paper and develop by inspection, but it is only blue sensitive so foliage can look a bit odd. For development by inspection of graded paper, I shoot at EI 6 (with no filters).

Best regards,

Evan

Evan, thanks for this information on reciprocity failure. Interestingly, this is the first time that I've heard that paper's reciprocity failure can be so significant. I'd always heard that it had significantly less failure then film but no one ever really went into it in detail as you have. I found your numbers interesting and I'll factor them into my testing and my process. Who knows, you may have just saved me a lot of time. What exactly were the perimeters of your trials i.e. lighting conditions that required such long exposures? I'm very interested in this as I don't like to be limited by any lack of information. I do not initially see myself doing much night photography on paper but it may very well happen and the reciprocity failure characteristics of paper will obviously be critical in these situations. Thanks for your help!

Fragomeni · Jan 18, 2011

Also, you read my mind. When I woke up this morning the first thing I thought of was that I needed to ask about the reciprocity failure of paper. My second concern after waking up this morning was why the hell my first waking thought was about reciprocity failure! I'm losing it!

Fragomeni · Jan 18, 2011

The other question of the morning:

I'll be testing Ilford Ilfospeed RC Delux graded papers for the negatives. Using multigrade paper would vary too much in different lighting conditions and with different colors of light so to make the process as consistent as possible I'll be testing graded papers. Can anyone speak to a grade (1, 2, or 3) which offers the best overall performance and provides a contrast most effective for printing? I'll be printing on Ilford MG Fiber Warmtone Glossy by the way.

removed account4 · Jan 18, 2011

francesco

the graded paper i have shot for portraits has been agfa grade 1.
instead of taking 20 seconds ( the tungsten modeling lights through soft boxes on 300ws monoblocks )
that ilford mg fb takes, it took 3 pops of the 300ws lights ( so 1800ws), in addition to a 45 second exposure ...
i haven't used any other graded paper ( i have seagull #1 i will eventually try )

Fragomeni · Jan 18, 2011

jnanian said:
francesco

the graded paper i have shot for portraits has been agfa grade 1.
instead of taking 20 seconds ( the tungsten modeling lights through soft boxes on 300ws monoblocks )
that ilford mg fb takes, it took 3 pops of the 300ws lights ( so 1800ws), in addition to a 45 second exposure ...
i haven't used any other graded paper ( i have seagull #1 i will eventually try )

In asking about an ideal grade, I mean is there overall a best grade that generally produces the best (most accurate) contrast for printing. Performing as an in-camera neg, I'm assuming that one grade will out preform another in recording blacks and transitional tones through paper white for the purpose of printing a positive image. Also, I wont be using any studio lighting or flash. 100% natural light. I do use modeling lights in studio when doing portraits or other studio type situations but still no flash.

Fragomeni · Jan 18, 2011

Oh and specific to Ilford. If it aint broke, dont fix it haha. I plan to stick with the paper I know well.

Rating Paper ISO - An Exact How To?

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