Confirming Film Development Time using an 0.30 Neutral Density Filter

Mr Bill · Jul 11, 2025

xkaes said:
While I don't disagree with this, given the prices for ND filters, of whatever type, you can probably find a decent, used, enlarging meter for less than a single ND filter -- and put it to other uses, to boot.

When I referred to some cheap ND filters I'm thinking of something like Rosco Cinegel. Unless I'm misreading online ads, looks like the cost of a 20x24 inch sheet is around $15 US, more or less. I would imagine that the quality would be perfectly suitable for visual estimates.

xkaes · Jul 11, 2025

snusmumriken said:
That’s absolutely true. The Ilford meter would lend itself admirably to the task. But you’d either want to use a diffuser, or photograph a subject a bit less coarsely textured than Bill’s pebbles. Matt’s towel suggestion, perhaps?

I've done similar, but more involved testing, with a Beseler Color Analyzer, and a gray card worked fine in my book.

xkaes · Jul 11, 2025

Mr Bill said:
When I referred to some cheap ND filters I'm thinking of something like Rosco Cinegel. Unless I'm misreading online ads, looks like the cost of a 20x24 inch sheet is around $15 US, more or less. I would imagine that the quality would be perfectly suitable for visual estimates.

I've seen lots of nice enlarger meters on EBAY -- Ilford, Beseler, Unicolor, etc. -- in the box, like new -- for less than that. And you get to use it in other ways. WIN-WIN.

It's your money, you decide.

Bill Burk · Jul 11, 2025

I've adopted a Beseler PM2M and picked up a handful of modules. Maybe I'll write up how to use it in the darkroom.

I use it for black and white printing, where I arbitrarily decided to use Yellow for Highlight, Magenta for Shadow and White for Density.
Can't use Cyan on my Omega D2 with Aristo Grid lamp (with teal light color) because it reads as if there's no light.

Mostly use it to dial in about a rough 30 seconds base exposure time.

Hoping to come up with something that can be free.

xkaes · Jul 11, 2025

Bill Burk said:
I use it for black and white printing, where I arbitrarily decided to use Yellow for Highlight, Magenta for Shadow and White for Density.

I have a PM2L, and this sounds like a sound approach.

Bill Burk · Jul 12, 2025

Still thinking of easier way to explain.

We all understand the best contrast for a black and white negative is half the contrast of reality.

Well, it's closer to 5/8 but easier to imagine half. We want a relatively low contrast negative to print on relatively high contrast paper.

That's the gist of it.

Going back to half. If you develop to half contrast of reality, then giving four times the exposure gives two times the density.

Now the pictures we take tend to have a good portion of their image detail in the straight-line portion of the film's "characteristic curve".

A picture taken with four times the exposure will have all the same relationships between light and dark, they will just be further up the straight line.

If we look at the negatives on a light table and block half the light from under the negative that received proper exposure, it should match a negative next to it that had four times the exposure on the same light table with all the light from the light table coming through.

That's where the 0.30 Neutral Density filter comes in. It blocks half the light.

0.40 Neutral Density filter, we've concluded with a little discussion, blocks the amount of light that would make the two negatives look the same at a higher contrast closer to ASA parameters.

Sound easier to grasp?

Alan Johnson · Jul 12, 2025

As was requested in post 2, can you explain how to tell from the phone pic if the film was over/under developed?

Bill Burk · Jul 12, 2025

Alan Johnson said:
As was requested in post 2, can you explain how to tell from the phone pic if the film was over/under developed?

PhotoShop a piece from one picture over the other. Kind of like a rangefinder patch. The difference should stand out. Or there’s no difference if you hit the contrast you were aiming for exactly.

If the difference is subtle you can increase contrast. Looking to see which is lighter or darker.

Alan Johnson · Jul 12, 2025

Take the case where the +2 stops negative looks darker, what does that signify?

Bill Burk · Jul 12, 2025

Alan Johnson said:
Take the case where the +2 stops negative looks darker, what does that signify?

It means contrast got away and run off with you. So develop less next time.

If it’s super dark then everyone will be able to tell but if it’s subtle then it’s a sign to just tweak your time.

Alan Johnson · Jul 12, 2025

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

boring old man · Jul 12, 2025

Bill, how does base+fogg effect this, it would seem the further from zone one, the less effect you will have?

Bill Burk · Jul 12, 2025

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

Hadn’t thought about it!

How about, I don’t know if it’s sticky enough, but…

2EZS as in Too Easy System and a mnemonic that you give additional two stops exposure to an occasional test shot.

Or maybe just 2EZ

Bill Burk · Jul 12, 2025

boring old man said:
Bill, how does base+fogg effect this, it would seem the further from zone one, the less effect you will have?

Cancels out, the difference is a density difference.

boring old man · Jul 12, 2025

Bill Burk said:
Cancels out, the difference is a density difference.

Yes, of course, never mind, senior moment.

Bill Burk · Jul 12, 2025

boring old man said:
Yes, of course, never mind, senior moment.

Believe me, it’s my senior moment that brought us here. I stupidly thought two normal negs would equal one that’s got two stops greater exposure but forgot the base plus fog and also neglected that we aren't starting at zero.

All this is just backpedaling

Bill Burk · Sunday at 11:24 AM

Banana for scale.

To interpret results, make a box open on top and bottom (cardboard will do) and put in a divider.

On one side create a slide that can close and open to adjust brightness.

Put the box on a light table with a piece of frosted glass on top. Paper will do.

Position the test pair on top and adjust until they seem to match.

When they do, see how much light you blocked with the slider.

Bill Burk · Sunday at 11:50 AM

If the slide blocks half the light or a little more when the two test shots are balanced, you’re good to go

Confirming Film Development Time using an 0.30 Neutral Density Filter

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