Confirming Film Development Time using an 0.30 Neutral Density Filter

@villagephotog Your understanding is correct and even sounds better than the best of my writing so far.

The reason I like bracketing a real shot versus shooting a gray wall is that it brings the waste of testing down.

As you echoed, it's not waste if you were going to take "that" shot anyway.

When you simply bracket a shot you took anyway, the waste is one shot.

I think of bracketing as wasteful. This disdain for the otherwise professional and good practice of bracketing carries over in my head from the days when I would take nature photographs backpacking on color slide film. I was younger and had to consider the money more carefully.

Bracketing turned a 36 exposure roll of film into 12 exposures. That immediately became a deal breaker to me.

But here we are talking about one extra shot every once in a while. Maybe once or twice on a roll. That doesn't cut your film supply very much at all.

Don_ih said:

I don't think it would be possible to make that any simpler than the one laser sold.

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The Kodak uses a gray plastic wheel that is likely faded or yellowed.

A densitometer that passes light through a sample spot in the middle of a field illuminated by the same light which took a longer path back to get there is simpler. I've got two of those: Look for "Marshall Studios Densitometer". There was one in the wild last year on Facebook marketplace.

snusmumriken said:

That’s certainly an interesting gadget (and it has a red dot!), but a good deal more complicated that what I was trying to describe. The comparator was essentially the same as Bill’s cardboard box, but being compact it focussed attention on the two samples being compared.

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Here's the direction I'm going. Using TeX to create a page to print with a checkerboard half.

Print and put on light box. Put hollow cardboard box with divider on that. And another piece of paper on that. This should cut one half by 50%.

The halftone pattern could be increased and decreased to cut light by any desired percent. I'll also provide a table of percent to density (know that 50% = 0.30) and a table of expected density difference per contrast index at two stops bracketing. Could even share the math so anyone who wants could pick any bracketing amount they're comfortable with (or if real world tests by students proves that two stops isn't enough to make the test results easy to read).

Alan Johnson said:

Thanks Bill, I hope to use this test.
Have you given it a name?

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The Two Stop Test

x Too Easy - rejected because I don't want to extend the "Zone System", "Beyond the Zone System", "Way Beyond Monochrome" naming convention.

x Two Shot - rejected because it doesn't tell you what the shots are.

Bill Burk said:

@villagephotog

The reason I like bracketing a real shot versus shooting a gray wall is that it brings the waste of testing down.

As you echoed, it's not waste if you were going to take "that" shot anyway.

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Yes, that's a cool benefit. I actually shot a real (i.e. not for testing) subject yesterday that would have been ideal for taking one extra +2 frame and reading it with my spot meter. And I am, in fact, trying to zero in a relatively new developer/film combo and a new process (rotary vs. inversion agitation). Wish I had read this thread first

What you can do with the spotmeter is verify the viewer. You can see when the darker half reads one stop less than the brighter half.

Bill Burk said:

What you can do with the spotmeter is verify the viewer. You can see when the darker half reads one stop less than the brighter half.

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Isn’t that going to be necessary for everyone, because printers and printer inks will vary? And if so, one could choose a bit of over-exposed film that happened to cut the light by 50%, perhaps?

snusmumriken said:

Isn’t that going to be necessary for everyone, because printers and printer inks will vary? And if so, one could choose a bit of over-exposed film that happened to cut the light by 50%, perhaps?

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That's why I'm avoiding gray. I think black checkerboard gives the best chance of being reproducible by anyone.

Could one use a slide copier attachment and the camera’s exposure meter to compare the two negatives, one after the other? Or would that not be accurate enough? I mean, it would probably be to the nearest 1/2 stop, whereas visual comparison should be a lot more discerning.

Bill Burk said:

That's why I'm avoiding gray. I think black checkerboard gives the best chance of being reproducible by anyone.

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I was wrong. Printed this out on laser printer and put on a light table and it did not cut the light 50%. Light came through the LaserJet ink.

Bill, just wanted to say thanks. I did not use your idea in its very cool true form -- i.e. I did not shoot an extra +2 exposure of a real subject that I was photographing anyway, and I did not evaluate the two negatives visually. But I did use the basic 2-shot idea yesterday.

I won't go into all the boring background (learning to use 4x5 film, a new developer, and a new processing method, and getting dull negatives), but I did a 2-shot bracket a la' your instructions yesterday, developed the film, and measured the difference with my spot meter. It was 9/10ths of an f-stop, which my (possibly faulty) math says would be a CI of .45 (with a margin of error for the meter, light panel etc., of course).

Now, I could tell just by looking at unbracketed exposures that I wasn't getting very much contrast, but still, it was cool to be able to put a reasonable number on the issue with a very quick and easy process. Much thanks!

villagephotog said:

Bill, just wanted to say thanks. I did not use your idea in its very cool true form -- i.e. I did not shoot an extra +2 exposure of a real subject that I was photographing anyway, and I did not evaluate the two negatives visually. But I did use the basic 2-shot idea yesterday.

I won't go into all the boring background (learning to use 4x5 film, a new developer, and a new processing method, and getting dull negatives), but I did a 2-shot bracket a la' your instructions yesterday, developed the film, and measured the difference with my spot meter. It was 9/10ths of an f-stop, which my (possibly faulty) math says would be a CI of .45 (with a margin of error for the meter, light panel etc., of course).

Now, I could tell just by looking at unbracketed exposures that I wasn't getting very much contrast, but still, it was cool to be able to put a reasonable number on the issue with a very quick and easy process. Much thanks!

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Thanks!

It certainly works the way you did it.

I like that you can run with the idea, and do what makes sense to you.