I knew that a red filter darkens skies on black and white film. That was the limit of what I knew about colour filters before I sat down to do this experiment. I had a vague sense that yellow did something similar but less aggressive, and no real sense at all of what a green filter was for or why anyone would own one.
This is the writeup of three rolls’ worth of test frames (six on the Yashica 635, twelve in total across both rolls actually) shot on FP4 through red, yellow and green Rollei Bay I filters, alongside an unfiltered control frame. Three scenes, four frames each, twelve frames per roll. I came out the other end with a much clearer sense of which filter to reach for and when, and with a slight retraction of the dismissive position I took at the end of the video about green being pointless. Green is not pointless. I just was not photographing the right things to find out what it is good for.
How colour filters work in black and white
Black and white film records all visible wavelengths as shades of grey. The film cannot tell that a red apple is red and that the green leaves behind it are green. It just sees the total amount of light from each object, weighted by the spectral sensitivity of the emulsion, and renders both as some shade of grey. If the red apple and the green leaves reflect roughly the same amount of light in total, they will come out as almost the same grey. The picture goes flat.
A colour filter intervenes between the scene and the film. It passes light of its own colour and blocks light of the complementary colour. (Complementary colours sit opposite each other on the colour wheel: red opposite green, blue opposite orange, yellow opposite violet.) When you put a red filter on the lens, red light passes through almost unchanged, blue and green light is heavily blocked. The red apple still throws plenty of light onto the film and renders as a light grey. The green leaves now throw much less light onto the film and render as a dark grey. The picture has separation that was not there before.
This is the whole principle. Every colour filter does the same job. The variable is which colours it passes and which it blocks, and how aggressively.
The classic application is the sky. A blue sky throws blue light at the film. A red filter blocks most of that blue light. The sky renders as a dark grey (sometimes nearly black) and any white clouds (which throw a balanced mix of all wavelengths and are not really “coloured” at all) come through almost unfiltered as bright white. The result is the dramatic landscape look that defined Ansel Adams and a thousand imitators. Red filter, blue sky, white clouds, bright contrast.
But the same principle works for every colour relationship. A green filter darkens red flowers against green foliage. A yellow filter gently separates blues from yellows and greens. An orange filter sits between yellow and red in strength. Once you understand that filters block their complementary colour, everything else follows.
The Wratten numbering system
A quick aside on naming. The standard naming system for filters is the Wratten numbering system, originally developed by Frederick Wratten in the early twentieth century and adopted by Kodak as the industry standard. You will see filters labelled with numbers like #8, #15, #25 and so on. The system is not intuitive but the rough hierarchy is worth knowing:
- #8 is medium yellow (sometimes called K2). The classic mild contrast filter.
- #11 is yellow-green. Less common but useful for foliage work.
- #12 is deep yellow.
- #15 is deep yellow or orange-yellow. Slightly stronger than #8.
- #21 and #22 are orange filters of increasing strength.
- #25 is the standard red filter. The one most people mean when they say “red filter”.
- #29 is deep red. Almost into infrared territory at the edges.
- #58 is the standard green filter.
My Rollei Bay I filters are labelled by colour rather than by Wratten number but the densities map roughly to the standard system. The yellow is around a #8, the red is around a #25 and the green is around a #58.
The shoot
I picked three scenes that I thought would show different kinds of filter effect. The camera was the Yashica 635 with FP4 Plus loaded, giving twelve frames per roll. I shot four frames in each scene: no filter, then yellow, then green, then red. Same composition. Same exposure. The only variable was the filter.
I did not apply the filter factor correction for these test frames, partly because I wanted to see what the filters did to exposure as well as contrast, and partly because FP4 has enough latitude to absorb the underexposure that filters cause without losing the comparison. In real shooting you should always apply the correction. More on that below.
