Testing for film speed "focus at infinity"

[OMU]

This question may be asked before, but can't find the answer.

I'm trying to find my personal film speed E.I. for fomapan 200.
I have an Gandolfi 8x10 and an Nikkor-T ED 600 mm.

If I should focus at infinity, (as Ansel Adam writes) I'll have to place my grey card "in the neighbor's garden" and it will appears as a stamp on the film.

If I focus at infinity an fill the film whit the gray card, it's impossible to measure any different with the density meter.

Any suggestion?

[Goldman]

I shoot 4x5, but to find my film speed I put my grey card closer and focus. The gray card should fill up the screen. Than mesure and shoot. I am doing this for 30 years and I am happy with the result. (Even Ansel Adams can be wrong, Nobody is perfect!)

Bill

[Jim Noel]

This question may be asked before, but can't find the answer.

I'm trying to find my personal film speed E.I. for fomapan 200.
I have an Gandolfi 8x10 and an Nikkor-T ED 600 mm.

If I should focus at infinity, (as Ansel Adam writes) I'll have to place my grey card "in the neighbor's garden" and it will appears as a stamp on the film.

If I focus at infinity an fill the film whit the gray card, it's impossible to measure any different with the density meter.

Any suggestion?

The objective is to have the gray card out of focus so that texture does not enter the equation. Focus at infinity and then place the gray card in position to fill the frame.

[jp]

Focusing at infinity also removes the variable of compensation for bellows draw.

[OMU]

The objective is to have the gray card out of focus so that texture does not enter the equation. Focus at infinity and then place the gray card in position to fill the frame.

Have tried that, but the film get so even exposed that it's difficult to measure the different in densities in the different exposures.

[neil poulsen]

I focus right on my target, but make sure that it's evenly lit. Knowing the focal length of the lens and the distance to the target, I can calculate the bellows correction. I reverse correct the evaluated speed with this bellows correction.

[OMU]

I have done some test according to the advisees above, got my IE to 100 ASA. In Xtol 1:1 . Normal development time in a tray, it seems as 7:45 is about right time. 20 degrees C.

Neil, I would like to get your mathematic formula to calculate the bellow correction.

[ic-racer]

If you need to have the target in focus you could add this bellows factor calculator to the target and read the factor off your ground glass as you work.
http://www.southbristolviews.com/pic...ic/SBVCALC.pdf

[Jim Noel]

Have tried that, but the film get so even exposed that it's difficult to measure the different in densities in the different exposures.

Your exposures should be a third of a stop apart and easily distinguishable.

[Kevin Crisp]

I agree completely with Jim. Focus at infinity. Have the evenly colored/shaded card closer to fill the frame. It MUST be evenly illuminated. Check corners and sides with a spot meter to make sure they are the same.

If the exposures are 1/3d stop different, the density change should be obvious, particularly if you put the negative on a white sheet of paper, unless your development time is so far off you aren't getting any real density. The difference should really jump out at you if you put the negatives on a white sheet of paper.

If you are measuring with a densitometer and there is not a significant, orderly increase in density, something is wrong. You aren't exposing enough and/or developing enough. The shutter speed must be a known good one, and it is far better to change exposure by using the aperture than changing shutter speeds.