Question about determining min time to Dmax when film testing

[logan2z]

I've started to do some formal film testing to find my personal film speed and correct development time for Tri-X with my equipment/workflow. As part of that process, I made a test strip to determine the min time to Dmax with Ilford MG Classic Fiber.

Beyond the 10s mark on the test strip, I can see no perceptible difference between densities with my naked eye so I took 10s to be the min time to max black. But to be sure, I put the test strip on my lightbox and looked at it under a loupe. Doing that, I could see portions of the test strip beyond the 10s mark that showed small density differences. A similar thing happened when I made a test strip to see if a frame on my test roll at 4 stops under normal exposure would produce a density less than Dmax - I couldn't see any difference between the portion of the strip printed with the 4 under test frame and the portion at Dmax, but could when looking at the test strip on the lightbox and with a loupe.

My question is, is it best to simply go what with the naked eye sees when performing these tests since that's ultimately how a print will be viewed, or would it be better to hunt for density differences using visual aids like a loupe and a lightbox (or even a densitometer, which I don't have)? I don't want to compromise my results but I also don't want to get so anal that I'm looking for density differences that aren't perceptible to the naked eye.

 

[Andrew O'Neill]

There is nothing wrong with going with what you're eyes sees... This is coming from someone who spent years drawing curves with data from a densitometre. They do get you there faster, and pinpoint problems. You learn a lot more this way.

 

[pentaxuser]

My experience echos Andrew's in that any test strip viewed on a light box always shows the dark strips to be much lighter than using normal daylight. I'd go by eye and as you say this is how the final print will be viewed

pentaxuser

 

[logan2z]

Thanks for the input!

 

[albada]

Find the first two patches of your test strip that look identical under normal light.
Then illuminate them with an LED flashlight. Suddenly, the density-difference will be obvious.
That's because it is difficult for the human visual system to distinguish dark tones under normal lighting.
Lambrecht even has a table showing this phenomenon in his book, Way Beyond Monochrome (2nd ed). His conclusion is that one should printer lighter for a dark environment such as a hallway, and print darker for a bright environment. I suggest printing for the most common light-level in your home.

Mark Overton

 

[logan2z]

Find the first two patches of your test strip that look identical under normal light.
Then illuminate them with an LED flashlight. Suddenly, the density-difference will be obvious.
That's because it is difficult for the human visual system to distinguish dark tones under normal lighting.
Lambrecht even has a table showing this phenomenon in his book, Way Beyond Monochrome (2nd ed). His conclusion is that one should printer lighter for a dark environment such as a hallway, and print darker for a bright environment. I suggest printing for the most common light-level in your home.

Mark Overton

Makes sense, thanks.