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Red Green and Blue colour separation filters...


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#1 Richard Tuohy

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Posted 21 January 2006 - 01:45 AM

I am interested in tripple exposing colour reversal film through Red Gree and Blue filters respectively. This if for an experimental film and I don't need or expect 'true colour' as a result - but something sometimes close would be desirable.
Anyone know if it is possible to get a set of filters designed to work together in this way? Surely technicolour cameras used some technique like this combined with semi-silvered mirrors. Certainly I can purchase red, green and blue looking filters and see what I get, but the respective intensities of the three colour filters would greatly effect the composite colour. Are there such things as 'colour separation filters'?
Any thoughts would be appreciated.
Regards,
Ricahrd Tuohy
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#2 Jamie Metzger

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Posted 21 January 2006 - 03:08 AM

I am interested in tripple exposing colour reversal film through Red Gree and Blue filters respectively. This if for an experimental film and I don't need or expect 'true colour' as a result - but something sometimes close would be desirable.
Anyone know if it is possible to get a set of filters designed to work together in this way? Surely technicolour cameras used some technique like this combined with semi-silvered mirrors. Certainly I can purchase red, green and blue looking filters and see what I get, but the respective intensities of the three colour filters would greatly effect the composite colour. Are there such things as 'colour separation filters'?
Any thoughts would be appreciated.
Regards,
Ricahrd Tuohy



I'm only offering my insight from learning this process from a 35mm still project. I think you need the same amount of transmission from each of the filters, and you should be fine. You need to experiment though.

I've seen a guy take 2 second exposures with red, then green then blue (in no particular order), while triple exposing, and you get a quite unreal effect. It's nice, but he was showing me a sample pic of ocean water, so I don't know how anything else would look.

One thing that did cross my mind is the way that RGB agitate the emulsion; how blue is on top, then green and then red; there might be a certain order in which filters to use, but I can't help you with that.

If you can, post some images of your test when you try it. I'd like to see how it comes out.
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#3 Filip Plesha

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Posted 21 January 2006 - 05:58 AM

I am interested in tripple exposing colour reversal film through Red Gree and Blue filters respectively. This if for an experimental film and I don't need or expect 'true colour' as a result - but something sometimes close would be desirable.
Anyone know if it is possible to get a set of filters designed to work together in this way? Surely technicolour cameras used some technique like this combined with semi-silvered mirrors. Certainly I can purchase red, green and blue looking filters and see what I get, but the respective intensities of the three colour filters would greatly effect the composite colour. Are there such things as 'colour separation filters'?
Any thoughts would be appreciated.
Regards,
Ricahrd Tuohy



What do you hope to accomplish with this?

If the filters are pure and let only red green or blue light through, then the image will look exactly like if you didn't shot it with those filters, exept that you will have a layer of glass or gel in front of your lens.

If the filters are not pure RGB, then the image will be overexposed because:
For example, you expose the red component, only the red filter lets through a bit of blue and green too, so the other two chanels get exposed a bit, same happens with other two chanels.
The result is each chanel gets 1 full exposure and 2 weaker exposures.

The end result is the same as if you exposed it by half a stop more without any filters with some possible change in color balance if the 3 filters are not equally impure.


What did you think you'd get? A different look? Nope. It looks identical with possible variations in exposure of all or some chanels.
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#4 Matt Butler

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Posted 21 January 2006 - 07:00 AM

The filters to achieve the tricolour effect are:

RED - either a Wratten #25 or #26, BLUE - Wratten #47, GREEN - Wratten #61 or equivalent optical filters generally available from major filter manufacturers.

For rule of thumb exposure, take you base exposure and open up 1 stop.

Don't forget to cap/cover your lens when rewinding in the camera to achieve your triple-exposure!

A sturdy tripod is a must to avoid misalignment, unless of course that is an effect your'e after.

The classic shots with the triple exposure technique are water movement -wave breaks,rivers etc., wind blown landscapes with trees, any situation that has distinct movement combined with static elements in frame.

good shooting,
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#5 Matt Butler

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Posted 21 January 2006 - 08:03 AM

Addition to my previous post - You are shooting reversal, therefore you will get a slight colour shift when using the 'rule of thumb' exposure tip.From memory you may have to give the BLUE filter about another 2 stops more exposure. The RED Wratten #26 is a denser filter and needs another stop. please test!!

I have even used 'prime' coloured perspex in red,blue and green on occasion where larger panavision filters were either unavailable or over-budget with reasonable results.

