FP4 Interpositive

I need to make an interpositive of a 4x5 FP4 negative; the positive will also be FP4. The interpositive will be the final product… The negative has a low density as the image is basically what looks like an acrylic rod with bubbles in it… I am planning on using my enlarger as the light source and contact print the neg in my vacuum contact easel. I am looking for some guidelines, rather a starting point for the exposure of the positive.

Any comments would be appreciated.

Chris

If your regular light meter has a right-angle incident head, I'd first de-focus the enlarger, and then set the aperture to give a workable exposure with the meter positioned flat on the contact frame's surface. I'd use that reading as the starting point, and then bracket around that reading. Based on your description of the original negative, some tesing may be required to arrive at an optimal density and contrast index in the positive copy.

Thanks for the feed back Ralph. I have the sekonic L-508 meter so this should work quite well. The negative is very dark as the object photographed was translucent and backlit. But what starting exposure.... Guess I defocus, back the light head off as much as possible and start at 15 sec. with a step wedge. As you can tell I have never contact printed a negative on to another negative

Depending on what you want the positive for, I would think you will have trouble getting enough contrast with FP4, particularly with regular film developer. On the rare occasion when I needed a b+w transparency from a negative, I contact-printed onto Ilford Line Film (no longer available, I think the Kodak equivalent still is) and developed it in Ilford Phenisol, which is a high-contrast (but not lith) developer (I think mainly intended for X-rays). Exposure-wise you can do a test strip (line film can be handled under bromide-paper safelight), I think my exposure was about 4 secs with the enlarger head up the top of the column and the lens closed 2 stops.

I think the FP4 positive will display a very definite bluish tint. If you intend to project the positive for viewing the tint might be objectionable.

I have made some nice interpositives using FP4 plus.

All this info is from memory but is pretty close to what I did.

As far as exposure...

I was using a color head projecting from 35mm to 4X5 using a rodagon 150, probably at about F11. I also had about 100CC of neutral density dialed into the head, I believe my exposures were about 2-4 seconds.

As Far as Development...

I processed using Ilfords DD-X developer at 75 degrees for proabably 10-12 minutes.

The 4X5 positives had decent contrast, while the original negatives were somewhat flat, so my development time may be longer than you might need.

If you need to increase contrast my approach was to decrease exposure slightly and increase development significantly... vice versa, to decrease contrast you would increase exposre and decrease development.

In my experiments I have found that you don't need much exposure, and when you have too much exposure it isn't always easy to tell in the dark areas... meaning try and expose for the highlights(the highlights in you final positive) and use your development to control the DMAX(the demax on your final positive)

Good Luck,

Corey