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UltravioletPhotography

Full (False) Colour IR Photography


bvf

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This topic is a spin-off from this topic, using different filters to those in that topic's title: https://www.ultravio...__fromsearch__1

 

This is about getting full (and, of course, false) colours in IR. It uses the same techniques described for UV in this topic:

https://www.ultravio...__fromsearch__1

 

In outline, this approach takes 3 images in different parts of the NIR spectrum, and uses these for the RGB channels to get a full colour image.

 

To get the three images, the following filter set was used:

 

700-800nm range: Midwest Optical BP735 + R72. (The R72 is used to block the red leakage from the BP735.) This forms the blue channel.

 

800-900nm range: Midwest Optical BN850

 

900nm+ range: Midwest Optical LP1000

 

These filters give the following transmssion curves. The curves have been adapted to include typical CMS sensor sensitivity variation across the spectrum, and have been adjusted such that their heights are the same (as differential exposures are used to overcome the different transmission levels of the three filters):

 

post-245-0-39936400-1579877817.jpg

 

The first results are below:

  • The first image is a standard visible light shot.
  • The second is the full-colour IR shot. It is disappointing in that it shows only faint colouring. But ...
  • The third image is the full-colour IR shot with the saturation wound right up. Colour at last!

post-245-0-26060700-1579877996.jpg

 

post-245-0-86669300-1579878009.jpg

 

post-245-0-70062600-1579878025.jpg

 

White balancing was done against the white PTFE tile. You can see that the 18% grey target at the back is not so grey in the IR!

 

Most of the foliage (inc. the red poinsettia leaves) is neutral - I was expecting a slight cyan tinge as UV reflectance by foliage decreases slightly across this part of the spectrum.

 

The effects of manmade colourants are always interesting. Note how the green marker pen and green booklet have quite different colours to each other in IR. But the blue marker pen and blue book both become yellow (i.e. absorbing in 700-800, reflecting/transmitting in the 900+ band). And the red printing ink is completely transparent across the frequency range.

 

The red berry-like things and the darker red parts of the roses in the vase have come out cyan, indicating that whatever colouring chemistry is reflecting red in the visible region is continuing to reflect light as we move into the 700-800 and 800-900 bands, but not in the 900+ band.

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Nicely done, Bernard.

 

I have also needed to push the saturation for my IR bandpass RGB stacks.

 

I've also tried using Orange, greenish-blue, purple instead of RGB. And such-like variations.

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  • 4 years later...
Tom Lewis

Hi Bernard,

 

Can you please tell us what camera was used for these captures?

 

Thanks,

Tom

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Andy Perrin
4 hours ago, Tom Lewis said:

Hi Bernard,

 

Can you please tell us what camera was used for these captures?

 

Thanks,

Tom

Bernard hasn’t been on the site for ages (come back, Bernard!!) but he posted his equipment on the linked thread at the top. 
 

I only have some basic kit – a full-spectrum Sony A6000 with the following UV-friendly lenses:

  • Soligor 35m/3.5 (Enlarging Lens)
  • Cassar S 50mm/2.8
  • Focotar-2 50mm/4,5 (Enlarging Lens)
  • Metal El-Nikkor 80mm/5.6 (Enlarging Lens)
  • Metal El-Nikkor 105mm/5.6 (Enlarging Lens)

 

These perform reasonably well and can record images using the 315BP25 flter at the exposure factors identified above.

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10 hours ago, Andy Perrin said:

Bernard hasn’t been on the site for ages (come back, Bernard!!) but he posted his equipment on the linked thread at the top. 
 

I only have some basic kit – a full-spectrum Sony A6000 with the following UV-friendly lenses:

  • Soligor 35m/3.5 (Enlarging Lens)
  • Cassar S 50mm/2.8
  • Focotar-2 50mm/4,5 (Enlarging Lens)
  • Metal El-Nikkor 80mm/5.6 (Enlarging Lens)
  • Metal El-Nikkor 105mm/5.6 (Enlarging Lens)

 

These perform reasonably well and can record images using the 315BP25 flter at the exposure factors identified above.

I had a dialogue with Bernhard about 50mm lenses and that led to him seeking and getting the Focotar-2 that gives better image quality all over the image than the Cassar S.

Many of the older Focotar 50mm are almost as good.

The disadvantage is that you need to arrange a way to focus and mount filters on those enlarger lenses as their original intended usage was never to be used on a camera.

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