Using artificial (tungsten) light for your intial BTZS ( or other systems) testing

Cor · Feb 19, 2007

I have read the recent (sometimes heated) discussions on the BTZS and or the Zone system with great interest, learned quite a bit of it.

I do have one question about the initial testing for the BTZS: if I understand it correctly the first film tests are done by exposing a Stepwedge to 5 sheets of film with either an enlarger or a sensitometer. These devices have artificial light sources (tungsten or other).

How well does testing with these lights correlate with shooting outside under sun light (leaving out equipment influences such as flare etc. out of the equation).

The spectrum of a tungsten lamp is not the same as the sun (but the spectrum of the sun is not "stable" either)

Best,

Cor

David A. Goldfarb · Feb 19, 2007

With modern B&W panchromatic films, tungsten and daylight exposure should be pretty close, but if you want to be sure, then run some tests with the film you use. Photograph a gray card with tungsten, strobe, and daylight, making the exposure conditions as close as possible (same camera and lens, same shutter speed [you can't really control for this with strobes, but be sure with the ambient exposures your exposure is fairly short], same focus distance, process together or all on the same roll if you shoot rollfilm, etc.), then read the patches with a densitometer.

Roger Hicks · Feb 19, 2007

Filter the tungsten to daylight equivalence. Not exact, but a lot closer than most so-called 'tests'.

Cheers,

R.

sanking · Feb 19, 2007

Cor said:
I have read the recent (sometimes heated) discussions on the BTZS and or the Zone system with great interest, learned quite a bit of it.

I do have one question about the initial testing for the BTZS: if I understand it correctly the first film tests are done by exposing a Stepwedge to 5 sheets of film with either an enlarger or a sensitometer. These devices have artificial light sources (tungsten or other).

How well does testing with these lights correlate with shooting outside under sun light (leaving out equipment influences such as flare etc. out of the equation).

The spectrum of a tungsten lamp is not the same as the sun (but the spectrum of the sun is not "stable" either)

Best,

Cor

In practice there will be very little difference with most B&W films in your test results using a tungsten light or one balanced for daylight. However, I personally balance the tungsten light from the enlarger with an 80A blue filter. I also test with a Sensitometer that exposes the film with a daylight balanced pulsed Xenon flash.

Sandy King

Pinholemaster · Feb 19, 2007

I won't worry about it. Both are continuous spectrums, one is just a little more 'orange'.

jstraw · Feb 19, 2007

Do like me and use a Zone VI modified meter. That solves everything!

Christopher D. Keth · Feb 19, 2007

Get a couple of sheets of full CTB or an 81 on the camera and call it good. Either that or be satisfied that with modern films the difference should be small enough to be negligible.

Helen B · Feb 19, 2007

Christopher D. Keth said:
Get a couple of sheets of full CTB or an 81 on the camera and call it good. Either that or be satisfied that with modern films the difference should be small enough to be negligible.

I think that you mean an 80A, as suggested by Sandy. An 81 is a very mild warming filter (ie very pale salmon).

Best,
Helen

BarryWilkinson · Feb 19, 2007

I have considered building an exposure box using 5000K or full spectrum LED's. I would use a timer to adjust the exposure. Has anyone built anything like this?

Barry

donbga · Feb 19, 2007

sanking said:
In practice there will be very little difference with most B&W films in your test results using a tungsten light or one balanced for daylight. However, I personally balance the tungsten light from the enlarger with an 80A blue filter. I also test with a Sensitometer that exposes the film with a daylight balanced pulsed Xenon flash.

Sandy King

FWIW, Phil Davis told me not to worry about using an 80A filter for BTZS testing, though I beleive he does mention it in his book. So I didn't use one for my testing.

Where does one find a sensitometer at an affordable price?

BarryWilkinson · Feb 19, 2007

With reference to my previous post and Don's: -

I have a sensitometer. You can pick them up on the auction site in the US quite cheaply. I have a Xrite 383. Like most sensitometers I've seen, it has two exposure possibilities with Blue (460nm) & Green (510nm) light sources. The exposure time can be adjusted by switches. Herein lies a problem...

