Confirming Film Development Time using an 0.30 Neutral Density Filter

[Bill Burk]

I added a resource to describe a simple film test that can be done using an 0.30 neutral density filter.

Here is a link to the article:

Confirming_Development_Time

The way it works is that normal development is pretty close to a 50% gradient, and so if you bracket a couple shots. Give one normal exposure and give the bracketed shot 2 stops greater exposure, the difference should be close to 0.30

So after developing, if you lay an 0.30 neutral density filter on the normal exposed shot, it should look like the shot that received 2 stops greater exposure.

 

[pentaxuser]

Looks to be a good and simple test, Bill so thanks. I presume that the advice to take a picture of the 0.30 ND filter over the two negatives and then sharing it, simply serves to help you get others' opinions of whether the 2 match

If the user can judge this for himself as he really needs to be able to do then taking the picture to share it is of no real help or so it seems to me

What might be of more value and worth attaching to the article are examples of where the 2 do not match and then say what was needed in the form of more or less development in percentage terms to get to the match or is the use of say a certain percentage change in steps such as 5% or 10% just as good ?

Thanks

pentaxuser

 

[ic-racer]

Very clever Bill!

 

[snusmumriken]

Ingenious, very. Thanks for sharing.

 

[Bill Burk]

Looks to be a good and simple test, Bill so thanks. I presume that the advice to take a picture of the 0.30 ND filter over the two negatives and then sharing it, simply serves to help you get others' opinions of whether the 2 match

If the user can judge this for himself as he really needs to be able to do then taking the picture to share it is of no real help or so it seems to me

What might be of more value and worth attaching to the article are examples of where the 2 do not match and then say what was needed in the form of more or less development in percentage terms to get to the match or is the use of say a certain percentage change in steps such as 5% or 10% just as good ?

Thanks

pentaxuser

Thanks @pentaxuser

I agree it would help if I would show examples of underdevelopment and overdevelopment. I will improve the article with that.

Sharing the cellphone picture does give us a chance to help. But it also lets you play with settings to exaggerate the differences if they’re hard to see.

I used a tungsten light box to avoid fluorescent or LED flicker. (This is where having a half dozen light boxes comes in handy). A window would be a good choice.

 

[Sharktooth]

That looks like a great idea.

An alternative to the .3 neutral density filter, would be to use your developed film over the sensor of a hand held light meter. The difference between the two negatives should be one stop. The subject matter in your original negatives should be an even toned surface, such as a grey card or a large wall. That might be a more objective comparison.

 

[ags2mikon]

Thank you @Bill Burk. That is a very simple way to get you very close.

 

[Andrew O'Neill]

Clever! Thanks!

 

[Bill Burk]

That looks like a great idea.

An alternative to the .3 neutral density filter, would be to use your developed film over the sensor of a hand held light meter. The difference between the two negatives should be one stop. The subject matter in your original negatives should be an even toned surface, such as a grey card or a large wall. That might be a more objective comparison.

I’ve got plenty of gray background shots. To recognize them requires a bit of note-keeping.

I prefer recommending two shots, two f/stops apart because they stick out on the light table. Plus they are not a waste of film. Both shots could make an excellent print.

Time will tell if it is easy for people to get their hands on an 0.30 ND filter. I might start “accumulating” them so I can cut them up and mail out pieces to people who want to try it.

 

[ags2mikon]

Could you use Rosco cinegel ND.30? Now you could do ULF negatives.

 

[Bill Burk]

Credit to @dcy whose thread "A Lazy Man's Zone System" 09-JUN-2025 got me to thinking about the two-shot test. After I realized my post 10-JUN-2025 was really wrong, I had to address that by coming up with something that really worked.

 

[Bill Burk]

Could you use Rosco cinegel ND.30? Now you could do ULF negatives.

Rosco gel would be perfectly fine. Careful though, I've seen a lot of orange 85 + ND filters and those won't work.

 

[ags2mikon]

It is a lot cheaper than a Kodak #96 3x3.

 

[dcy]

The subject matter in your original negatives should be an even toned surface, such as a grey card or a large wall. That might be a more objective comparison.

I think this would work if I was a robot, but for a human, I think seeing an actual object or a pattern would work much better.

 

[dcy]

Credit to @dcy whose thread "A Lazy Man's Zone System" 09-JUN-2025 got me to thinking about the two-shot test. After I realized my post 10-JUN-2025 was really wrong, I had to address that by coming up with something that really worked.

