Red Filter exposure question

[zanzibarbungalow]

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Hey all,

I just ordered a red filter for my Summarit 5cm f/1.5 and am trying to figure out the exposure compensation needed. It's a Walz Coated Red Filter No 125. I tried Googling no. 125 but haven't really been able to find out how many stops I need to increase my exposure by. 

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I regularly use a B+W "090" red filter with my M6.  I would call it "red" as opposed to "light red", or "dark red", or "infrared".  Like Wratten 25 filter red, I suppose (maybe why Walz called it "125").  Even though the M6 meter looks through the filter, it needs an extra 1-1/3 stops to the ISO setting to obtain correct exposure.  If you're using a hand held meter, add three stops correction, as a starting point. There's no substitute for shooting some film and then seeing how it performs.

Also, you can hold your filter in front of your handheld reflected-light meter and compare the exposure to that same scene without the filter in place.

Good luck,

Edited July 14, 2021 by Danner

[zanzibarbungalow]

7 minutes ago, Danner said:

I regularly use a B+W "090" red filter with my M6.  I would call it "red" as opposed to "light red", or "dark red", or "infrared".  Like Wratten 25 filter red, I suppose (maybe why Walz called it "125").  Even though the M6 meter looks through the filter, it needs an extra 1-1/3 stops to the ISO setting to obtain correct exposure.  If you're using a hand held meter, add three stops correction, as a starting point. There's no substitute for shooting some film and then seeing how it performs.

Also, you can hold your filter in front of your handheld reflected-light meter and compare the exposure to that same scene without the filter in place.

Good luck,

Thanks! I was thinking that the 125 was just another name for 25. It definitely falls in between light and dark red. 

I generally sunny 16 it with my M3 but carry my Luna Pro from time to time to get things exact. Don't know why I didn't think to just put the dang thing in front of it though, doh.

[a.noctilux]

In my experience, obtaining "good exposure" with RED filter is tricky and would never be satisfying without some experimentations...

some rules of thumb to be aware of for b&w film:

- the main "color" of the subject (more or less red dominant ) a portrait in artificial reddish light or in sunlight would not need the same compensation

- landscape in winter or in autumn would not need the same compensation

- if with or without blue sky for example

- the famous "filter factor" must be seen as guide only

- even when metering from TTL or hand held meter, the meter's red sensitivity may not be the same as average color reading

- so experimentation with the film in use as also each film can behave differently

- I'd bracket largely, then choose later the "best frame"

 

edit ...

another thing that can be ennoying is focus shift for red filter ( when transmission in the lens not equal with all color ),

I have some Summarit 1.5/50, and not all have the "R" marking, one has the R on the dof scale at f/2.8 (between 1.5 and 4 markings for IR use)

...

Have fun ...

Edited July 14, 2021 by a.noctilux

[Danner]

I'll also toss this out there.  Try some Ilford SFX film, and have a go at some pseudo-infrared shooting.  I have been very pleased with this film on sunny days, and scenes with green foliage.  Striking, but not obviously infrared looking.

[spydrxx]

Over the years a factor of 3 has been a good starting point for me, but as suggested above you really need to experiment depending on the scene and lighting, film in use and your development to achieve the results you desire.

[pippy]

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3 hours ago, a.noctilux said:

...another thing that can be ennoying is focus shift for red filter...

Absolutely fundamental to understand this when using non-apo lenses.

My own '53 M-mount 50mm f1.5 Summarit does have the IR mark and, just in case it is any use to the OP (or anyone else), this mark is engraved between the f2 and f4 D-o-F indices on the RHS of the lens (looking from above) roughly 1/3rd of the way from the f2 mark.

Philip.

Edited July 14, 2021 by pippy

[zanzibarbungalow]

3 hours ago, Danner said:

I'll also toss this out there.  Try some Ilford SFX film, and have a go at some pseudo-infrared shooting.  I have been very pleased with this film on sunny days, and scenes with green foliage.  Striking, but not obviously infrared looking.

I actually have had some bulk loaded SFX film in my freezer for ages. No clue on the exp date so now may be the time to give it a go. 

 

Thanks everyone else, much appreciated. My Summarit has the R marking luckily so shouldn't be an issue. 

Edited July 14, 2021 by zanzibarbungalow

[Erato]

So-called "the missing manual"?

FYR. I hope that you would find what you looking for...Good luck.

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Edited July 14, 2021 by Erato

[a.noctilux]

Thanks Erato.

This manual confirms what I wrote as filter factors of "R2" are from 2 to 7 depending on lighting type, film in use, etc.

[giannis]

18 hours ago, zanzibarbungalow said:

Hey all,

I just ordered a red filter for my Summarit 5cm f/1.5 and am trying to figure out the exposure compensation needed. It's a Walz Coated Red Filter No 125. I tried Googling no. 125 but haven't really been able to find out how many stops I need to increase my exposure by. 

2 or 3 stops, depending on how light/dark it is. If you're using a film with increased red sensitivity (Rollei Retro 400/IR 400, Ilford SFX, etc etc.) start at 2 stops just in case.

