question about stacking square filters

[ericantonio]

Hola! Happy 1 millionth day of quarantine.
I used to have yellow/green filters on my 35mm lenses. So I have a bunch of 49/52mm filters. Kinda hard to find yellow/green somewhere. Instead of finding filters to use for my Pentax 67, I figure I get the square ones so I can use them with my LF lenses as well.

I'm assuming I can stack a yellow and a green filter to make a "yellow/green" filter yes? It seems kinda obvious but hey, all this alone time is making me lose arguments with myself.

Also, what would be the approximate filter factor for that? Same as a yellow/green or add the yellow and add the green square filter together?

See, I'm losing an argument with myself already!

[Alan Gales]

You would add the filter factor of the yellow filter to the filter factor of the green filter.

I used to stack Cokin filters together back when I shot 35mm. The Cokin filter holder was made so you could easily do this.

[Mark Woods]

Meter a gray card through the filters to get your compensation. If you have a meter on the 67, put the filters on and meter through the lens. When I was shooting cinema, I stacked as many as 9 filters with no problems -- that said, one had to be careful about reflections.

[ericantonio]

You would add the filter factor of the yellow filter to the filter factor of the green filter.

I used to stack Cokin filters together back when I shot 35mm. The Cokin filter holder was made so you could easily do this.

That's what I thought, like "use your common sense man" but all this alone time is making me nuts. And I start questioning reality!

[ericantonio]

Meter a gray card through the filters to get your compensation. If you have a meter on the 67, put the filters on and meter through the lens. When I was shooting cinema, I stacked as many as 9 filters with no problems -- that said, one had to be careful about reflections.

Wow, great tip thank you!!! 9 filters. Dang man.

[Alan Gales]

That's what I thought, like "use your common sense man" but all this alone time is making me nuts. And I start questioning reality!

No worries. We were designed to be sociable creatures. Too much alone time will make anyone nuts. That's why solitary confinement in prison is such a punishment. :)

[Doremus Scudder]

When you stack colored filters, you just get the effect of the strongest filter. E.g., when you stack red and yellow, the yellow filter passes red orange and green; the red filter cuts out the orange and green, so you just get red. The yellow filter is doing nothing but degrading the image.

The same with yellow and green. Yellow passes red, orange and green, but the green filter only lets the green through, so, again, the yellow filter is doing nothing.

If you stack complementary colors, say green and red, you just get neutral density. If the filters are sharp cut and good quality, you'll get black...

Rule of Thumb: Don't stack colored filters.

A "yellow-green" filter is somewhere in strength (i.e., how much of the blue end of the spectrum gets eliminated) between yellow and green. If that's the filter you need, you just have to get one. You can't make one by stacking the stronger green filter together with the yellow.

Go to the Wikipedia site on Wratten numbers and familiarize yourself with the progression of colored filters from weaker to stronger (yellow - red) and the variations in between. Take a look at the color wheel and the concept of complementary colors as well and it will all become clear.

Best,

Doremus

[ericantonio]

When you stack colored filters, you just get the effect of the strongest filter. E.g., when you stack red and yellow, the yellow filter passes red orange and green; the red filter cuts out the orange and green, so you just get red. The yellow filter is doing nothing but degrading the image.

The same with yellow and green. Yellow passes red, orange and green, but the green filter only lets the green through, so, again, the yellow filter is doing nothing.

If you stack complementary colors, say green and red, you just get neutral density. If the filters are sharp cut and good quality, you'll get black...

Rule of Thumb: Don't stack colored filters.

A "yellow-green" filter is somewhere in strength (i.e., how much of the blue end of the spectrum gets eliminated) between yellow and green. If that's the filter you need, you just have to get one. You can't make one by stacking the stronger green filter together with the yellow.

Go to the Wikipedia site on Wratten numbers and familiarize yourself with the progression of colored filters from weaker to stronger (yellow - red) and the variations in between. Take a look at the color wheel and the concept of complementary colors as well and it will all become clear.

Best,

Doremus

Looks like I need to get some reading in today!! Thanks for the information.

[Dugan]

We won't worry about you until you start telling yourself jokes you've never heard before. :)

[LabRat]

With relatively mild color film filters, transmission readings can work, but for denser B/W filters, this changes... The optical density is different than the spectral sensitivity of the film... Then meters have differing color sensitivity across the reading spectrum... You can observe this by putting a strong colored filter on TTL metered cameras and notice the difference in reading and the listed filter factor... Then try it on a different TTL metered camera and you might see another change in reading... Then the pan film has its own sensitivity curve, and the overall dominant colors of the scene lighting change this too... And different color filters behave different...

You should try to not combine filters too much as each increases the air to glass # of surfaces affecting overall contrast and even internal reflections can ghost around some combinations... Combining color filters for B/W is not recommended or needed as there are single existing filters for not too much $$$... Usually multi filters are used with the appropriate color filter and some effect filter like ND, polarizing, soft filters etc...

For yellow/green, either darker yellow or lighter green have a similar effect without complicating the combined filter factor...

Also note that published filter factors are a starting point to be combined with film tests and the entire system...