Scene 1 was the view down from the Church of St Arilda at Oldbury-on-Severn, looking out over the Severn estuary towards the Severn Bridge. The sky was reasonably clean with some scattered cloud, although the foreground was in shadow and the background was bright. A slightly difficult scene to test filters on because the contrast was already extreme between the foreground and the sky, but useful for seeing what the filters do to a complicated mid-range scene.
Scene 2 was a roadside cross I came across between Oldbury and home. A simple subject against a bright sky with bold white clouds, which is exactly the kind of scene the contrast filters are designed for. This was the scene where the filter effects showed up most clearly.
Scene 3 was four selfies, taken on a self-timer with the distance pre-measured because focusing on yourself with a manual focus TLR is not really possible. I wanted to see what the filters did to skin tones, which is the question Nick I never quite get a clear answer on from reading about filters.
What each filter actually did
Yellow gave the subtle effect I had been led to expect. The sky in scene 1 came out slightly darker than the unfiltered frame, with marginally more cloud definition. In scene 2 the sky was cleanly separated from the clouds, with the cross standing out crisply. The skin tones in scene 3 were warm and even, with the slight reddish flushing on my face rendered as a smooth mid-grey rather than as a blotchy pattern.
This last bit was the surprise. Yellow filters are routinely described as good for portraits, and the reason is exactly this. Human skin reflects a lot of red and orange wavelengths. A yellow filter passes those wavelengths almost untouched while blocking some of the blue light that creates the slight blue cast in shadowed areas of skin. The result is more even skin tones. I would not have known that without seeing it side by side.
The takeaway for yellow: it is the safe default filter for any black and white outdoor work. Slight sky contrast, slight separation of greens from blues, slightly warmer skin tones. Nothing dramatic but nothing wrong either. If you only own one colour filter, this is the one to own.
Red gave the dramatic effect I had been expecting. The sky in scene 2 came out nearly black, with the clouds standing out as bright white shapes against it and the cross rendered almost as a silhouette. The whole frame has that high-contrast slightly otherworldly look that you associate with serious landscape photography. It is really impressive when you see it on the same scene as the unfiltered frame.
The portrait, on the other hand, is genuinely disturbing. My skin came out as a pale washed-out grey with deep dark eyes. The red filter passes the red reflected from skin so freely that the skin renders as very light grey, while everything that is not red (including the pupils and the irises) renders darker. The effect is what I described in the video as looking like the squid out of Men in Black. Deeply unflattering. Almost ghoulish.
The takeaway for red: superb for dramatic landscape work with clouds. Avoid for anything with people in it unless you are deliberately going for the bleached-out alien look. A useful tool but a specialist one.
Green is the one I was wrong about in the video. I said it was good for nothing because I could not see what it had done in scenes 1 and 2 that yellow had not already done better, and I could see it making my portrait look slightly weird. That is fair as far as it goes but it misses the point of green filters.
Green filters are designed for scenes where green is the dominant colour, which is exactly the kind of scene I did not photograph for this test. Specifically:
The main use is foliage separation. A forest or a garden in the height of summer presents the camera with a wall of different greens. Blue-greens, yellow-greens, dark greens, light greens. To unfiltered black and white film, most of these greens render as similar shades of grey, and the picture collapses into mush. A green filter passes greens but slightly blocks reds and blues, which differentiates the various greens by their secondary colour content. Yellow-green foliage lightens, blue-green foliage darkens, and the picture has separation that simply was not there without the filter.
It also works for flowers against foliage. If you have a red flower against a background of green leaves, a green filter renders the red flower as a distinctly dark shape against a lighter green background, which gives the flower visual presence. Without the filter, the red and the green tend to come out as similar mid-greys and the flower disappears.
And there is a niche use for ocean against sky. A blue-green ocean lightens (because the green component passes through) while a blue-violet sky darkens (because the blue is partially blocked). The result is a clearly separated horizon line, which is otherwise difficult to achieve without filtration.