What colour source do you use to expose your film?
Not all films are particularly sensitive to these wavelength's. Notably J&C 400 Classic.

Also the exposure time settings are somewhat course (and unknown). I guess one could use ND filters?

Basically, the reason I considered making a LED sensitometer was to resolve these two issues. I decided that it would be difficult to use the Xrite to fine tune my BTZS PSP.

Am I missing something? Please note I am a complete beginner at this.

Barry

sanking · Feb 19, 2007

donbga said:
FWIW, Phil Davis told me not to worry about using an 80A filter for BTZS testing, though I beleive he does mention it in his book. So I didn't use one for my testing.

Where does one find a sensitometer at an affordable price?

Look in Printing and Grapics under Business and Industrial on Ebay. Sensitometers are also used in the medical field so you may also find them there.

One of the very best ones for photograhic purposes, often found for less than $100, is the EG&G Mark VII, or an earlier version Mark VI. If you look long enough one will probably show up. I have a Mark VII, but frankly it does not offer any signficant advantage over the the dedicated enlarger I use for BTZS exposures, where the light is controlled by a Metrolux II integrator.

Sandy

sanking · Feb 19, 2007

BarryWilkinson said:
With reference to my previous post and Don's: -

I have a sensitometer. You can pick them up on the auction site in the US quite cheaply. I have a Xrite 383. Like most sensitometers I've seen, it has two exposure possibilities with Blue (460nm) & Green (510nm) light sources. The exposure time can be adjusted by switches. Herein lies a problem...

What colour source do you use to expose your film?
Not all films are particularly sensitive to these wavelength's. Notably J&C 400 Classic.

Also the exposure time settings are somewhat course (and unknown). I guess one could use ND filters?

Basically, the reason I considered making a LED sensitometer was to resolve these two issues. I decided that it would be difficult to use the Xrite to fine tune my BTZS PSP.

Am I missing something? Please note I am a complete beginner at this.

Barry

I woud expose with the Green light. People who have done RGB color separations in camera know that the green filter negative looks the most normal of the three.

Sandy

Helen B · Feb 19, 2007

BarryWilkinson said:
With reference to my previous post and Don's: -

I have a sensitometer. You can pick them up on the auction site in the US quite cheaply. I have a Xrite 383. Like most sensitometers I've seen, it has two exposure possibilities with Blue (460nm) & Green (510nm) light sources. The exposure time can be adjusted by switches. Herein lies a problem...

What colour source do you use to expose your film?
Not all films are particularly sensitive to these wavelength's. Notably J&C 400 Classic.
...

I wonder how misleading wedge spectrograms are when they are made under tungsten light. They usually show the response at the blue end of the spectrum as being less than that at the red end - but that is because the relative exposure is less at that end, not because the film is less sensitive. If you look at Kodak's spectral response curves they look different from almost every other manufacturer's curves, because Kodak publish equal-energy curves, not tungsten wedge spectrograms.

Here is a comparison of the two methods for a particular film, which may resemble J and C Classic 400. The solid black line is the wedge spectrogram and the broken black line is the equal energy line.

Dead Link Removed

You can see that the film is more sensitive to blue light than to red light - and I should point out that the fall-off in sensitivity at the extreme blue end is probably exaggerated.

Best,
Helen

BarryWilkinson · Feb 20, 2007

Does indeed look similar to the J&C (Forte) data. Thank you Helen, now I understand.

Barry

sanking · Feb 20, 2007

Helen B said:
You can see that the film is more sensitive to blue light than to red light - and I should point out that the fall-off in sensitivity at the extreme blue end is probably exaggerated.

Best,
Helen

Perhaps a UV cut off filter was used? If not, I would have expected an increase in sensitivity toward the UV since most films are highly sensitive to light in the near UV.

Sandy King

Using artificial (tungsten) light for your intial BTZS ( or other systems) testing

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