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UltravioletPhotography

Example using set of X-nite IR Bandpass Filters


Andrea B.

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Note: Please bear with me on this topic. I'm not going to be able to get everything posted all in one sitting because we have lots of things going on here at UVP Headquarters - West. :rolleyes: :lol:


 

MaxMax makes 3 Infrared bandpass filters: https://maxmax.com/filters/bandpass-ir

 

These are beautifully made filters. Each has a shiny coloured side (dichroic?) which gives them their designation as blue, green and red. The color designation has nothing to do with how the raw or false colours appear in a finished IR photo - at least as far as I can determine currently.

 

On the linked page Dan has shown some RGB stacks made with the 3 filters. My initial experiments were not quite that colourful, but that's OK. I'll get there eventually. For my first experiments I had simply wanted to explore the basics.

 

I always like to look at the demosaiced raw photo before any RGB multipliers are applied to set the white balance. This raw composite gives an idea of how the camera is really recording through its Bayer filter. The excellent app Raw Digger outputs a very basic raw composite with only minimal contrast/saturation curves.

 

 

Gear: Nikon D600 + some 35mm lens + Sunlight

 

Measurements of the raw colour casts were made over the white Spectralon. Then a square of the fully saturated colour was added to the raw composite.

 

IR BP Blue

max transmission about 93%

half-max width about 90 nm

f/3.5 for 1/500" @ ISO-400

Like other IR-pass filters which pass some high red, we get lots of false colour with the BP Blue. It has a strong Orange raw colour cast.

standard_irBandpassBlue720_20161104wf_55679rawCompLabel.jpg

 

IR BP Green

max transmission about 90%

half-max width about 65 nm

The colour cast for the BP Green is very unsaturated. When the saturation is pushed, we can see that the colour cast is Red with about a 25% contribution from Blue (so headed towards Cerise, I suppose).

f/3.5 for 1/500" @ ISO-400

standard_irBandpassGreen830_20161104wf_55655rawCompLabel.jpg

 

IR BP Red

max transmission about 85%

half-max width about 37 nm

You can see why the BP Red requires a longer exposure time. It's lots less wide and peaks out there in the 900s.

The colour cast for the BP Red is definitely Magenta after full saturation is reached.

f/3.5 for 1/40" @ ISO-400

standard_irBandpassRed940_20161104wf_55635rawCompLabel.jpg

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Before stacking up the BP R, G and B IR-bandpass filters, I want to look at the tonalities in each layer.

 

For each photo here, the raw composite from Raw Digger was converted to Black & White in Capture NX2 and then given a black point & white point adjustment to make it look more like a proper photograph. (You can do the endpoint adjustment manually with a curve tool or by applying auto-levels on the luminance layer.) Usually we would make some more tweaks to the file than just that (raise the midtones a bit? and definitely some detail enhancement). But that's not needed for these test photos.

 

The important thing to note in these examples is that the tones are almost the same in the BPG and BPR photos. This is why some subjects are not going to produce a very colourful stack without some help. :lol:

 

 

IR Bandpass Blue

mapleTree_irBandpassBlue720_20161104wf_55518rawCompBWLevLum.jpg

 

 

IR Bandpass Green

mapleTree_irBandpassGreen830_20161104wf_55508rawCompBWLevLum.jpg

 

 

IR Bandpass Red

mapleTree_irBandpassRed940_20161104wf_55496rawCompBWLevLum.jpg

 

 

PS Difference between BPG and BPR.

The little breezes show that these were two different files. But look at the stationary areas - no not many differences! Now think what happens when you put the BPG file into, say, the blue channel and the BPR file into, say the red channel. You are going to get magenta almost everywhere. So when that's combined with the BPB file placed into the green channel, you don't get very interesting RGB stacked false colours.

 

But of course the subject here is almost all foliage, so what could we expect from a tri-colour infrared RGB stack? Other subjects do produce a bit more stacked colour with help. (See the MaxMax link above for a reminder that this can work.)

mapleTree_irBandpass_20161104wf_55496_diffRG.jpg

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Tri-colour IR Stack

 

First, choose a stationary subject........ :lol: :lol: :lol:

If the breezes had been just a little stronger, we'd have had a nice Chrono-colour stack.

 

So, just look at the stationary areas please.

This stack was made by converting the raw composites to B&W and then placing them in channels.

Raw Composite RGB Stack

mapleTree_irBandpass_20161104wf_55496stackBbGgRr.jpg

 

 

Added IMPORTANT NOTE: I was using the raw composite black & whites for that stack. I need to add a stack made with the actual photos.

Added: ...and I did, just after this next one.

 

 

Out of curiosity, I difference-stacked the raw composites without placing them into channels. Remember that if you do this that the order of stacking makes a difference. This is a stack from top to bottom as BPRed, BPBlue and BPGreen.

If the BPBlue is moved to the top, then its raw orange colour would dominate even more than it does here. It doesn't make a difference, in this particular case, whether BPRed or BPGreen is on top because they are almost the same very unsaturated and close in raw colour.

Raw Composite Diff Stack, No Channels

mapleTree_irBandpass_20161104wf_55532rawCompStack.jpg

 

 

Original File RGB Stack

This stack was made by converting the original files to B&W and then placing them in channels. It looks slightly different from the raw composite stack above (first stack) because the converter is applying the usual D600 profiles & curves to the files. (That's my theory anyway. It might change. "-) )

mapleTree_irBandpass_20161104wf_55508origStack.jpg

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I must add a follow-up note here: my channel stacks may not be perfect because I was using PS Elements and not a real channel tool. They are, however, close enough.


 

So that's all I have for now for tri-colour IR stacks.

I'll check back later and see if there are any questions, corrections or suggestions. :cool: :bee:


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Big question.

 

For the BPB -> blue, BPG -> green, BPR -> red assignment, MaxMax got cyan coloured grass.

I did not.

 

Now I'm confused. But I'll have to figure this out later.

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Andrea,

 

Interested to see your IR Tri-colour work - that might be my next project after I've done more on UV Tri-colour.

 

As you say, trees and vegetation are not an ideal subject for tri-colours because they tend to move! But there is another reason why vegetation may not be a good subject for IR tri-colour: the IR reflection spectrum of typical leaves is pretty level from 750nm or so to about 1300nm, so you're not going to see a lot of colour in your results. You might get more interesting coour by having a go with non-plant subjects.

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You definitely have to get into SWIR to see interesting variations for the most part. (Exception is that water peak I’ve been exploring.)
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The swapping of filters on the same camera/lens introduces a temporal aspect to the ensuing photography. Sometimes, this can deliver more interesting results than the combination of tri-colour IR bands themselves.

 

Nikon D600 full-spectrum, 200/4 + X-Nite filters

 

A08040371443_tricolour_XNite.jpg

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  • 4 years later...

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