UlbabraB
15-Dec-2012, 09:00
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!
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!