Confirming Film Development Time using an 0.30 Neutral Density Filter

[boring old man]

1 and 2/3 stops should give you a slope of .6 with a .3 ND filter, if you want more contrast.

 

[Bill Burk]

1 and 2/3 stops should give you a slope of .6 with a .3 ND filter, if you want more contrast.

If it’s easy for you to dial in + 1 2/3 stops exposure compensation, that’s a very good idea.

 

[dcy]

If it’s easy for you to dial in + 1 2/3 stops exposure compensation, that’s a very good idea.

Well, as the person whose endless questions inspired you to develop your test, I would be remiss if I didn't mention that my camera has an exposure compensation dial with 1/3 stop increments. I can literally set the dial to EV = +1 2/3.

That's what inspired me to suggest 1/3 stop increments to dial in the gamma.

 

[Bill Burk]

Well, as the person whose endless questions inspired you to develop your test, I would be remiss if I didn't mention that my camera has an exposure compensation dial with 1/3 stop increments. I can literally set the dial to EV = +1 2/3.

That's what inspired me to suggest 1/3 stop increments to dial in the gamma.

Yup that’s fine for you. It will work on my Pentax ES-II in auto. But for any manual camera you might be dialing in differences of whole stops.

If I still go with two whole stops bracketing as originally planned, odd how graphically it looks close to being +0.1 density higher with +0.1 Log exposure increase. It’s not mathematically correct but might be close enough for practical checking.

Now it might be with an 0.40 neutral density filter on the light table, two stop bracketing might match.

I have an 0.10 Neutral Density filter I can add on the light table.

 

[xkaes]

Whether adjusting the EV or ISO scale to get 1/3 or 1/2 "f-stop" increments, the actual settings on the camera will vary from camera to camera -- and lens.

If you are using automatic exposure, there will be finer tuning than in manual exposure mode -- where you are using set shutter speeds (that can be "off"), and apertures than might have half stop settings (if you are lucky).

 

[dcy]

Whether adjusting the EV or ISO scale to get 1/3 or 1/2 "f-stop" increments, the actual settings on the camera will vary from camera to camera -- and lens.

Absolutely. But... Is that relevant to the test? ... Considering that we're trying to measure a slope, as long as the effect of the camera and lens is a systematic shift, the slope would be unaffected. The bigger concern is whether adding 1 stop in the camera actually adds 1 stop in exposure.

 

[Bill Burk]

I definitely think now that an 0.40 and an 0.30 ND filter will come in handy for the purpose, and that “two stop” bracket is best, something that can be done on any camera.

The prerequisites can be: obtain an 0.40 ND when you want to aim for the higher contrast associated with a diffuser enlarger and use 0.30 ND if you use a condenser enlarger or scanner.

 

[xkaes]

Absolutely. But... Is that relevant to the test? ... Considering that we're trying to measure a slope, as long as the effect of the camera and lens is a systematic shift, the slope would be unaffected. The bigger concern is whether adding 1 stop in the camera actually adds 1 stop in exposure.

That's my point. If you want to add 1 stop or 1.3 stops or 1.5 stops, how sure can you be that your camera did exactly that?

 

[Bill Burk]

If you use a sensitometer and densitometer and plot like I’ve been doing you can tell.

Cameras in automatic like dcy’s Pentax 17 and my Pentax ES-II will do well at giving the right exposure.

Electronic cameras in manual mode or better quality/better maintained mechanical cameras will do well to give the right exposure.

Older less trustworthy cameras might not be the best but maybe better to rely on f/stop changes instead of shutter speeds. Or maybe we add an 0.60 ND filter to the shopping list.

 

[Bill Burk]

We could probably do the whole Zone System thing here too.

 

[xkaes]

If you use a sensitometer and densitometer and plot like I’ve been doing you can tell.

I thought we were talking about a simple alternative to all that.

And, as I mentioned before, some cameras will do a better job than others at getting small exposure changes accurate -- others not so much.

 

[Bill Burk]

I thought we were talking about a simple alternative to all that.

And, as I mentioned before, some cameras will do a better job than others at getting small exposure changes accurate -- others not so much.

We are talking about doing this without densitometer and sensitometer.

But now that we're finding the comparison could be done with an 0.40 ND filter.

I have some clear Kodak TMAX400 (TMY2) 35mm film (e.g., from the beginning of a roll) that measures 0.20 density.

Two pieces of clear 35mm TMY2, could be used for the comparison.

Not 120 film, though because that film size normally does not incorporate permanent anti-halation gray dye in the base.

But many 35mm films have gray dye in the base, and we might be able to say: Do the test and put two pieces of clear film over the normally-exposed shot

 

[GregY]

I thought we were talking about a simple alternative to all that.

