Understanding characteristic curve

David Allen said:

1. Find a scene with with a good range of tones
2. Using the box speed, meter the darkest area in which you wish to retain shadow detail
3. Move the camera so that you are only photographing this shadow area
4. From the meter's reading close down the aperture by 2 stops or increase the shutter speed by two stops and then expose 6 frames at: the given exposure then +1 stop, +2 stops, -1 stop, -2 stops and -3 stops less than the meter has indicated

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David,

If I'm reading you correctly, in step 2 I meter a shadow. Then in step 4 I underexpose by 2 stops from the meter reading, and use this as a baseline for the remaining exposures. So the net exposure from the metered exposure in step 2 for the series of 6 exposures, is -1 (-2+1) 0 (-2+2), -3(-2-1), -4(-2-2) and -5(-2-3)?

Craig said:

David,

If I'm reading you correctly, in step 2 I meter a shadow. Then in step 4 I underexpose by 2 stops from the meter reading, and use this as a baseline for the remaining exposures. So the net exposure from the metered exposure in step 2 for the series of 6 exposures, is -1 (-2+1) 0 (-2+2), -3(-2-1), -4(-2-2) and -5(-2-3)?

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Metering the shadow gives you a reading that is roughly 4 stops more exposure than you need, then reducing the camera setting by 2 still puts you 2 stops over normal.

I’m all for avoiding underexposure but that is overkill IMO.

Ted, 1.5 is the integral of the curve. You are correct in assuming that 1.0 is the desired value but the human eye integrates the curve and the result requires a starting value of between 1.5 and 1.8.

Mr Bill, sensitometry is very useful if you keep at it.

Remember that actual speed is the inflection point of the curve. You measure it by drawing a straight line along the X axis at the fog level and then looking for the first change in density that moves upwards. Any other change is a chimera that is related to contrast effects and toe effects.

PE

PE: earlier you mentioned a contrast index for film is 0.6-0.7. Is that where the Kodak recommendations for development are aiming? I can't find it now, but I thought I read somewhere of an aim point of 0.55-0.58. That might not have been Kodak literature though.

Empirically, some of my negatives seem thin in shadow areas, so I probably do need to do a bout of film testing. Or just bump development times 20%!

I've recently been using a package of Efke Ortho sheet film and had great success. Very high contrast, but the pictorial results are excellent if shot on an overcast day.

EDIT: I found it. The developing time guidelines are for a CI of 0.56, Publication L-9, 1994.

Craig said:

...some of my negatives seem thin in shadow areas, so I probably do need to do a bout of film testing.

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How do they print?

If the prints are good (good detail where you want it and the contrast/snappiness you like) they are not ‘too thin’.

I’m not trying to discourage your testing just trying to make it productive.

A negative that is truly too thin would either lack the shadow detail you want or contrast would not be correctable with paper grade. Do you have either of those problems?

Thanks Craig,

I couldn't find it right away but 0.56 sounds right.

I got interested in film testing because, like you, some of my legacy negatives are thin in shadow areas. I wanted to have better control.

Looking back, I think my inconsistent results were because I used automatic exposure a lot. Average metering is easily tricked into underexpose, for example when you include light sources in the frame.

I've told this story how I used my understanding of characteristic curves to decide on a development time for some pictures I took a few weeks ago...

Being caught up in the moment, I only took one quick exposure reading. I spot metered off my hand (good) but forgot to "place it on Zone VI" (oops 1 stop underexposed)... then I switched from an f/1.4 lens to an f/2 lens (oops another 1 stop underexposed)... luckily I dialed in 250 for the 400 speed film (good, 2/3 stop more exposure)... Total underexposure mistake 1 1/3 stop.

Knowing that I intended for my meter reading to "fall on Zone VI", I could trace a line across my graph where I would have liked that meter reading to fall in terms of density. Knowing the mistakes I made, I looked 1 1/3 stop "to the left"... and looked for a curve that came close to bringing me to that density...

Then I picked a development time that was right for those rolls of film. It worked out well...

markbarendt said:

How do they print?

If the prints are good (good detail where you want it and the contrast/snappiness you like) they are not ‘too thin’.

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They print ok. Not amazing, but acceptable. I use the RH designs F stop timer combined with their zonemaster and I'm usually printing grade 3.5-4 to get a "nice" print with a full tonal range. Not always, sometimes it comes up beautifully on a grade 2.

I do a lot of mountains in Western Canada and there can often be little detail in the forest. I can usually get the contrast I want (I think!) and can print on available paper grades.

What started me thinking was I recently got some lessons in Lightroom from a friend of mine and he worked over some digital shots I had taken. I did one on the digital and one on the 4x5 of the same scene. The digital came out to be amazing, and the 4x5 looks muddy and flat in comparison after a fair bit of darkroom work. I've been printing for 25 years now, and I've always been a better printer than negative maker. I can usually make others negatives sing, and never my own. Thus I figured it's time to take a hard look at my negatives.

Bill,

I played around with the zone system a few years ago, and 99% of the time I ended up with the same exposure as my Nikon suggested on matrix metering. So I usually use that meter reading at box speed and develop using the recommended times. I always get something printable, but as mentioned above I feel the shadows could be a bit thin.

