Colour analyser/spot meter as a densitometer ? - more trouble than it's worth ?

[nick mulder]

Hello,

I have a Colorstar 1000 colour analyser/densitometer/timer here that I'm going to use as a timer on/off switch for my UV bank. I thought with a little effort maybe it could be used as a black and white densitometer for large format contact print negs also, the light sensor has an 8mm diameter spot capture area.

So I figure if I zero it out/calibrate it somehow and place it over my negs (8x10" +) on a light box (the same light box and same area of the light box every time) then I should be able to read the suggested exposure times for a dense area and then do the same for the light areas, base + fog etc...

I'll have times, but with a little log2 calculation and comparison with some step wedge results I can get some more traditional numbers right ?

The sensor is made to work the other way around, as in projecting (enlarging) a (colour) neg onto it from above - maybe I'll pull it apart and make the profile around the sensor much smaller so I can be more sure I'm metering the part of the image I want to.

Would gelling the negs so I only use one colour be of assistance ?
I'll choose 'slide' mode over neg to avoid the orange cast compensation
I guess testing if the reciprocity compensation 'slope' mode vs. 'linear' will have to be tested with different mediums - Pt/Pd DOP vs. Pt/Pd POP vs. silver gelatin etc...

Or should I instead come up with a similar system with my spot meter ? - some kind of rig above the light box to keep variables to a minimum ?

Guess I'm just wondering who else is or has thought along these lines previously, any tips/suggestions ?

Nick M

 

[Mike Wilde]

I would give the manual a read, if you have one. My Colorstar 3000 (8 channel version) can go into b&w mode, and also can be used to measure density in logD, either as b&w or colour. You stick the sensor under/over a light source, zero it, then proceed to make film readings. You have the option to zero on fb+f if you are just interested in the logD density range.

I know the 2000 is reputed to be an easier to adjust timer with analyser, while the 3000 is an analyser with a less easily adjusted timer section. I never have seen a 1000 before, but it appears to be similar to a 2000. I think the slide setting just changes the slope of the analyser (twice as much filtration for a colour change in reversal printing than positive printing) and reverses the density to suggested nul display for time. I.e less time with more filtration, versus more time with more filtration between pos and neg. The orange cast of c-41 is adjusted for via the settings on the potentiometers, as far as I know.

I would consider using it in neg mode, with a continous white source to read a step, and then read the same sopt with a zero'ed UV source to try to get a handle on what the UV denisty of the film is, etc.

On my 3000 I believe in neg mode each step on the display is equal to 5cc of filtration.

If that holds true, it may help a bit better in calibrating this thing for you process.

Take care on how much inductive load you switch. These were probably not designed for much more that 500W.

 

[Mike Wilde]

Oh, don't worry about taking the sensor apart, just make a smaller hole aperture to fit over the larger one from the outside. Make it oversized, with cross hairs or concentric circles on the back side, and make a matching transperent target to aid in putting it over the right spot on the neg.