Full spectrum bulbs for paper neg portrait?

[silversmith]

Hi,
I am trying to find out how the use of high output full spectrum or daylight bulbs (325watt and up) will affect the exposure times for shooting paper negative portraits.

I normally work outdoors with period cameras but have been asked by a museum to do a demonstration indoors this february. They want me to use paper negatives to keep costs down and I will be suffering from horrendous exposure times. I will be using ilford multigrade 4 and possibly harman direct positive.

Ideally I would like to keep exposure times under 30s. Has anyone tried using The Daylight bulbs in this way and if so what were the effects?

Your thoughts are much appreciated.

John

I am using a cycle poco no.5, 4x5, f7

[silversmith]

Hi again,
I might rephrase my question.
Can anyone tell me what would be the exposure time given by incident light from a studio light of x watts (1700 would be good). Using ISO 100 at f16, distance from subject 6feet?

It will give me a good idea of which lights to choose. I can do the maths from any given data. If you have any similar data it would be of help too.

Many thanks
John

[Doremus Scudder]

Since no one is answering, I'll take a shot...

First, with lights, the intensity of light on the subject will be dependent on the distance the light is from the subject, not just the "power" of the lamp (inverse square law and all that).

Short answer: You need to test.

First, use your light meter and your outdoor setup to find a working EI. Then, set up the lights at a comfortable distance from your subject (but close) and meter your subject using the same EI as a guide. Since you will be working with incandescents that have a different spectrum, and much less of the blue light your paper is sensitive to, you will need more exposure than outdoors (i.e., a lower EI). I would make test exposures one, two and three stops over.

Develop and see how you did. If the exposure times are too long, you can increase light intensity/speed by moving the lights closer to the subject, or simply adding more lights or wattage.

I am not sure how paper would respond to flash, but that might be an alternative light source that would get you both more intensity and more of the blue light you need.

Another possibility: try and find a window that allows you to use daylight...

Hope this helps,

Doremus Scudder

[silversmith]

Thanks for your reply Doremus. That's good information. The problem is that I don't have any lights to work out the calculations from. I have to choose wisely so I thought that I would try to work out some rough data before investing.

I have just ordered a couple of 105w daylight lamps (roughly equivalent to 525w incandescent) and will do some experiments with them based on your recommendations. I'll post the results on here when I have some.

Sadly the only flash I use is magnesium light for demonstrations and for this show I have been put in a particularly upmarket venue, albeit gas lit.


many thanks
John