Paper negatives

[tonyowen]

Tony, if all you get is a black image - try to move the flash further away from the paper

Agreed, but I do not understand why it is happening.
For film the GN of a flashgun lowers for a ISO rating less that 100, and then, in manual setting, the distance and f# are determined - for that film speed.
This is exactly what I am doing for paper negatives. I 've assumed ISO6 for paper, therefore my flash's GN drops from 30 to 7.5.
At an aperture of f5.6 this gives a flash to subject distance of 1.34m. I set the speed to 1/60s and the lens on the X setting
Yet when I'm in the region of 1.5m to 2m from the subject I get a totally black image instead of an reasonably exposed image.
I'm obviously missing something and it is this I'm trying to determine.
Any and all help welcome
regards
Tony

[Randy]

Tony, this doesn't make sense to me, getting a completely black paper neg with the numbers you are giving just sounds to me that the problem lies somewhere other than what you have stated as the GN, flash distance, and aperture. It looks like your calculations are correct, which would indicate that the paper is or has been exposed to light at some other step in the process.

[JoeV]

Tony, there's little to no reciprocity failure with paper negatives. I don't understand the part where you say the guide number for film lowers for ISO below 100. The guide number is related to the flash output power. Are you implying your flash only indicates no lower than ISO 100? Then try extrapolation down to ISO 6 - what is it, 5 stops or so? Just assume the guide number stays constant and figure your exposure directly to your ISO. By assuming a lower guide number for sub-100 ISOs, you're effectively over-exposing.

[tonyowen]

Tony, I don't understand the part where you say the guide number for film lowers for ISO below 100. The guide number is related to the flash output power. Then try extrapolation down to ISO 6 - what is it, 5 stops or so? Just assume the guide number stays constant and figure your exposure directly to your ISO. By assuming a lower guide number for sub-100 ISOs, you're effectively over-exposing.

The dial/display on my flash guns shows if a film has a different ISO to 100 then the guide number increases/decreases proportionally. For instance, at ISO 100 (on one flash) I get the display of f2@15m (GN 30) if I change the dial/display to ISO 50 then I get the display of f2@7.5m (GN 15) Conversely if I go to ISO 400 the display shows f4@15 (GN 60). I'm assuming that the same changes also relate to paper negative. So for ISO6 the GN is 7.5 - which at f2 gives flash to subject distance of 3.75m. You are correct that the difference is 5 stops. Also it is all related the intensity of light decreasing by the square root of the increase in distance [decrease in ISO number). I just happen to prefer using a modified GN for calculations.

regards

Tont

[JoeV]

I confess I haven't done a lot of work with flash and paper negatives (but plenty with paper negatives in daylight). But here's a thought, crazy as it might sound.

The spectrum of light output by flash is probably a fairly narrow bandwidth of blue light, daylight balanced (the narrowness of bandwidth is an assumption, but sounds reasonable to me given how flash tubes work). The guide numbers are intended for panchromatic film, which are sensitive to a wide spectrum, from red to blue, but with flash-only illumination are only being lit by this narrow spectrum of blue light.

Now take the case of blue-sensitive-only paper being exposed by mainly blue flash. It's possible that its sensitivity would be similar to that of the blue spectrum of panchromatic film - ignoring the green/yellow/red end of panchromatic film's sensitivity.

Which implies you should try exposing the paper as if its ISO were similar to panchromatic film. Try ISO 100 to start, and go from there.

~Joe

[maltfalc]

I confess I haven't done a lot of work with flash and paper negatives (but plenty with paper negatives in daylight). But here's a thought, crazy as it might sound.

The spectrum of light output by flash is probably a fairly narrow bandwidth of blue light, daylight balanced (the narrowness of bandwidth is an assumption, but sounds reasonable to me given how flash tubes work). The guide numbers are intended for panchromatic film, which are sensitive to a wide spectrum, from red to blue, but with flash-only illumination are only being lit by this narrow spectrum of blue light.

Now take the case of blue-sensitive-only paper being exposed by mainly blue flash. It's possible that its sensitivity would be similar to that of the blue spectrum of panchromatic film - ignoring the green/yellow/red end of panchromatic film's sensitivity.

Which implies you should try exposing the paper as if its ISO were similar to panchromatic film. Try ISO 100 to start, and go from there.

~Joe

a flash is about as close to the spectrum of sunlight as you can get among light sources commonly used by photographers. i can't imagine how you came up with the idea that a flash puts out blue light when anyone who's seen one go off can tell it puts out white light.

[plaubel]

Recently I took a dummy and started with new to me paper negatives.
Please excuse the bad quality of my test prints:

[IanBarber]

When developing paper negatives in stray, are you developing by inspection under the safe light or are you developing to time?

I use Ilford MG developer diluted to 1:18 and I make up 300ml of total chemistry. I am scanning these and so far I have been snatching the negative from the developer when I think it looks right but not sure if this is the right approach.

I do find that they look low in contrast and not sure if thats to do with the way I am developing them or the fact that the developer may be going off. I only develop 1 or 2 at a time and then bottle the developer, remove the air and leave it until next time.

Any advice would be appreciated.

[Emil Schildt]

When developing paper negatives in stray, are you developing by inspection under the safe light or are you developing to time?

I use Ilford MG developer diluted to 1:18 and I make up 300ml of total chemistry. I am scanning these and so far I have been snatching the negative from the developer when I think it looks right but not sure if this is the right approach.

I do find that they look low in contrast and not sure if thats to do with the way I am developing them or the fact that the developer may be going off. I only develop 1 or 2 at a time and then bottle the developer, remove the air and leave it until next time.

Any advice would be appreciated.

I always develop by inspection - I use Tetenal Eukobrom 1:9 for most papers.
Whether the negative seems thin or not have two "solutions":

1: if looking thin, you can scan it and be surprised how much info you can get from it - but it can be difficult to use as a real negative.
2: "normal" looking is the opposite "problem"

If too thin, try to use a filter in front of the lens (ex multigrade filter 3) and remember to overexpose about 1 stop.

Hint: I have tried many types of papers (RC) for this, and in my experience FOMA rules that world - simply as it seems you can leave your paper for a longer time and thereby get a "deeper" development...

[IanBarber]

I always develop by inspection - I use Tetenal Eukobrom 1:9 for most papers.
Whether the negative seems thin or not have two "solutions":

1: if looking thin, you can scan it and be surprised how much info you can get from it - but it can be difficult to use as a real negative.
2: "normal" looking is the opposite "problem"

If too thin, try to use a filter in front of the lens (ex multigrade filter 3) and remember to overexpose about 1 stop.

Hint: I have tried many types of papers (RC) for this, and in my experience FOMA rules that world - simply as it seems you can leave your paper for a longer time and thereby get a "deeper" development...

Is the Foam paper single or multi-grade