Hey!

I am really glad that my thread inspired you. I think you came up with a brilliant test that
almost anyone can do.

Question: Suppose instead of a normal shot and one with a +2 EXP, I took one shoot with -2 EXP and one with +2 EXP. So now there's 4 stops difference. Could I then do the same test but with an ND4 filter instead of ND2? I'm thinking that with 4 stop difference you can detect smaller development errors.

 

[GregY]

Hey!

I am really glad that my thread inspired you. I think you came up with a brilliant test that
almost anyone can do.

Question: Suppose instead of a normal shot and one with a +2 EXP, I took one shoot with -2 EXP and one with +2 EXP. So now there's 4 stops difference. Could I then do the same test but with an ND4 filter instead of ND2? I'm thinking that with 4 stop difference you can detect smaller development errors.

before the advent of the internet the common advice was..... a good negative is one you can read a newspaper through..... . 2025....."what's a newspaper?"

 

[runswithsizzers]

I found a couple sellers on eBay (US), but I did not see that many Kodak ND 0.30 listed right now.

I ended up buying two, so if it works out I may have an extra for sale. I wish I thought to check for other brands, as I thought the Kodak ones are rather expensive.

 

[Bill Burk]

Hey!

I am really glad that my thread inspired you. I think you came up with a brilliant test that
almost anyone can do.

Question: Suppose instead of a normal shot and one with a +2 EXP, I took one shoot with -2 EXP and one with +2 EXP. So now there's 4 stops difference. Could I then do the same test but with an ND4 filter instead of ND2? I'm thinking that with 4 stop difference you can detect smaller development errors.

No, thank YOU.

You could do that. I'll try that out. I keep a stockpile of two-stop ND 0.60 filters because I like to put them on my enlarging lenses in the enlarger - giving me typical 32 second print exposure time. And as they get scratched, I like to replace them.

I'll try to under develop some film and see what the 2 stops difference test reveals, it might be good enough and has the advantage that you really don't waste any shots (because two stops overexposure is still a good negative).

 

[MattKing]

I think this would work if I was a robot, but for a human, I think seeing an actual object or a pattern would work much better.

Single colour mid-tone bath/hand towels work great for this. They offer even-ness of tone as well as observable texture, and are easy to handle.

 

[Bill Burk]

The densitometry and sensitometry behind the test.

In fact I did get 0.50 Contrast Index.

So the two negatives “should look the same” when an 0.30 neutral density filter is laid over the negative which received normal exposure.

Density readings of several rocks in the negatives show an average 0.27 density difference when I throw out a reading that wasn’t close. This is pretty close to expectations.

 

[ags2mikon]

@Bill Burk, are you reading the density through the .30 gel on your densitometer? If so could you just shoot a grey card?

 

[brbo]

If I'm reading this correctly, this only works for checking whether you developed the film to CI = 0.5?

Is 0.5 somethig like a gold standard?

I must admit that I've never in my life checked what CI film/developer manufacturer targeted with their suggested development times. So this method could easily suggest that something is wrong with my times, temperature, dillutions, etc. and/or would lead me to substantially different contrast index than what manufacturer had in mind when providing development times for different developers?

 

[Don_ih]

I think this would work if I was a robot, but for a human, I think seeing an actual object or a pattern would work much better.

the suggestion of a non-patterned surface was for his suggested alternative, which was

to use your developed film over the sensor of a hand held light meter

So a "robot" is what he had in mind.

 

[koraks]

If I'm reading this correctly, this only works for checking whether you developed the film to CI = 0.5?

Is 0.5 somethig like a gold standard?

That's what I noticed too, but I assumed that 0.5 would be close enough to 0.6-0.65 which would be a more common CI to aim for. And since this method based on a visual assessment would only be useful for spotting gross deviations, it wouldn't matter too much that the 0.5g-bar would be a little on the low side. The idea here is probably to see you're not hitting way too low or way too high, but somewhere in the ballpark.

 

[brbo]

Thanks @koraks! It was just to confirm that I understood the principle. For BW I'm basically "read the development times from the box/MDC and you'll always be good" kinda guy...

But I can see that this method can easily be applied to scanning with a lot more precision than in 100% analogue workflow visual inspection so @Bill Burk (or someone else) might expand on this article.