   |
Greetings All,
No surprise - again, I am confused!
Phil, I seem to have encountered a contradiction, or at least confusion, between the steps detailed in your article on determining personal speed point and the procedures we take during the 5 sheet film test process.
When we set out to do the normal BTZS film evaluation process, we make all the preliminary adjustments and then we make one test exposure to see if the exposure level is correct before exposing the 5 sheets with step tablet. For 100 ASA film, we aim for an EV level on the contact printing frame of approx. 4EV. The first test contact print of the step tablet is done at a "normal" time, say 7 or 8 minutes. This film is developed and fixed and inspected. Once washed, we make sure the film was properly exposed by making sure there are approximately 2 steps that are left virtually clear. If not, we adjust light level (height, f stop) and exposure duration in order to create an exposure that gives us approx. 2 blank steps. Once that EV level is established (whatever it may be), we run our routine 5 film sheet BTZS evaluation and stuff the data into Plotter. Plotter then finds the speed point and assigns whatever notional film speed we have entered to that speed point.
Where I get confused is when we go back and perform the testing you suggest in the personal speedpoint essay. There appears to be no "check" of under or over exposure in the procedure you describe. Simply returning to an EV of 4.0 for a 100 ASA film could well result in over/under exposure (at least the case for me since I had to back down to EV of 3 in order to obtain two clear steps). Should we be using the EV configuration that gave us the "2 clear steps" as the starting point that we then adjust around in order to get the ISO triangle speedpoint to move right or left to 2.4? Once one has further tweaked the EV level to the point where the ISO triangle speedpoint is 2.4 and the film still has 2 clear steps, do we then run the entire 5 sheet test again under this new exposure level?
This all seems a bit arbitrary - we know the initial speeds assigned by plotter could well be wrong, but aren't we creating some confusion by further adjusting exposure levels in ways inconsistent with the original film tests?
Perhaps I am far off in the weeds, but this issue seems pretty important since what plotter now generates is exported into the palm software and hence has bearing on every image exposure we make. If it does not have any bearing, then why do we undertake the exercise of tweaking the film test exposure to get to 2.4 speedpoint?
Thanks all for helping me sort this out!!
Regards,
Michael
|
|
|
|
|
|
|
