Macbeth TR927 UV readings

[UlbabraB]

Hi everyone,

I have access to an old Macbeth TR927 densitometer and I'm interested in its UV reading capabilities for my Pyrocat-MC developed negs for alt printing. It comes with a Macbeth calibration patch (which states 3.01 density) and the manual says that the procedure for calibration consists in zeroing all filters, then select the green filter, measure the calibration patch and adjust a knob in the rear to match the 3.01 density of the patch. I let the densitometer warm up about 15 minutes before the calibration. After the calibration, the UV reading of the calibration patch is 2.27. The manual doesn't says anything special about calibrating the UV channel.

I also have a calibrated Stouffer 21-steps tablet and I used it to check the reliability of the densitometer and found that the UV channel is reading much lower values in the high densitites than the blue channel:

stouffer blue UV

0,04 0,05 0,07
0,20 0,21 0,23
0,36 0,37 0,42
0,50 0,52 0,55
0,65 0,67 0,71
0,81 0,83 0,87
0,96 0,98 1,02
1,11 1,13 1,17
1,26 1,27 1,31
1,41 1,44 1,45
1,57 1,58 1,58
1,71 1,74 1,71
1,84 1,88 1,79
1,98 2,02 1,91
2,12 2,14 1,99
2,26 2,28 2,07
2,41 2,42 2,13
2,54 2,58 2,18
2,71 2,73 2,22
2,87 2,88 2,25
3,02 3,02 2,27

I also read several test films (Fomapan 100, Fomapan 200, Efke 25, Wephota 100, Kodak T-MAT Xray film, all developed with Pyrocat-MC) exposed with a EG&G sensitometer using the same steop tablet: while the Blue reading shows a nice pretty linear curve, the UV one is a big "S" with large amount of "highlight compression" much like the step table UV reading above.

Is that normal or the UV filter (or some other part) might have been deteriorated over time? Thanks!

[Bill Burk]

Hi Filippo,

I think it may be normal. A silver image, like your Stouffer scale, may dip in density in the UV.

This from Todd-Zakia Photographic Sensitometry under Density Measurements, Spectral Considerations: A silver image... is rarely strictly neutral... Even if the image is neutral, or nearly so in visible range, the absorbtion characteristics may change sharply in the ultraviolet...

The example graph shows a sharp drop from 350nm to 325nm where a patch that is 1.0 density in most of the visual spectrum falls to 0.05 in UV...

If you plan to expose your film in a sensitometer (doesn't matter if there is strong UV in your sensitometer, you only use it to expose film). and develop in Pyrocat... I'd recommend printing one of your own Pyro-stained step wedges next to the plain silver Stouffer step wedge.

Then see on the print whether the UV readings from your densitometer... are a fair predictor... of what actually prints.

Then you will know how good your densitometer is in the UV.

[sanking]

I have worked with two densitometers with UV reading capability, Gretag D200-II and X-Rite 361T, and many different Souffer step wedges. In the great majority of cases the Blue and UV readings of the Stouffer step wedges were almost identical, in a few cases the readings were different by a maximum of about log 0.20. But I never measured a Stouffer with either the X-Rite or Gretag that was off between Blue and UV as much as you record.

My opinion is that something is wrong either with your instrument or with the procedures.

Sandy

[UlbabraB]

Thank you for your help, now I'm pretty sure that there's something wrong with the UV channel/filter of the densitometer (mainly in the higher density values) since the Kallitypes I printed using these films (both test prints/step wedges and real prints) came out fine using small amounts of restrainer: 0-4 ml of dichromate solution, using sodium citrate developer and Bergger Cot320 paper.

I'm quite sure that the EI/developing times I empirically figured out in the past without the densitometer are right for my Kallitype printing procedure (the prints look fine, but mine are the only Kallitypes I ever seen in person :) ).
The availability of the densitometer seemed a chance to speed up new film types testing and to estimate the printing time and amount of restrainer needed for every negative before making the actual exposure/development, but I guess I'll stick to my human-eye procedure until I'll found a new working UV densitometer.