10 stop ND instead of IR filter

[Ron Marshall]

I want to try IR film but don't have an IR filter.

Since an IR filter such as the Hoya RM72 absorbs all wavelengths of visible light, as does a ND filter, would I get a similar effect from IR film using my 10 stop ND? (Assuming of course that the IR sensitivity of the film I choose is not much less than its sensitivity to visible light.)

Thanks for the assistance.

[Bob Salomon]

Your ND filter is reducing visible light not passing a particular wavelength of IR or UV light.

To give you an example following are the IR filters made by Heliopan. Each one passes light at the filter's value in the IR spectrum.

RG 610, RG 630, RG 645, RG665, RG695, RG715, RG9, RG780, RG830, RG850, RG1000.

Your ND filter doesn't do what an IR filter would do. But if you own a yellow 12, dark red 25, orange 22 or green 13 you may be able to experiment with false color IR.

[Ron Marshall]

Bob,

Does a ND filter block much IR?

[Matthew Cromer]

Most ND filters block much more visible light than infrared.

I use an ND filter with my Sony 828 in nightshot mode and it's almost all infrared light that gets through.

[Ron Marshall]

Schneiders website has the answer: starting at 700nm only twice as much IR as visible is passed by the ND, and by approximately 800nm this is up to about 5 times.

So I will need to buy an IR filter.

Thanks for the responses.

[Chris Gittins]

I just checked the Edmund Instrustrial Optics website. The ND filters I found were specified for 400-700 nm. You could try contacting them and asking for a plot of transmission vs wavelength too. I wouldn't have guessed transmission would increase as rapidly at longer wavelengths as you cited above, but that just goes to show you what my intuition is worth.

[Roger Scott]

Hi Ron,

Try an unexposed but processed sheet of E6 film. It's close to an 89B/Hoya RM72 and blocks most visible yet passes through IR. This is the basis for the dust detection in high quality scanners (dust doesn't transmit IR).

Regards,

[Ron Marshall]

Thanks Roger, that's ideal.

[Paul Moshay]

I tried 2 thicknesses of unexposed but processed E6 film in front of my Nikon 775 digital camera and got some fine looking IR images. Using only one thickness made a semi IR look as some reds in the flowers came through. I liked the two sheet images best.
Paul