Red filter compensation

[mdm]

Well if they make the sky dark, they must be fine, but a filter is not always what a filter once was, in my experience.

[Corran]

Yes it darkens the sky.

These days I usually just meter through the filter, as my tested filter factor was exactly what the meter was giving me, taking into consideration the filter's effects (lower values on the blue, etc). I was also advised by a professor and well-known photographer that metering through the filter was what he does, and he is a master at the Zone System, so I'll take his word.

True though that there are many terrible cheap filters available on eBay and the like.

[Doremus Scudder]

Just a couple of comments on the above conversation:

First, I also advocate metering through a filter (I use a spot meter). However, given the different spectral characteristics of the meter sensor and the film, I find it useful to do a couple of tests to find a "fudge factor" for your meter-filter-film combination. It's pretty straightforward to do this and you only really need do it with the extremes; i.e., dark red, dark green, dark blue.

Another related consideration: It seems that some films change contrast a bit when exposed through one color of light. For example, I find that Tri-X 320 gains contrast when exposed through a deep red filter. That affects the way I develop.

So, for example, when I use a #25 filter, I automatically add 1 stop exposure (my meter fudge factor) from what the meter tells me and develop N-1 when shooting Tri-X 320. With T-Max 400, however, I have to develop more, not less, because T-Max seems to lose contrast when exposed through the red filter.

You can do your own tests to refine your system.

FWIW, the main advantage of spot-metering through filters for me is that I can see, in EV, what the contrast change for a particular area of the scene will be, which helps me better visualize the final print and choose filters.

Best,

Doremus

[Drew Wiley]

I was being a smart-ass, obviously. When I've been shooting in the NW myself, the sky has
almost always been gray! But my own custom is very simple. I use a 3EV factor for 25 red
regardless of location or pan film type. But in desert of mtn conditions I choose films with
a long stratight lline and excellent shadow separation: formerly Bergger 200, now more likely TMY400 for LF, Efke 25 for small cameras, or if I have long-scale films like ACROS or
FP4 I rate them down to 50 to push the shadows up the curve a little. I save films like
HP5 with its longer toe for more diffused lighting conditions. Here on the coast we often
get one kind of lighting part of the day, then much harsher light when the fog breaks up.
Somtimes I carry two types of film, but now that TMY is fine-grained, it's damn close to
an ideal multi-purpose LF film (that is, except for the price!).

[Andrew O'Neill]

It also depends on the subject. A red rose may need no compensation at all.

True, but only if you want black, empty shadows.

[E. von Hoegh]

Sounds like the age-old problem, How do you photograph a black cat in white snow?

Expose for the cat. Develop for the snow.

[cowanw]

"True, but only if you want black, empty shadows."

Just so, grasshopper.

[Joseph Dickerson]

In Steve Simmon's Using the View Camera there is a chart for filter compensation. The recommended procedure is to read/meter through the meter and then apply the suggested factor. For a 25A filter you read through the filter and then add two f/stops. This approach is attributed to Gordon Hutchings and it works for me. If you have the book, or your local library does, it's all on page 28.

Might be worth trying.

JD

[Heroique]

In Steve Simmon’s Using the View Camera there is a chart for filter compensation...

Thanks for the useful reference, Joseph.

It’s a procedure that works well for me too, especially for mountain-shadow detail.

According to the book, the reason to apply this “extra” factor is to help prevent under-exposed shadows. “Shadow areas,” it explains, “are primarily illuminated by blue light, and blue light is most severely curtailed by yellow, orange, and red filters.”

For example, the Hutching’s Factor asks you to take a meter reading through the filter, and then add an additional stop of exposure for filters #11 (light yellow-green), #16 (medium orange), and #21 (light red) and – as Joseph mentions above – to add an additional 2 stops for filters #25 (medium red) and #29 (deep red).

It recommends no additional exposure for yellow or medium yellow filters.

This extra factor is less important to me when few shadows fall on my composition, or if they’re unimportant.

[Corran]

Wouldn't that only be for an incident meter reading? If you use a spot meter you'd be placing the shadows in their proper place anyway, therefore accounting for the effects of the red filter, or so it seems to me.