Red filter compensation

[gmed]

Red filter requires a 3 stop compensation (factor 8). But to me, this is 2 stops too much. Using my meter, I only get one stop. Ive used 3 stop compensation when metering, and this totally over-exposed my photo.
I use the Expo dev app, and I usually put it on the Yellow filter instead of red.

What do you guys think about this?

Gevork

[E. von Hoegh]

Red filter requires a 3 stop compensation (factor 8). But to me, this is 2 stops too much. Using my meter, I only get one stop. Ive used 3 stop compensation when metering, and this totally over-exposed my photo.
I use the Expo dev app, and I usually put it on the Yellow filter instead of red.

What do you guys think about this?

Gevork

Three stops sounds about right (IIRC) for a red 29. Some films need more, some less. I'd go with what the film manufacturer reccomends for starters. You didn't say which film, or which red filter, r23, r25, or r29? It makes a difference. I'm not familiar with your app.

[vinny]

If it works, why the hell not.
Filter factors vary by film type, it's not cut n dry.

[gmed]

Sorry, its a red 25. HP5. Red 29 may need 3 stops, but 25A, 3 stop seems too much.

[Andrew O'Neill]

For me, a 1 2/3 stop increase is enough with the 25 and HP5. BUT, I increase development as there is some loss of contrast with this combination. It really depends on the film.

[cowanw]

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

[Drew Wiley]

Three stops is standard with 25 red and any typical pan film, including HP5. If you're using
a different factor, it's probably because your meter is reading things funny. 29 red is a
little different story because certain films, namely Fuji ACROS and Efke 25 are othopan
and can't take this degree of red without truncating shadow values. Then a few extended red films have been made, like Tech Pan. But otherwise, the performance of a 29 red is quite predictable, that is, per gray scale, though the presence of certain strong colors
in a scene might warrant creatively skewing this formula per "previsualization" (in case
you're an AA wannabee).

[gmed]

I dont think its reading funny things. I have a brand new Sekonic 758.
Ive read in other threads than red filter needs more like 1.5 stops, rather than the stated factor of 8 (3 stops).
My main subject is landscape. I use it to daken the sky. I have since switched to Tmax 100.
Mybe I should just meter through the filter, that way there is no guess work.

[Bob Salomon]

A filter factor is just a guide. Read through your meter and, if you like what you get, use it. But your final result will vary with exposure and development. So test and see what you like and then use it. Tailer the results to your liking. But a filter factor of 8 is the usual starting point. Heliopan states that if you are metering with a TTL system that you should set the exposure correction on the metering system to +1, except with Tech Pan film. They also state in their guide that the filter factor is "approximately 8x". Not that it is 8x.

[Steve Smith]

Mybe I should just meter through the filter, that way there is no guess work.

But there is more uncertainty as meters vary in the way they work through a coloured filter. Some are more sensitive to red than others.


Steve.

[gmed]

Thank you all.

[Drew Wiley]

To get an objective answer you need to start with something like a neutral gray card and
make a series of exposures using your preferred film and filter. Do not meter thru the filter.
Then read the resulting negatives with a densitometer and compare them to your normal
exposure value without any filter in place. This gives you your Zone V midpoint and how
filtration will affect it. Shadow values are a supplementary subject, and can be affected
by many things, including just how much blue light is in the shadows. At high altitude in
can be substantially more than at lower elevations, and require more compensation to the
red. TMax100 can render these deep shadows wonderfully, but if you overexpose, it will
be a lot harder to keep the highlights crisply separated. Believe me, I know this game.
With less contrasty lighting, or a film with a more gradual toe, you can get away with more.

[Heroique]

...At high altitude blue light can be substantially more than at lower elevations, and require more compensation to the red filter...

Here’s an example for this oft-overlooked situation.

If a shadowed scene at 500 feet w/ a red filter requires – let’s say – 2.5 stops of compensation, then a similar scene at 4,500 feet can reasonably require 3.5 or 4 stops, sometimes even more.

Yes, sounds funny, esp. if your (unfiltered) meter reads the two scenes identically.

Here’s why:

The high-altitude scene contains a higher proportion of blue light, the kind of light that a red filter takes away. This means that at 4,500 feet, the red filter is taking away a higher proportion of your total light – that is, less total light is reaching your film.

So you need more compensation at 4,500 feet, often significantly more.

But never mind all this. Just take notes. Examine your results. Adjust future shots to taste.

[Drew Wiley]

4500 ft?? That's LOW elevation. Try the color of light at 12000 ft. Oh yeah ... you guys
get more rain in the NW, so the sky is bluer due to the precipitation, so factor that little
dial or button on your light meter too. And while you're at it, note the pollen count and
how many campfires, forest fires, and jet contrails are in the vicinity, along any potential
reflections off approaching alien spacecraft. So when Bigfoot shows up, ask him to hold
his pose and say "cheese" a little longer, due to the slower red filter exposure, and hope
that he has a sense of humor.

[John Koehrer]

Best would be to test with different compensation values used. develop your film and choose the one you prefer.

As above this value can vary with different film. The meter does NOT likely have the same spectral sensitivity any of your films do.

[Heroique]

...When Bigfoot shows up, ask him to hold his pose and say “cheese” a little longer, due to the slower red filter exposure, and hope that he has a sense of humor.