And, as I mentioned before, some cameras will do a better job than others at getting small exposure changes accurate -- others not so much.

........or you could just make a print....

 

[Bill Burk]

........or you could just make a print....

You could make two prints. One from the normal negative and then double the time on your enlarger and make another print. There should be no difference which will tell if you got the contrast right.

 

[boring old man]

Thinking about this, with a little mathematics, you could tailor this to any slope you need, for alt process, etc.

 

[Mr Bill]

I definitely think now that an 0.40 and an 0.30 ND filter will come in handy for the purpose, and that “two stop” bracket is best, something that can be done on any camera.

The prerequisites can be: obtain an 0.40 ND when you want to aim for the higher contrast associated with a diffuser enlarger and use 0.30 ND if you use a condenser enlarger or scanner.

Hi, I think it's a great idea to use a ND filter for comparitive visual viewing as a poor man's density comparator.

Regarding the test exposures, something I've occasionally suggested to curious friends is to take one shot with both a white card and 18% gray card in the frame. White paper, etc., comes in with a reflectance ~90%. So this gives an exposure change of about 5 to 1, roughly 2 1/3 f-stops difference in a single frame.

At the time, my thinking was to just take density reading. But Bill B's comparison method would probably work just fine here. Looking for, very roughly, a density difference of about 1.45 with film gamma, or whatever, of about 0.62 (roughly the film speed standard for b&w films.

I always figured that someone without a densitometer could use something like a commercial step wedge (say with 0.15 density steps) butted up against their film to estimate density. But if someone had some cheap ND filters (that they don't mind cutting up) they could probably stack a few up to get close to what they want.

Ps, for the uninitiated, density values sum together. So a stack of 4 pieces of 0.30 ND gives roughly 1.20 ND. Or 5 pieces gives roughly 1.50 ND.

Thanks to Bill Burk for the evaluation method.

 

[RalphLambrecht]

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.

I'm not getting it?

 

[koraks]

I'm not getting it?

I'll try to explain.

Imagine you expose a negative with just a single grey value, let's say it's a solid-colored wall with no texture and perfectly evenly lit. In the correctly exposed and developed negative its density comes out at 1.00logD. Now imagine that you expose another negative, immediately next to it, but this time you overexpose by 2 stops. What will the density of that negative be? If the gamma is exactly 0.5, then the overexposure of 2 stops would result in 2 * 0.5 = 1 stop additional density in the negative. 1 stop density = 0.3logD, so the density would become 1.3logD. Hence, if you observe the correctly exposed negative through a filter that adds 0.3logD density, then it should look the same (1.0+0.3=1.3logD) as the intentionally overexposed negative next to it.

That is, if everything worked out as planned and the development did indeed yield a gamma of approx. 0.5. If the gamma was much lower (underdevelopment), let's say 0.25, then the density on the overexposed negative would end up lower, at around 1.15logD. So it would look visibly lighter than the correctly exposed negative viewed through a 0.3logD filter. Conversely, if the gamma ended up higher (overdevelopment), let's say 1.0, the density on the overexposed negative would be higher (around 1.6logD) and the overexposed negative would look substantially darker than the correctly exposed negative viewed through the 0.3logD filter.

Hope this helps.

 

[FotoD]

I like your quick test, Bill. I will try a frame with +1.5 LV more exposure for a gamma of 0.66.

I'm thinking that a subject with tones mostly around zone 5 would give the most reliable results (it would stay within the straight-line portion of the curve).

 

[xkaes]

Hi, I think it's a great idea to use a ND filter for comparitive visual viewing as a poor man's density comparator.

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.

 

[Bill Burk]

We could catalog the ND gray antihalation of several common films and use them.

For example TMY2 is about 0.20 ND, so two pieces of TMY2 could be the trick that makes this accessible to more people

 

[Bill Burk]

@koraks that’s a good explanation.

 

[Bill Burk]

I always figured that someone without a densitometer could use something like a commercial step wedge (say with 0.15 density steps) butted up against their film to estimate density. But if someone had some cheap ND filters (that they don't mind cutting up) they could probably stack a few up to get close to what they want.

Hundreds of books have been written describing test methods that use hundreds of sheets of film, all to avoid spending six dollars on a Stouffer T2115 transmission step wedge.

I don’t know why.

But I have to accept not everyone has a Wratten No. 96 neutral density filter collection.

I’ve had both since I went to school. I use them all the time. But I also forget about them for long stretches too.

If only there were a common reference that everyone has - like a banana.

 

[snusmumriken]

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.

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?

 

[koraks]

@koraks that’s a good explanation.

Thanks for confirming; nothing as effective in understanding something as trying to explain it to someone else!