infrared

[Graham Stabler]

Hello,

I was just wondering if anyone has played with infra red illumination to get penetration into/through chitin?

Cheers,

Graham

[Cactusdave]

I know regular contributor Graham Matthews has experimented with this, example photos here: http://www.gpmatthews.nildram.co.uk/mic ... acoda.html . Hopefully he will reply to this thread.

[gpmatthews]

Hi - yes, I have done a small amount of experimentation with NIR. The best method of camera use is to remove the IR blocking filter from a digital camera. This gives much greater sensitivity than trying to use a camera that has an inherently poor IR filter, as many landscape photographers have used. If you use an IR LED as light source you don't need any other filtering, but of course cannot see the image with your own eyes and will need to use the LCD screen on the camera. If you want to use a filament lamp as a source of NIR, you will need to remove the visible component. One of the cheapest ways to do this is to make a filter from a pair of crossed polarising filters. Cheap polarisers tend not to work in the NIR but will quite effectively block visible light. If you use this option you can place the filter in the camera optical train, but not in the human optical train. This then gives the possibility of using a visible image for composition and focus. Be aware, however that a parfocal setup in the visible will not be parfocal in NIR. The NIR image will not be formed at quite the same position as the visible image, and some experimentation will be needed to achieve parfocality.

Other problems you may run into include a bright spot in the centre of the NIR image. This can occur where the non-reflective surfaces inside optics which are designed to work in visible light may be reflective in NIR.

Chitin is indeed more transparent in the NIR, but I don't have a good NIR spectrum to assist in finding an optimum wavelength.

[Graham Stabler]

Thanks Dave,

I'm probably going to use a monochrome camera without any viewfinder and either LEDS or laser light for illumination. I'm hoping to get some penetration into live insects to see more of the insect flight mechanism, possibly at high speed. I'm really not sure how well it will work, will probably have to use polarizers to reduce specular reflection. Also got to avoid melting the poor insect

Graham