Choose a couple of filters, know why you will use them, test, and be aware of conditions that will throw the exposure off...

Steve K

[TimHGuitar]

Yes. if you are using Wratten filters... don't stack them. The filters are very strong. But if you are using CC filters then you can stack them. CC filters come in different densities... .025, .05, .10, .20, .30, .40, and .50. None of these are as strong as a Wratten filter. CC filters are color correction filters and meant to be stacked.

[Mark Woods]

Having taught color theory at the American Film Institute Conservatory, I can accurately say that green and red are not complimentary colors. Green's complimentary is magenta, and red's complimentary is cyan. With that in mind, I would take the advice about stacking filters the same way I would about the statement of red and green being complimentary. All filters in the optical path will affect the quality of the light passing through them.

[Doremus Scudder]

Having taught color theory at the American Film Institute Conservatory, I can accurately say that green and red are not complimentary colors. Green's complementary is magenta, and red's complementary is cyan. With that in mind, I would take the advice about stacking filters the same way I would about the statement of red and green being complementary. All filters in the optical path will affect the quality of the light passing through them.

Mark,

Pardon my oversimplification (and resulting inaccuracy) for the purposes of simplicity and clarity; I didn't want to go into color theory in any depth since the OP needs to walk before he can run.

However, maybe we should give the OP (and anyone else interested) the basics:

Here's an easy way to think about it. The primary (single component) colors red, green and blue have complementary colors that consist of the other two components. For example, the complementary of red is blue-green or cyan. Extending this, we get the complementary of green, which is red-blue, or magenta and the complementary of blue, which is red-green, or yellow. (Note the use of the word, "complementary," not "complimentary," which means to augment or complete in this context. A primary and its complementary comprise all three of the primary colors.)

Seeing how yellow and blue are complementary is a bit counter-intuitive, since it's not so readily apparent that red and green together make yellow. They don't at all if you mix, say red and green paint (that's just an ugly brown...), but they do if you mix red and green light together. As a child I had a top that was colored with red and green stripes. When you spun it up, it was... yellow! I was fascinated by this phenomenon when I was young. Later, in optics and physics classes, we combined light of specific wavelengths by projection to see how the eye responded to them (the eye has rather wide-band receptors for red, green and blue that overlap in sensitivity). Red and green light projected together made a most vibrant yellow.

Back to filters: colored taking filters for black-and-white transmit their own color(s) and block the others. A yellow filter (we know from the above) transmits red and green and blocks blue. (This is an over-simplification, but will do for getting the general principles down.) That's why blue skies and other blue objects end up darker in a photo made with a yellow filter. A blue filter would do the opposite; passing blue and blocking red and green; blue skies would be lighter and red and green objects darker with a blue filter. Note that this filter pair is a primary color (blue) and its complementary, yellow (red-green). If we stacked a blue and a yellow filter together, the result would be the removal of all three primary colors, i.e., red, green and blue would all be removed... That's no light making it through to the film at all. Stacking filters of complementary colors always ends up removing all three primary colors, giving no light at all.

We can do the same with the other complementary pairs: A red filter (primary color) blocks cyan (blue-green). A photo made with a red filter darkens blue and green objects, such as the sky, green leaves, etc. and lightens red objects. Imagine a photo of a red rose make with a red filter; the flower itself would be rendered quite light, almost white, while the green leaves would be rendered almost black. The complementary filter to red, i.e., a cyan filter is less-often used, but is useful for blocking red and lightening blue and green objects. Interestingly, a cyan filter, when used with panchromatic film, will approximate the rendering of orthochromatic film, which is only sensitive to blue and green, not red.

On to green. A green filter blocks the other two primaries, red and blue, which together make the hue magenta. So when we use a green filter, red and blue objects will be rendered darker and green objects rendered lighter. Try the photo of the red rose with a green filter. Now you get lighter foliage and a very dark flower. Magenta filters are rarely, if ever used in black-and-white photography, but if they were, they would darken green and lighten the other two primary colors.

Thinking in terms of the three primary colors and their complementary colors helps us understand how filters work in black-and-white photography, but it, too, is an oversimplification for the purposes of understanding more easily. Keep in mind that their are a whole rainbow of colors between red and blue on the spectrum and that the human eye is a very complex organ in terms of spectral sensitivity, but with limits as well. In color photography, knowing more about saturation, hue, transmission spectra, crossover, etc., etc. becomes more important. Thankfully, we don't need to get into any of that to use black-and-white contrast filters effectively.

A quick note about CC filters. These are filters used primarily for color printing and balancing and come in different strengths. These filters can be stacked, as long as one stacks the same color, to get a stronger degree of filtration. For example, stacking two cyan filters of different strengths results in a filtration with the combined strengths of the two filters. Sometimes, we need to remove a bit of two of the primary colors from the mix in different proportions, so we can even stack two filters of different colors and strengths to do this. This type of filtration is useful in color printing and in color photography to get the right white balance to the print or the film. It is rarely necessary to be so subtle with black-and-white film.

Hope this helps,

Doremus