BTZS, pyrocat HD and UV readings

I have just done a series of BTZS testing of various films in Pyrocat HD. The purpose of this testing was to more accurately tune my negatives for the alt processes I do, as well as for Azo.

If I do a UV test (i.e. I read the test results with the UV channel of an Xrite 361), I presume that simply plotting this against UV readings of my step tablet will give me useful results? Or am I missing something here? I am confused because in a real life situation, I am aware that I will expose film with a more regular spectrum - why should I use the UV readings of the step tablet? Wouldn't it make more sense to use an ortho channel reading of the step tablet and simply plot the UV readings against those? Yes, I'm confused by this...

Secondly, if I am trying to produce negatives specifically for Azo using Pyrocat HD, if the spectral sensitivity of Azo closer to the ortho channel or the UV channel on my 361? Which readings should I use?

You dont need to plot the UV reading from the step tablet. For one, the UV and visible readings should be very close, about .01 to .02 units. If you are using the .1 over b+f film speed determination then this might represent a 10% error, but with the CI method is not an issue.

Second, you are exposing the paper to UV light, not the film. If you were using some kind of film that was UV sensitive and you needed to know the speed with UV exposure then you might want to plot the UV transmission of the step tablet, since all you need to know is the behavior of the developer and how it affects the film when it is exposed to normal daylight, you dont need to plot the UV readings.

In the end, since I had the same doubt I made curves both ways and saw no difference.....

Jorge said:

You dont need to plot the UV reading from the step tablet. For one, the UV and visible readings should be very close, about .01 to .02 units. If you are using the .1 over b+f film speed determination then this might represent a 10% error, but with the CI method is not an issue.

Second, you are exposing the paper to UV light, not the film. If you were using some kind of film that was UV sensitive and you needed to know the speed with UV exposure then you might want to plot the UV transmission of the step tablet, since all you need to know is the behavior of the developer and how it affects the film when it is exposed to normal daylight, you dont need to plot the UV readings.

In the end, since I had the same doubt I made curves both ways and saw no difference.....

Click to expand...

I agree with Jorge about this. A year or so ago there was a long thread on this very subject and I took the other position, i.e that it did matter to what type of light one exposed the film in testing. But alas, I now belive my position was wrong so I have to eat a little crow with this message.

But in this as in my other things we sometimes avoid paying for our mistakes because sometimes the things about which we obsess don't matter a bit. As Jorge remarks, if you do it both ways you get about the same result.

Sandy

Sandy

I popped out and bought a 47B as you suggested. The resulting plotter files lie midway between the UV and ortho readings - which is what my instinct was, but it's nice to get that confirmed when one is going to these lenghs!