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Full-colour IR

TriColour
7 replies to this topic

#1 Bernard Foot

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Posted 23 March 2020 - 17:08

One of my projects this year is to try some full-colour IR work, by taking 3 shots with different band-pass filters and then using those as colour channels as follows:

Blue Channel: CWL = 750nm approx Filter = R72 + Midwest Optical BP735
Green Channel: CWL = 850nm aprox Filter = Midwest Optical BN 850
Red Channel: CWL = 1000nm approx. Filter = MidWest Optical LP1000

I'm waiting for the sun to return to try this out on landscapes - my initial trials on things like flowers and other stuff indoors has not found much by way of colour across this part of the spectrum unless I really wind up the saturation.

But there is one area where I have found colour - the sky comes out a lovely blue. This is illustrated nicely in the following photograph, taken in December - saturation has not been increased. there is some colour banding in the fence shadow at bottom-right and on the tree just to the left of the main tree - this is caused by the shadows moving between the three colour separation exposures. I also took some visible shots, which looked quite similar apart from the colour of the grass!

Camera was a full-spectrum modified Sony A6000, with a Canon EF 28mm / f2.8 lens.

Attached Image: IRFC 015 Canon Crop.jpg

Edited by Bernard Foot, 03 April 2021 - 20:31.

Bernard Foot

#2 Stefano

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Posted 23 March 2020 - 17:36

Just like you did in UV...

That blue sky is really cool, that's what made me think about the possibility of seeing stars in daytime in infrared. Basically only your "IR-blue" channel has some signal from the sky.

#3 Stefano

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Posted 23 March 2020 - 17:41

Andy should give it a try in SWIR (outdoors). I would really like to see a human using, say, 1350 nm, 1450 nm and 1550 nm. Maybe we have blue skin and yellow hair. People and water are the most interesting things to photograph in SWIR.

Edited by Stefano, 23 March 2020 - 17:42.


#4 Andy Perrin

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Posted 23 March 2020 - 22:03

Very pretty. I will eventually try it in SWIR, but I need the appropriate filters.

#5 OlDoinyo

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Posted 24 March 2020 - 01:47

Are these bandpass or longpass filters? If the latter, it might be appropriate to perform subtractions to get the bandpass signals for the first two channels.

#6 Bernard Foot

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Posted 24 March 2020 - 10:11

The blue and green channel filters are bandpass.

The red channel filter is a longpass, but is in effect bandpass because the sensitivity of a CMOS sensor ends at around 1120 nm. The graph below shows the transmission patterns taking into account typical CMOS sensitivity - the peaks for the three curves have been equalised.

Attached Image: IRFC Filter Curves.jpg
Bernard Foot

#7 dabateman

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Posted 24 March 2020 - 10:38

I like it Bernard. I will also have to give that a try.
I have a Lp700nm fiilter that I will cut with a leakyish BW486 filter. This should give me 680/690 to 760/780.
A got a BN850, for the 800nm band like you.
Also have a Lp1000, that os really a 950nm filter. Similar to yours.
So just my 700nm bandpass will cut earlier.

If I have a chance may try it an a subject in the backyard that I really like in these odd times.

#8 Bernard Foot

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Posted 24 March 2020 - 11:01

Let us know how you get on. It would be good to have ideas as to what subject types work well and show colour in IR.
Bernard Foot