A Kodak photo booklet published ages ago had an item on the "HARRIS SHUTTER" where the tricolour filters were mounted sequentially in a vertical strip, which was then dropped in front of the lens during the exposure time on a 35mm stills camera.

cheers

Edited by matt butler, 21 January 2006 - 08:07 AM.

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#6 Filip Plesha

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Posted 21 January 2006 - 08:08 AM

Oh I get it, the idea is to get different motion for different chanels. Again I'm thinking too still :P
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#7 Andy Sparaco SOC

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Posted 21 January 2006 - 10:06 AM

This technique is more effective if you shoot B&W film
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#8 Filip Plesha

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Posted 21 January 2006 - 12:11 PM

This technique is more effective if you shoot B&W film


It would be interesting doing it with BW film, it would probably look like modern version of 3-strip technicolor.
That would be interesting

And as for color film, well aside from the interesting effects caused by different motion in different chanels, the color reproduction of still subjects would not change at all. It might get a shift in color balance, but that's all.
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#9 David Mullen ASC

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Posted 21 January 2006 - 12:44 PM

I saw an experimental short film that used this technique. Landscape shots where rocks were normal color, but a waterfall splashing over them was red, green, and blue droplets; grass was green but swaying trees were red, green, and blue, etc. The splashing water was particularly pretty, exploding into colors.
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#10 Leo Anthony Vale

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Posted 21 January 2006 - 01:22 PM

What do you hope to accomplish with this?

What did you think you'd get? A different look? Nope. It looks identical with possible variations in exposure of all or some chanels.


Here are a couple of Library of Congress sites of seperation showing pictures taken by consecutive 3 color exposures by Aleksandr Gridenko:


http://www.loc.gov/exhibits/empire/

http://www.gridenko.com/pg/index.htm


Notice the surface of the water in the Pinkhus Karlinsky portait:

http://www.loc.gov/e...es/p87-5006.jpg

Here a girl on the lefthas moved between exposures:

http://www.loc.gov/e...es/p87-5006.jpg


How long did they have to remain motionless?

---LV
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#11 Filip Plesha

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Posted 21 January 2006 - 03:55 PM

These were shot with BW film. With BW film is very much different.

BY using 3 strips of pan BW film and different kinds of filters, you can change the look of the image.
For example, by using "impure" filters, you can lower the saturation of the photograph, or just lower the saturation of some colors like reds.

When using color filters on color film, if you use different kinds of filters than pure RGB, you won't change the look of the image because your other two chanels get exposed as well. In the end you can't desaturate or change look of colors by using filters on color film. You just end up with variations in exposure.

Its because no matter how you change filters the red layer is only going to pick up red component, and the rest of the light is going to be recorded on other two chanels.
So in a way, color film "cleans up" the color difference in these filters by separating each component to its layer.

For example, if you use a pale red instead of pure red, you'll expose the other two chanels, but not with red information (which would lower the saturation) but with actual blue and green information. If then you use pale green and blue filters too, same will happen and the only thing that you changed is added extra exposure.

On the other hand with pan BW film if you use a pale red filter instead of pure red filter, you will expose the red BW chanel with blue and green information (something that can't happen in color film because layers are only sensitive to one color), now this is something that does change the apperance of color in the final image.

In short. Using 3 strips of pan BW film, and different combination of filters you can chose any combination of light to be recorded on each layer. For example, you can chose to record 100% red, 20% blue and 50% green on RED chanel.
With color film, only one color can be recorded on one layer, you can't mix layers.
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#12 Luke Prendergast

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Posted 21 January 2006 - 04:25 PM

Lee primary gels are very wavelength specific, eg 106 red and 139 green. The swatchbook has transmittance vs wavelength graphs so you can choose very precisely what you need. You could try lighting with RGB instead of filtering on camera. That could be interesting. These gels aren't spec'ed for use in front of a taking lens but may be of sufficient optical quality for experimental work.
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#13 Richard Tuohy

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Posted 21 January 2006 - 06:00 PM

Many thanks all.
What an unmitigated delight those russian empire photographs are!
I have some of the Lee filters so I will start with them, then try either Wratten filters as described, or similar optical filters.
I will be using a simple un-pinregistered camera and colour reversal - though I may try the B/W suggestions if I wish to extend the work.
Precise registration where only movement reveals the technique is not really where I want to go with this film - though it must also be done. I wish to explore more random collisions and allignments/misalignments.
Thanks again.
Richard Tuohy
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