Craig said:

Empirically, some of my negatives seem thin in shadow areas, so I probably do need to do a bout of film testing. Or just bump development times 20%!

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Fyi, changing the amount of development has only a small effect on the shadow areas. So if you want to change the amount of shadow detail you're better off to change the exposure.

Ps, update: seeing that you have 25 years of printing under your belt, you probably already know this.

Examples of the photos I was talking about. The wet print I can still wring more out of the negative, but it was a decent effort. Certainly a long way from a straight print.
I took a picture of it with my phone, so it's not the greatest reproduction, but not bad compared to the paper print. A good representation anyway.


And this is the digital image which I would really like my 4x5 print to look like! I've not been able to get the separation in the trees on the wet print

Sounds normal Craig,

Knowing that the rated speed is intended to give you "the least" exposure to get an excellent print, it's easy to think of giving 2/3 stop more exposure. It's just good insurance. (If you don't ruin the picture by having too long a shutter speed or not enough depth-of-field).

You should be able to use the RH Designs equipment as a densitometer. Right? At least having that equipment on hand, you have some sophisticated technology that you could put to the task of making better negatives.

Can you get a test strip section of the trees to show detail you want (even if you can't get the whole picture to look good)?

If you can't because the detail isn't there, then yes... more exposure would have helped.

Craig said:

David,

If I'm reading you correctly, in step 2 I meter a shadow. Then in step 4 I underexpose by 2 stops from the meter reading, and use this as a baseline for the remaining exposures. So the net exposure from the metered exposure in step 2 for the series of 6 exposures, is -1 (-2+1) 0 (-2+2), -3(-2-1), -4(-2-2) and -5(-2-3)?

Click to expand...

Yes that is correct. When the meter 'sees' only the shadow area it will indicate an exposure to achieve a middle grey (Zone V in Zone System terminology) but this should be rendered as a very dark grey with some detail (Zone III in Zone System terminology) so the correction required is to reduce the exposure indicated by the meter by two stops.

Bests,

David.
www.dsallen.de

markbarendt said:

Metering the shadow gives you a reading that is roughly 4 stops more exposure than you need, then reducing the camera setting by 2 still puts you 2 stops over normal.

I’m all for avoiding underexposure but that is overkill IMO.

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Mark I do not understand your assertion about metering the shadows gives a reading that is 4 stops more exposure. That would only be true if we were trying to set Zone I - which is not the purpose of this testing regime. The purpose is to identify the correct EI that will render Zone III as a dark shadow with detail so that, in the field, one merely needs to meter the shadow area where one wants to retain detail and use that to set the exposure.

Bests,

David.
www.dsallen.de

The wet print doesnt look contrasty enough which suggests either needs harder grade or if thats maxed out then more development of negative but that could just be phone doing that.

As bill said do a test strip of trees at front and see if you can get them in a place you like then see where you are with rest of scene.

Looks gorgeous there.

Craig, What paper are you using? Ilford Multigrade, printed sky=>soft, with a hard light punch, and foreground=>hard, should be able to match the digital file, at least a lot closer than the print you're showing here. (lovely image, btw)

Craig said:

Thanks Mark, that helps. I was getting fooled by the "relative" portion of the log exposure scale, I thought that it had been normalized and film speed accounted for. If it hasn't, than makes much more sense in the way the curves are shifted.

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Realized I didn’t answer your first direct question... Right, they are not normalized for the film speed.
The scale of relative exposure is logarithmic. Each unit is a factor of 10. Film speeds 50 and 500 are one unit apart on that scale. (Your two films are 50 and 400 which are 0.9 apart). So the 400 speed film is nearly one scale unit more sensitive to light than the 50 speed film.

Craig said:

PE: earlier you mentioned a contrast index for film is 0.6-0.7. Is that where the Kodak recommendations for development are aiming? I can't find it now, but I thought I read somewhere of an aim point of 0.55-0.58. That might not have been Kodak literature though.

Empirically, some of my negatives seem thin in shadow areas, so I probably do need to do a bout of film testing. Or just bump development times 20%!

I've recently been using a package of Efke Ortho sheet film and had great success. Very high contrast, but the pictorial results are excellent if shot on an overcast day.

EDIT: I found it. The developing time guidelines are for a CI of 0.56, Publication L-9, 1994.

Click to expand...

A gamma or CI of motion picture film is 0.55-0,58. This is due to the longer latitude of the print films. The films intended for printing on paper are higher and shorter in latitude due to the limitations of paper.

PE

dwross said:

Craig, What paper are you using? Ilford Multigrade,

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Yes, Multigrade. In this particular case, satin finish in 11x14. My usual is MG cooltone gloss.

I'll get back into the darkroom this weekend and make a test strip of the trees and see what I can do with them.

Sorry it's taken a while to get into the darkroom. I had a good look at the negative and there is shadow detail in the trees. Some of the other negatives I made that day are completely clear in the trees, so underexposed I think. I bought some film, so I will do some of the testing suggested here.

Tree test strip: Ilford multigrade IV, printed at grade 4. test strip photographed with my phone, but it's a good representation of the shadow detail:


Full print, also on gloss MGIV. Main exposure grade 4, 14 seconds, trees burned in an additional 7 seconds at grade 4.5. I think this print has come up much better, with a bit more work it will be very nice.

Looks like it's coming together and you're getting the trees!