Film speed test problem......!

[Matthew Rolfe]

I just undertook a film speed test and the density readings are a little strange. I took a meter reading from a 18% grey card in a shaded area in daylight, and then reduced the reduced the exposure by four stops to place it on Zone I (Ansel Adams test)

ISO 100 Adox CHS : Zone V 1/30 @ f11 - Zone I 1/30 @ f45

then I went up by one stop to test the film rated at 50 ISO 1/30 @ f32.....

I read the density of the 50 ISO and subtracted the FB+F to get the net density value, what is strange that It gave me a reading of 0.02. I had run the test a couple of weeks ago with the 100 rated at 50 giving the perfect Zone I density, but because I made a mistake with the developer I decided to do this retest. This is why the results are so strange. I have obviously made an error somehwere, but I can't figure out how?? I wasn't expecting too much of a difference between the original test and the re test but I decided to do it anyway so that I knew I had undertaken everything with the upmost accuracy. But now I'm back to square one as these results have come back so odd!

Any help would be greatly appreciated. Thanks

Wista Field 10x8 - Gossen Lunasix 3 - Schneider Symmar-s 240

 

[Anscojohn]

Just off the top of my head, I am not certain that exposure with a leaf shutter at the small apertures you use are strictly linear. I would suggest using larger apertures. Neutral density filtration might be needed.

 

[ic-racer]

In terms of leaf shutter efficiency, it will overexpose slightly at small apertures (but this is where you should test, unless you shoot wide open).
What do you mean by "went up" one stop. You should have "opened up" to lower number.
If you zero the densitometer on the B+F you don't have to worry about a math error.
I'd just repeat the test. If worried about expense of 8x10 sheets, you can cut it up and tape a little piece to a film holder.

 

[Matthew Rolfe]

I meant 'opened up'....increased the exposure by one stop.

Maybe I made a crucial error at some point but i honestly cant think where or when. As far as math is concerned I did zero on FB+F so I dont think the mistake happened there. It will just be one of those mysteries that will never get solved.

Retest I think.

Thankyou both.

 

[George Collier]

Exposing for the low (shadow) end can be tricky depending on the kind of shaded area you are in. EG open shade (illuminated by the sky, like the side of a building) and wooded shade, where the overhead may not be open to the sky.
Having said that, if I follow your exercise correctly, it really shouldn't have mattered if you were careful about what and where you took the readings, you are still placing a Z5 value down to Z1.
I guess I would say, starting over, I would use open shade, be sure it is a clear day, so clouds don't interfere, even though the exposure area isn't illuminated directly (it can still be affected), and make subsequent tests during the same time of day - the color temperature of the light can affect exposure due to differences in the spectral response of the meter and the film. Making all operating conditions the same is usually a good idea.