TTL metering for black and white film with orange and red filters

ChrisR

ChrisR

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The manual for my Leitz CL says:

Through the lens metering generally allows for the filter factor. Films however differ in their spectral response; hence the readings may not be fully reliable with very dense filters. For instance, with an orange filter the exposure must be increased by one stop, with a red filter by about two stops. No precise values can be quoted, as the red-sensitivity of black and white films can vary appreciably.
Click to expand...

My question is: does this still apply with modern films? I'm using Tri-X, and sometimes use XP2 and FP4...
 
I think the spectral response of a film only applies when photographing ghosts.

In other words, dunno. I thought TTL was supposed to account for the filter factor but obviously it can't take the film into account. Personally I don't bother with filters on B&W, I adjust the contrast in LR instead. Does it make much of a difference which route you take?
 
I've never made any specific allowance when using orange filters on my MX, so I'm guessing it's possible to just ignore this (although I suppose it's possible the meter implementation might also make a difference, eg be less sensitive to red in the CL than the MX). With Tri-X I sometimes get the feel that one stop here, to stops there, who's gonna care. But I'd quite like to know... I've a feeling that words like panchromatic come into it!
 
I've used an orange filter with T-Max 400. Came out fine with no allowance.
 
Once used FP4 with both a dark red & a polarising filter on the lens as I wanted to turn the sky black. Can't remember what camera I used, but it was TTL metering & the exposure came out perfect.
 
It's still the case that modern films don't have a straight line spectral response. For Tri-X specifically, see here. I'm not familiar with the metering in a Leica CL; the older CdS cells were more red sensitive than the more modern silicon blue ones; this makes for a double hit - the film is less sensitive at the same place where the meter can peak in sensitivity.

I don't use TTL metering, so I rely on the filter factors (although when the light is more red (e.g. towards the end of day) the factor can be reduced slightly). The one thing to watch out for on a sunny day is that the shadows are illuminated by (blue) skylight, and the deeper the red filter the more proportionally the shadows will be held back and blocked. Moonlight effects are generally simulated by underexposing through a red filter.

The rule of thumb I've heard (with modern meters) is TTL is OK except for red, where you should add one stop.
 
Neopan and fomapan respond differently to a red, I've not read any data sheets, its just what I've noticed.
I shoot neopan and fp4 usually but I thought I'd try a bit of fomapan 100, I applied the same filter factor to it as I do the other two, the same scene with good exposure on neopan, was way under on fomapan, a good stop or so, so there must be some difference in their respective spectral sensitivities.
 
There is; you can find the data here for FP4 and Fomapan.

As you can see, Fomapan carries its red sensitivity a little further towards the IR than FP4 does, resulting in effectively a greater sensitivity at the red end. The Neopan curve isn't strictly comparable, because the other two curves are for tungsten light, and Neopan gives a daylight curve. The curve for Neopan shows a big difference in red sensitivity compared to the other two; plus it has a dip in sensitivity in the green region of the spectrum.

Filters of course have their own spectral curves...
 
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When I was given my Contax RTS II Quartz I took it out and used a RED filter and the shots were very under-exposed and I found out it was the metering sensitivity of the camera so you should do some tests, giving it MORE exposure for dark Orange and a Red filter.
 
StephenM said:
It's still the case that modern films don't have a straight line spectral response. For Tri-X specifically, see here. I'm not familiar with the metering in a Leica CL; the older CdS cells were more red sensitive than the more modern silicon blue ones; this makes for a double hit - the film is less sensitive at the same place where the meter can peak in sensitivity.

I don't use TTL metering, so I rely on the filter factors (although when the light is more red (e.g. towards the end of day) the factor can be reduced slightly). The one thing to watch out for on a sunny day is that the shadows are illuminated by (blue) skylight, and the deeper the red filter the more proportionally the shadows will be held back and blocked. Moonlight effects are generally simulated by underexposing through a red filter.

The rule of thumb I've heard (with modern meters) is TTL is OK except for red, where you should add one stop.
Click to expand...

pentaxpete said:
When I was given my Contax RTS II Quartz I took it out and used a RED filter and the shots were very under-exposed and I found out it was the metering sensitivity of the camera so you should do some tests, giving it MORE exposure for dark Orange and a Red filter.
Click to expand...

All very true.
Films
Filters and
TTL exposure sensors,
all have their own characteristics.
There was a very apparent change when the olds Cds meters were no longer made.
It has always been wise to make test shots for all your filters, This is true for both TTL and Independent hand held meters. This is one downside to being fickle and changing film types on a whim. For this and very many reasons it is far better to stick with just a few films and fully understand how they behave in exposure and processing.
 
I have to say I used a yellow filter on my Olympus trip 35 with I think neopan and I liked the results greatly really deep contrasts :-)
 
Thanks guys. The Leica advice suggested yellow filters allowed exposure as normal. I've been shooting for a year or two with an orange filter on the Pentax MX, which is about the same vintage as the Leica CL, no adjustment on the metering and it seemed to work well. The yellow filter I have on the CL doesn't feel strong enough for me. However, I've decided to get a 40.5 -- 49mm step up ring, so I can use all my Pentax filters, and that's on its way by slow boat from Hong Kong (can't complain at the price, free postage for £1.50 or so, but I ordered last month and the due date is March 20- April 5).
 
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