Film calibration question/Agitation problem?

[Peter Coats]

I want to ask if anyone might be able to explain some rather curious results I had whilst testing some TMX 100 - 120.

I am trying to determine my exposure index, and was shooting a grey card and placing it in various zones. One of the rolls I shot ended up having two different Zone I exposures - one was the first exposure, and the other was the 11th. Curiously, I got 2 very differrent densities, even though the f-stop and shutter speed were identical. The exposure 1 density was 0.16, while the exposure density was 0.09.

All I can think is that the two exposures received different "exposure" to the developer in the tank, since one was on the outer edge of the reel, and the other on the inner "core". Am I being too excessive with agitation? Whenever I process film with "normal" scenes instead of just grey cards I have never noticed any particular difference in densities from one end of the roll to the other.....was this just an anomaly?

Any input much appreciated,
peter

 

[df cardwell]

One of the problems of using the camera to determine Zone I response is that a small exposure error + small sensitometry error suggests a problem.

There is NOT much difference between .16 and .09, and this looks like normal shutter variation.

For film testing in a camera, why not look for a range of densities for each zone, rather than a point. In any case, you need a larger sample than 2 to nail down an accurate Zone I density when you're working with a shutter whose normal tolerance is +/- 1/2 stop.

This also assumes your densitometer is consistant.

As my old friend SK Grimes used to say, "Sometimes the Test tests the Tester".

 

[Saganich]

The variation could have resulted from any variable. Camera, developement, or light source. If your within a half stop of your targets then your OK. The true test is repeatability. I make zone I and VIII exposures periodically during normal shooting to see if all is on target. After a while the camera, exposure habits, developing habits, and printing habits all become normalized. And then its time to try something different :>)

chris

 

[RalphLambrecht]

The difference between 0.09 and 0.16 is about 1/2 stop. That is more than normal shutter variation, even for mechanical shutters. However, it could be acombination of shutter, aperture and agitation varation.

Which way is your emulsion side in the tank? To the outside or the inside of the tank?
How about light consistency between frame 1 and 11?

 

[Peter Coats]

Both exposures were made in identical lighting conditions, using a grey card on a copy stand. When I process, the emulsion side "faces in".....
I am testing a Mamiya 6. I've not had the shutter checked. I suppose I'll test another roll or two, and see what the results are.