If you have a portable lightmeter you can hold the filter in front of the metering cell, while pointing at something neutral under natural light (say a white wall) and see how many stops of light it steals. 

In theory, light meters can potentially be inaccurate when metering through a deep coloured filter cause their light response is not perfectly equal among colours. In practice, I've found light meters (integrated camera meters or handheld ones) to be very accurate with any filter that I throw at them, even including IR filters (720nm). So I wouldn't worry much about it.

Some things to keep in mind, are about your subjects. A red filter has a strong effect on faces (caucasian skin especially). So even though, say 2 stops is the correct correction factor for your filter, when shooting people you might want to use 1 to 1.5 stops instead less they end up looking like overexposed ghosts (unless that's the look you want to achieve). Similarly, when shooting a landscape with lots of greenery/foliage, you might want to give *more* light than the 2-3 stops recommended by the manufacturer, because greens darken with a red filter. And lastly, in tungsten light, again you might want to give less compensation than the 2-3 stops, because tungsten has a very strong red component so the filter actually blocks less light than when hit with natural white light.

In any case, I'd say trust your meter, and use some common sense when shooting people or heavily coloured/lit subjects, and you'll be fine.

 

I'm attaching some examples how skin can look with a 3-stop deep red filter and normal panchromatic film. It's HP5+, pushed one stop (to 800) in Xtol, so with the red filter accounted, exposure settings as if it were ISO100.

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P.S.: I missed @a.noctilux's excellent post. He described better and more concisely what I was trying to say. 

Edited July 15, 2021 by giannis

[zanzibarbungalow]

Thanks y'all. I've shot with filters a lot but appreciate the breakdown. This particular filter puzzled me with the lack of info out there but good to get a baseline. Experimentation is my mantra. 

Erato, thanks for finding that manual! 

Edited July 15, 2021 by zanzibarbungalow

[pippy]

14 minutes ago, giannis said:

...A red filter has a strong effect on faces (caucasian skin especially). So even though, say 2 stops is the correct correction factor for your filter, when shooting people you might want to use 1 to 1.5 stops instead less they end up looking like overexposed ghosts...

I'd add that when shooting b'n'w the best colour filter to use when the subject is people (again; caucasian especially) is either green or yellow-green. This has the effect of rendering the more reddish areas (lips etc) in a more natural fashion as these filters darken the areas resulting in a more realistic look.

Too dark a green, of course, will make them look more like a 'Goth'...

Philip.

Edited July 15, 2021 by pippy

[giannis]

21 minutes ago, pippy said:

yellow-green

Agree with that, basically a yellow-green (like Hoya GX0) is stuck on the front of my lens when shooting B&W: it barely steals any light (less than a stop) and gives a very natural look with subtle improvement both to skies/clouds and faces.

About green though, I'd tread carefully, especially with the ladies. Depends on your goal obviously. A green indeed emphasises freckles, pimples, imperfections, etc. as you said. It's great for a more "gritty" look, but usually (stereotypes and all, I know) that's desirable in a "manly" portrait, while for women it's more common that you try to "erase" such imperfections. In any case, a green filter will give a stronger, grittier look on a face, and a yellow/deep yellow will give a smoother, more flattering look. Of course you can choose the look you want for the situation regardless of gender and stereotypes.

 

And to keep it relevant, here's some TriX with a yellow filter.

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[Capuccino-Muffin]

Light yellow: 0.5 stop

Yellow, green: 1 stop

orange, dark green: 2 stops

red: 3 stops

deep red ala r72 or b+w 091/090: 5 stotps

[zanzibarbungalow]

I love this forum. Everyone's so helpful.

[Pyrogallol]

I have a bit of a collection of red filters of various densities and would agree that about three stops should be right with normal black and white film.

For Rollei 400 infrared I find five stops is about right for any density of red, from medium 25A to the very dense Leitz IR that you can’t see anything through.

[Narsuitus]

I routinely carry three color filters that I use when shooting black & white images on my Leica M6 and M10 (see filters in lower left corner). Some time ago, I tested my three filters and decided on the following exposure compensations:

Tiffen yellow: 1 stop

Vivitar orange: 2 stops

Tiffen red: 3 stops

 

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Hallo,

Look here: Leica M

[farnz]

A rough and ready way to find out of course is to meter the scene, remember the exposure, hold the red filter in front of the meter's input window, and then meter the scene again and you'll see how many stops the red filter introduces.

Pete.

[Ouroboros]

Three stops for a red filter (Wratten 25 or close equivalent as a rule of thumb), filter colours vary wildly between manufacturers.  There. is a lot more to black and white film photography than ‘rules of thumb’ if you want there to be! At least there is for me as I never use ‘sunny 16’ or meter through a filter. 
 
It begins with thinking about how I intend to process the film in accordance with it’s true speed, which is usually different to the box speed.  Prior experimentation helps. 

It takes a bit of time and effort but it’s worthwhile, especially with medium and large format photography.