B&W filter exposure compensation.

[Cluster]

My last film to be developed had a few unexpected "features".
Aside from the faults that I introduced in my home processing (dust & water marks), I noticed that those shots that were made using a red or yellow filter tended to be underexposed, even using an auto exposure matrix metering system.
Those taken via a red filter are a little more underexposed than those via the yellow filter which are around 1 stop under. The shots that show this up well are those that have a large part of the frame covering a blue sky.
I recall reading some time ago that the auto exposure systems on most film cameras don't cope well with filters...
The camera I used for these shots is a Pentax MZ-5 set to matrix metering. It seems to work well on other scenes that are non-filtered.

Should I give a little more exposure than auto when using filters?

 

[dmb]

Which film? You could get really underexposed with red filter on ortho film. Some films like Fomopan are known as super-panchromatic and are extra sensitive to red and would get a bit overexposed with a red filter.

 

[Cluster]

Doh! Of course, it's about the film's sensitivity rather than a metering system... Thanks for the correction.
I'm using Fomapan 200 at the moment,( but have stock of Fomapan 100 and Kentmere100 also).

 

[Asha]

I use Foma 100 regularly in LF and have never experienced a problem compensating 1, 2 or 3 stops respectively for yellow, orange and red filters.

Bear in mind that I meter with a handheld lunasix meter or sekonic l308s so perhaps the matrix is getting itself in a muddle when filters are attached.

if the camera will allow, I would dissactivate all in camera metering and try using a seperate handheld device and compensate like I state above or by the recommendations of your filter manufacturer.

 

[StephenM]

I always use a Lunasix and apply filter factors. Built in meters can have spectral sensitivities that result in incorrect exposure with some filters. CdS cells are overly red sensitive, and therefore underexpose with red. The general advice is to accept the reading except for red filters, where you should add a stop.

 

[Cluster]

I will meter a scene with the filter off, then apply the regular filter factor. This way I might get more accurate exposures and learn what compensation to use with each film.

 

[StephenM]

Black and white filter compensation

Hi all, I've just bought some Cokin filters for black and white photography, a deep red (+3), orange (+1) and a yellow (+1/3). I naturally understand that as the filters are dark they'll effect the light entering to the film. As the filters say on them the plus numbers on them I'm guessing...

www.talkphotography.co.uk

 

[trypdal]

Some films like Fomopan are known as super-panchromatic and are extra sensitive to red

Not all of them though. Only the 400 extends a lot in the red. The 200 closely matches the spectral response of Kodak Trix

Foma 200 vs Kodak Trix

As for Foma 400 - It's like having an orange filter on at all times basically so I personally never shoot it with any other filters.

 

[Cluster]

Thanks for your help guys, there's a lot to take in. Thinking purely of the metering for a moment, I played with a red and a yellow filter on subject matter from an all blue sky to mix of trees, buildings and blue/white cloud sky.
My Pentax MZ-7 gave consistent filter factor changes as the filters were introduced and removed. 3 stops on red and 1 on yellow. I was surprised to find that my Pentax MZ-5 (they're very cheap, why not have both...) gave only 2.5 stops for the red and a half stop for the yellow. Surprising because I assumed that they would have the same metering (set to matrix on the MZ-5, it's fixed as matrix on the MZ-7).
Given that I have set the camera to ISO200 for the Fomapan 200, when I read in many places that it is around a half stop or more slower than the box speed and my dodgy metering, I could be around a stop or more underexposed. So maybe no mystery why my negs lack a bit of density on filters (although I'm happy with the box speed without filters).