Film Speed and Development Test (Excel spreadsheet supplied)

[CPorter]

Make sure your tape lets negligible light through.

Since chemical fog is the density increment on the film base due to processing, it should be measured without any density added from light exposure, so can't agree with you on that one.

I should have clarified, I was looking at Ralph's spead sheet from his website, I'm sure there's an explanation that I'm not aware of.

[PeterB]

I thought you were using the tape to block the light. If so then why don't you agree it must let negligible light through?
Why don't you just use the film's leader or trailer or inter frame spaces to measure the B+F ?

[PeterB]

Been looking at the spread sheet, the 21st or 31st step is shown as being the chemical fog density, but these are defined steps and clearly, at least from my tests, contain density both from exposure and chemical fog.

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It depends entirely on the amount of exposure you give during your test as to whether step 31 on the tablet contributes to exposure or not. Ralph's spreadsheet actually relies on there being no exposure for at least the last step, otherwise it can't work out the base+fog density which is critical for its calculations.

[CPorter]

I thought you were using the tape to block the light. If so then why don't you agree it must let negligible light through?
Why don't you just use the film's leader or trailer or inter frame spaces to measure the B+F ?

It's a 4x5 step tablet, sorry I didn't make that clear---the tape just provides a larger area by which to read just fog density.

[CPorter]

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It depends entirely on the amount of exposure you give during your test as to whether step 31 on the tablet contributes to exposure or not. Ralph's spreadsheet actually relies on there being no exposure for at least the last step, otherwise it can't work out the base+fog density which is critical for its calculations.

My test procedure is here, which is definitely different than what is explained in Ralph's method, but my resulting negatives are hard for me to argue with, and results are what matters------but I've been thinking on his method and feel like it is something I might try, could easily do it in a mornings worth of time when the darkroom is functional.

[RalphLambrecht]

I thought you were using the tape to block the light. If so then why don't you agree it must let negligible light through?
Why don't you just use the film's leader or trailer or inter frame spaces to measure the B+F ?

Exactlyexactly!!!

[Stephen Benskin]

Hey Ralph, welcome back.

[CPorter]

Exactlyexactly!!!

come on, why should it let neglible light through, sounds like you are agreeing that where I want to read just fog must also have density from light.

[RalphLambrecht]

come on, why should it let neglible light through, sounds like you are agreeing that where I want to read just fog must also have density from light.

yes, i do!

[PeterB]

Originally Posted by CPorter
come on, why should it let neglible light through, sounds like you are agreeing that where I want to read just fog must also have density from light.

come on, why should it let neglible light through, sounds like you are agreeing that where I want to read just fog must also have density from light.

yes, i do!

NO !!! The black tape used by CPorter as a mask should NOT let any light through. When I used the word negligible I intended it to mean "a sufficiently small amount (of light) that will not contribute to any measurable increase in density". Letting light through the tape that contributes to a density increase is contrary to the intention of using the black tape in the first place !!