BTZS and new light souce

[mikepry]

I have been using a 400w metal halide light for all my alternative work until a friend gave me his homemade uv lightbox awhile back. It has the smaller diameter(8) 18" BL bulbs and is so much smaller and economical to use than the halide monster. I see many advantages to it's use over the halide.

So, having said that I'd like to switch over to it full time. Do I have to retest all my palladium developers with it(I use dichromate in the dev.)?

My standard print time was 10 minutes with the halide and it gave me 2 wedges on the step tablet pure black with a hint of lightening between step 2 and 3 and then progressive lightening on down the line with my developer that is in the middle as far as contrast goes.

When I used the UV unit at about 4" from the print frame, and the same developer I had 5 steps that merged as pure black before I started to see any differences between the steps. Can I just plot this on WinPlotter and go from there? OR......

Would you suggest increasing the distance from the light and getting only 2-3 steps black with my standard 10 min. printing time and then plot that? Does it affect my outcome by where the steps that start to show a difference fall on the test print from the step tablet for getting my ES data?

Thanks in advance!

 

[Michael Mutmansky]

Mike,

I would suggest you shorten the exposure time and come up with a new standard time.

There's no reason to increase the distance, in fact, I would probably recommend a shorter distance (probably about 3" if the lamps are spaced ideally) if I were setting up the unit myself. That won't change the exposure time much, but it may improve uniformity into the corners a bit.

It sounds like your base exposure needs to be about 4 minutes based on your description.

The outcome is affected by the last black point on the steptablet, because that reflects the density that will be printing maximum black on the negative as well, so you cannot make a shift to the new exposure unit without making a translation so that your times produce similar results.

Note also that you may notice a difference in contrast between the two uinits. It may be subtle, and essentially irrelevant, but it may be worth paying attention for as well.

Switching from a pseudo-point source or collimated source to a diffuse source will also produce a subtle difference in the look of the print as well, so there may be differences in apparent sharpness and microcontrast that you may notice as well.


---Michael