Unicolor Subtractive calculator

[darkroom_rookie]

Is it possible to use this kit to calculate filtration for exposures longer than 48 seconds?

 

[Mike Wilde]

Most colour papers suffer a kind of reciprocity failure for times of longer than 25 seconds. I aim to keep exposures between 5 and 20 seconds when printing RA-4 by adjusting the lens aperture.

If you are plannign a big blow up, or are working from a dense overexposed negative, try balancing at a smaller print size, and then scale the exposure time up by the ratio of the proprtion of the square of any one image dimension to get the new exposure time.

You may then see a colour shift, and then have to dial in a filter and exposure time to compensate.

 

[darkroom_rookie]

OK, I'm a bit puzzled as to what to do with the result. This is a test print from a 7x enlargement of a color negative, exposed for 50 seconds at f8 with no filtration, diffused below the lens with the rectangular filter shown in the last picture. Which value from the red scale is the correct reading? The lightest one or the "medium value"?

 

[markbarendt]

I use a Besseler calculator and that one uses the lightest value, don't really know on yours.

 

[Mike Wilde]

A colour negative, though diffused, may still confuse the test rig if the negative in question does not integrate to neutral grey.
Photos exposed outdoors, with sky, and land typically do integrate to neutral grey.

I would presume if all tones integrate to give neutral grey, then the r, g and b rows would have the same intensity for the same time. Any discreprancy must then lie in the response of the paper.

So from your results I interpret you need more magenta (anti green) and quite a bit more yellow (anti-blue).

For me, filtrations with Kodak paper and Kodak or Agfa negs typically are in the range of 50M, 80Y. Fuji Reala is a totally different filtration for me.

To get more red, expose longer.
This rig might just give you balance, but the times on its edge suggest to me that the trial exposure should be 60 seconds, kind of like the Kodak print exposure guide.
Then with the 60 seonds trial exposure, balance the colours, and then read the time for unduffused exposure off for the tone of density you like.