None of my three test scenes had any of these. The Severn estuary view had no real foliage. The cross was against sky with no green at all. The portraits had no foliage in the background. Of course the green filter did nothing useful. I was testing it in the wrong contexts.
If anyone reading this has shot a forest or a garden through a green filter and seen what it does, you will know what I mean. The green filter is not pointless. It is just situationally specific.
The orange filter I do not own
I do not have an orange filter in the kit, and I should. Orange sits between yellow and red in strength and is widely considered the best general-purpose contrast filter for landscape work. Yellow is sometimes too subtle. Red is sometimes too aggressive. Orange gives you most of the sky contrast and cloud separation that red gives you, with decent haze penetration as a bonus, without the dramatic blackness of the sky and the unflattering effect on skin tones. If you are starting from scratch and you have to choose between yellow, orange and red, plenty of landscape photographers would suggest skipping yellow and going straight to orange.
I will pick one up. Probably a #21 or a #22 in a Bay I mount to match the others.
Filter factors and exposure compensation
The other thing I did not properly cover in the video was filter factors. This is the practical bit that matters once you start shooting filters in actual conditions.
A colour filter blocks some of the light reaching the film, even after accounting for the colour selectivity. Less light means underexposure unless you compensate. The amount of compensation needed is called the filter factor, expressed either as a multiplier or in stops. Roughly:
- Yellow #8: filter factor 2x, which is 1 stop of compensation.
- Yellow-green #11: filter factor 4x, which is 2 stops.
- Orange #15 to #21: filter factor 2x to 4x, so 1 to 2 stops.
- Red #25: filter factor 8x, which is 3 stops.
- Deep red #29: filter factor 16x or more, which is 4 stops or more.
- Green #58: filter factor 6x, which is about 2.5 stops.
These numbers are approximate and will vary slightly between manufacturers. Always check the documentation that came with the filter, or do a quick test if you cannot find it.
The practical workflow is to meter the scene without the filter, then either open up the aperture or slow down the shutter by the number of stops the filter factor demands. So if your unfiltered reading is 1/125 at f/11 and you are using a red #25 filter, the corrected reading is 1/15 at f/11 (three stops slower) or 1/125 at f/4 (three stops wider). Choose whichever suits the scene.
Some people prefer to drop the ISO setting on the meter by the filter factor (so an ISO 125 film with a red #25 filter would be metered as ISO 15) which gives the same answer with less mental arithmetic. Either works.
TTL light meters that read through the lens will usually pick up some of the filter effect automatically, but they tend to underread on strong red and deep filters because the meter’s spectral response does not match the film’s. Most photographers I know apply the filter factor manually even with a TTL meter. It is more reliable.
What I have taken away
The experiment changed my view of all three filters.
Yellow is now my default for any outdoor B&W work. I had been treating it as a “lite” version of the red filter that I could not see a reason to bother with. It is not that. It is a genuinely versatile filter that does subtle work on skies and skin tones and gives a slightly better B&W frame in almost any condition. I should be using it all the time.
Red is for landscape work where I want the dramatic sky look. I will not be using it for portraits ever again unless I want my subject to look like a 1950s sci-fi villain.
Green I owe an apology to. The filter has genuine uses in foliage-heavy scenes and in compositions involving red and green elements together. I will test it properly the next time I am photographing a wood or a garden. The version of me at the end of the video who said it was good for nothing was wrong.
Orange I do not own and will rectify shortly.
The Wratten numbers are worth memorising. If you ever buy a filter second-hand and it is labelled with just a number, knowing that #8 is yellow and #25 is red will save you time. The filter factor matters in actual use and is worth writing on the case of each filter so you do not have to remember it.
The next outing on the channel was the Canon AE-1 Program review which has nothing to do with filters but is the next video in the playlist. After that there is a rather different sort of large format piece coming up.
If you have a green filter and you have used it on something that benefited from it, I would genuinely like to know. The comments on the video are open. So is the contact form on this site.