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

BTW, 12,000 feet? I envy you Californians. Thanks to our heavy mountain snowfalls, it’s tough to get above 4,500 feet on wheels right now (forest roads), and here we are, mid-June!

[aporodagon]

Here's a test of filter factors and meters I posted a while ago. I think it gives an idea of how variable reading exposures through filters can be.

http://www.largeformatphotography.info/forum/showthread.php?45535-Metering-through-filters

[Corran]

My red filter calculations are usually in the neighborhood of 1 or 1.5 stops of adjustment.

Interesting idea about elevation. Where I live the highest hill is about 100ft above sea level...

[mdm]

Throw it away, its probably just red glass. I have a cheap set of ebay filters for a cokin p system that are completely useless, maybe made for dodgy digital people. Nothing like a proper filter.

[Corran]

Mine are Nikon and Hoya filters. 25A I should mention.

[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.

[John Koehrer]

[QUOTE=Heroique;902447]Thanks for the useful reference, Joseph.


For example, the Hutching’s Factor asks you to take a meter reading through the filter,

Reflected, not Incident if he meters through the filter.

[Brian Ellis]

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.JD

I didn't realize this table was in the book (which I don't own) but the same table/system was posted in View Camera magazine years ago. I used it with medium format film and an in-camera averaging meter (Pentax 67). It worked very well in that context. But I was never very certain about its use with a 1 degree spot meter since the through-the-filter reading with a spot meter depends on the tone of the area (presumably very small) being metered. So with a spot meter I just used the filter factor and that too worked well.

Absolute precision or perfection in exposure is unlikely to be achieved with any system when using a filter for b&w photography. Fortunately b&w film has plenty of latitude so small "errors" are almost always unimportant. I used to make two exposures of everything, one at the meter reading and the other at one more stop than the reading indicated. Invariably either would have given a perfectly acceptable negative so I stopped that practice.

[Lungeh]

Interesting discussion...
I had read, years ago, that there should be a one-stop difference with a 25a, and I used that ever since. Most of the time metering through the filter (on cameras with TTL) has borne that out. And my pictures usually look as I visualize, at least often enough...

Acros shot at 50, exact exposure unremembered (but I shot Velvia 50 at the same time--convenient for this method) in one of my secret places:78904

[Bill Burk]

But there is more uncertainty as meters vary in the way they work through a coloured filter. Some are more sensitive to red than others.


Steve.

And the Sekonic L758-DR responds to near infrared.

I was poking around with incident mode on my enlarger easel trying to get a 0 EV reading. Part of a sensitometry test. I had the ATN-Viper night vision scope on (preparing to expose a sheet of film)... I was shocked to see the reading jump... and was about to adjust the enlarger until I realized the ATN-Viper was aimed at it.

So you don't just take a meter reading through the filter. Because the meter is sensitive to light that the film isn't. You should give the film a little more light than the meter indicates.

[Bill Burk]

In Steve Simmons' 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

Gordon Hutchings explains the Filter Factors are needed because shadows are predominately blue light, which the red and orange filters cut severely...

[Andrew O'Neill]

Three stops is standard with 25 red and any typical pan film, including HP5.

I use several metres. Depends more on the film and less on the metre. The only film that I use that requires a full 3 stops compensation is TMY-2, but needs an increase of development time in zone system jargon, N+1.5. A very good article was written for PT magazine back in the 90's that dealt with this issue.

[Heroique]

Just a day in the field by a photographer whose field habits are his own, but which might be useful to others:

Shot 1 – Composition is half-sunlit, half shadows (i.e., both are important)

• No filtration
• Spot metering shows important shadows & highlights fall just within the needed zone limits
• No problem here

Shot 2 – Moments later, same composition, same light

• Now a red filter is attached
• 2 stops are added to compensate
• However, the red filter is actually “robbing” the shadows of a higher percentage of total light, since the shadows have more blue light than the sunlit areas.
• So the photographer adds an additional stop (a total of 3 stops) to save the shadows, understanding that this extra stop may push his highlights into a higher zone than he wants.

Shot 3 – Same composition, all shadows

• Red filter gets 3 stops (2 stops + 1 stop)
• No problem

Shot 4 – Same composition, all sunlit

• Red filter gets 2 stops
• No problem

Shot 5 – Same composition as Shot 3 (all shadows), but magically transported 10,000 feet higher where there is more blue light everywhere.

• Red filter gets 3.5 stops
• No problem

[kleinbatavia]

For a cokin red, I read 3.5 stops on my seconic meter. Generally go with three and it works fine.

[Drew Wiley]

With most films a 3 EV compensation works very predictably for a 25 Red in most lighting conditions. With some films a deeper 29 Red might need a bit more compensation. Never use a 29 filter for ACROS because it will simply lop off a zone or two. It's too far into the red for ACROS to respond to, since it is classified as an Orthopan film, not typical orthochromatic. I never meter through the filter itself. Filter factors work more reliably for me. And I have tons of experience withred filters on many kinds of film. Got a whole pile of TMY and ACROS shots taken thru red filters sitting on my work bench right now, waiting to be printed,
many taken at high altitude, various formats, 35mm, 120, 4x5, 8x10. Every single neg is perfectly exposed per filter requirements. But when in doubt concerning
an unfamiliar film, I run a bracketing test with 120 film and densitometer readings, before committing to serious shots.