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View Full Version : Correcting for film reciprocity failure, X-Ray Film results?



Randy Moe
22-Dec-2015, 15:34
I have not noticed anything here concerning X-Ray film reciprocity failure, and I post this here as techniques should be universal.

I am new at this and never used it, but last night I shot four 8X10 Ektascan X-Ray of Plastica using a single panel 3400K LED 'video' light at full power, which is bright. At 5 feet with gold reflector opposite my meter read, at nose ISO 80 1/8 f8.0. I needed a 2.3 bellows factor and shot the 4 images below. I didn't mark for order of exposure. Oops.

Exposure times and f stops are not in order.

2 seconds f9
8 seconds f16
32 seconds f32
8 minutes f90

All images as scanned in Vuescan, no corrections or PS except re-size for LFPF 750 pixel posterity.

I realize my technique is poor and found the below link.

http://home.earthlink.net/~kitathome/LunarLight/moonlight_gallery/technique/reciprocity.htm


#1 Has anybody made reciprocity tables for X-Ray? Where are they?
#2 Any advice on how to do this with better techniques without going insane. Oops too late there. :)

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Randy Moe
22-Dec-2015, 18:50
Talking to myself, what I see, is this film has no reciprocity failure to 30 minutes, under that lighting source, which is known to not be full spectrum.

I will be duplicating as much as possible under flash next week.

Or am I looking at this wrong, all exposures were nearly the same and time is not the issue in this set of negs.

I need to cut light and increase time, to see what reciprocity failure is.

Harold_4074
22-Dec-2015, 20:27
Randy,

In my limited experience, using the lens diaphragm to fine-tune exposure is a rather iffy business; a very small change in actual diaphragm makes a pretty big change in exposure for the smaller openings, and who knows how accurately the larger openings are marked? At the very least, you would want to make one series while closing the aperture in stages, and another while opening it from minimum (after removing backlash).

A near-point light source, if stable, moved away from a gray card in measured steps might give you a better experiment. Something non-lensed, like a small LED array, driven from a DC power supply should do the trick. Of course, a densitometer to read the film density would be ideal.

Randy Moe
22-Dec-2015, 21:13
Randy,

In my limited experience, using the lens diaphragm to fine-tune exposure is a rather iffy business; a very small change in actual diaphragm makes a pretty big change in exposure for the smaller openings, and who knows how accurately the larger openings are marked? At the very least, you would want to make one series while closing the aperture in stages, and another while opening it from minimum (after removing backlash).

A near-point light source, if stable, moved away from a gray card in measured steps might give you a better experiment. Something non-lensed, like a small LED array, driven from a DC power supply should do the trick. Of course, a densitometer to read the film density would be ideal.

Thanks Harold. I keep confusing myself. I now think a 32 minute exposure which has the same reciprocity as my 2 second exposure shows a neg of less than 1 stop density difference. And I then interpret that observation as no failure up to 30 minutes.

I found this which has very different results than my casual test. http://www.apug.org/forums/forum37/76797-x-ray-film-reciprocity-effect.html

I can improve the experiment, but my results show no need for that refinement. Any failure should have been grossly evident.

I assume no UV from this indoor LED 3400K studio panel. Kinda tosses a couple daylight exposure ideas right out.

Further testing is required.

Andrew O'Neill
22-Dec-2015, 22:47
I posted data years ago in the xray film comparison thread some where... It was for double-sided green latitude. I have used the data in the field for years.
I always conduct reciprocity tests under my enlarger. I use ND filters instead of adjusting the enlarger lens aperture. 31 step Stouffer step wedge in contact with the film. I expose one sheet, four times. 1/4, 1, 10, and 100 seconds. I use a piece of black paper to protect unexposed/exposed portions of the film. Densities are read, curves are drawn, data extracted. I like this method as only one sheet is required, and it's very accurate. This film has very poor reciprocity characteristics, but I love using it. I also have used Ektascan, but have not run this test. From my limited use, I suspect that reciprocity is slightly better, but not great. Apologies if my explanation isn't very clear...

Randy Moe
22-Dec-2015, 23:07
I posted data years ago in the xray film comparison thread some where... It was for double-sided green latitude. I have used the data in the field for years.
I always conduct reciprocity tests under my enlarger. I use ND filters instead of adjusting the enlarger lens aperture. 31 step Stouffer step wedge in contact with the film. I expose one sheet, four times. 1/4, 1, 10, and 100 seconds. I use a piece of black paper to protect unexposed/exposed portions of the film. Densities are read, curves are drawn, data extracted. I like this method as only one sheet is required, and it's very accurate. This film has very poor reciprocity characteristics, but I love using it. I also have used Ektascan, but have not run this test. From my limited use, I suspect that reciprocity is slightly better, but not great. Apologies if my explanation isn't very clear...

Thanks Andrew, I found your APUG post and chart, it is linked in Post 4.

I don't have enough ND filters to do it. I may try under enlarger with f stops.

Andrew O'Neill
22-Dec-2015, 23:37
Oh, that was linked to my data? ... I guess I should have clicked on it! The nice thing about ND filters is it rules out inaccurate f/stops. But go ahead and give it a shot.

Randy Moe
22-Dec-2015, 23:41
How do we know ND filters are accurate? :)

It seems to me my initial test has such a wide range of stops, failure should have been very obvious?


Oh, that was linked to my data? ... I guess I should have clicked on it! The nice thing about ND filters is it rules out inaccurate f/stops. But go ahead and give it a shot.

Andrew O'Neill
22-Dec-2015, 23:49
Well, apparently they can fade over time.... I did check them with my densitometre and they were bang on. I've had them for about 20 years.

Andrew O'Neill
22-Dec-2015, 23:50
You must be a night owl... Almost 11pm here. Must be in the wee hours of the am where you are.

Randy Moe
23-Dec-2015, 06:15
I sleep 4 and 4. Now back for the second 1/2.


You must be a night owl... Almost 11pm here. Must be in the wee hours of the am where you are.