TUNGSTEN LIGHT & DIRECT POSITIVE PAPER??

[Joe Decko]

Quick question....

I just got a new pinhole camera (Ilford Obscura) and am using Ilford direct positive paper. I tried to take some shots in my studio using continuous tungsten lighting. I had a ton of issues in terms of exposure. I am guessing there is some sort of issue using tungsten lights with direct positive paper.

For my studio setup I started off using (1) 1K Arri fresnel. I was running a shutter of 5 minutes. I got nothing. I kept upping the exposure time until I was up to 20 minutes. At that time, I could get an image to register, but just barely. I added (2) more lights and it didn't seem to make much difference.

I tested the camera out the next day while outside and I got a great image after about 1:30.

With the amount of light I was using in the studio I could have fried an egg. There has to be a technical reason why the film was not reacting to very directional and intense tungsten lighting.

Any help would be greatly appreciated.

Thanks in advance.

JD

 

[grussmir]

Quick question....

I just got a new pinhole camera (Ilford Obscura) and am using Ilford direct positive paper. I tried to take some shots in my studio using continuous tungsten lighting. I had a ton of issues in terms of exposure. I am guessing there is some sort of issue using tungsten lights with direct positive paper.

Hm, paper negatives (and positive paper also) react higly to color temperature of light, since most papers are blue or (in case of multigrade paper) blue and green sensitive. Ilford DP is mainly blue sensitive, so check the spectrum of tungsten to see, that more than 90% of its energy go to non-blue spectrum (and heat...). Photographic paper will cutoff around 500nm (or 550 with multigrade) and tungsten lights have most energy at 700nm and longer... so now wonder.
The spektral line of Ilford Multigrade can be found here : http://www.ilfordphoto.com/webfiles/2011427105150454.pdf

And here's what a typical tungsten spectrum looks like http://zeiss-campus.magnet.fsu.edu/articles/lightsources/tungstenhalogen.html

Sun light has lots of blue (depending on the weather) and I always have to compensate for colortemp when pinholing...

 

[Joe Decko]

Thank you so much. That is really helpful. Two thumbs up for your sir