Contact Exposure of sheet film

[Mark_S]

I have a 4x5 negative which I would like to contact print onto another sheet of 4x5 film to get a transparancy. I'd like to use HP5+ film, which is fairly fast (box speed 400 ASA). I plan on using my enlarger as the light source.

To figure out the exposure of the contact print, can I just use a spot meter on the baseboard of the enlarger and place that in zone IX? Am I better off using an incident meter?

 

[cliveh]

I would have thought you are better off testing strips of film with incremental exposure changes.

 

[Whiteymorange]

I used to do this to get transparencies for printmaking. You may have a simpler way, but I have done it by working with an empty shutter on the lens board of a camera set up to look straight into the lit face of a lightbox. With my aperture wide open, I measured the actual opening and then the distance between that and the light box, divided and got the f-stop for the set-up. I took a meter reading off the lightbox, set my shutter speed and exposed a sheet that was behind a negative in a regular holder. Some holders are tighter than others. Luckily I had some that would readily accept two sheets. They are mounted face to face (emulsion to emulsion) and the resulting image will be right reading. I've done it with 4x5 and also with 8x10. Without a lens, your getting no image resolved on the film (yes, I know that the aperture is acting like a large pinhole and that it is forming an image of a sort, but the focal length for a 1"pinhole is way longer than the distance to your film, so you'll never notice it). It worked like a charm. YRMV, of course, and you may have a different idea for your light source. I had a large, clean lightbox and the blank glow was easy to work with.

 

[Kawaiithulhu]

A perfectly focused image of a lightbox is still just a flat light, I think you're ok here with the in-camera idea

I may try this this weekend, it sounds like a fun twist that I hadn't thought of before!

 

[ic-racer]

You need to use a film-plane light meter. Horseman used to make one. There were others also.

 

[Jim Jones]

Exposure when projecting with an enlarger is fairly similar to the exposure when contacting with the same enlarger setup (less negative) as a light source. Therefore, measuring or guessing at the exposure, and changing it in proportion to the sensitivity of the film will give accurate enough exposure for the first test shot. Another technique for making transparencies is to shoot them in a macro camera. Exposure is calculated much like any other macro shot. One problem with making B&W transparencies: most film yields low contrast transparencies. Tech Pan developed in print developer was an exception. I haven't tried any current high contrast films. Extended development of normal films may boost contrast to practical levels, but I haven't had to try this.