Infra red filters

[shaun]

Hi

I want to try shooting some black and white infra-red images with a hasselblad h3d1139. The filters are quite expensive so I was wondering if anyone has tried and liked the results or been disappointed compared with the images that I have seen with IR filter removed from cameras.

Shaun

[tonyhowell]

I bought an Infrared filter and used it on my Phase One 645/P45. It does give a unique look, like very early photography, but made the images too soft for my liking. I keep toying with the idea
of a Canon 5D converted, but want to see if the images are sharp first!

[shaun]

Hi Tony

Thanks for the reply. Wasn't expecting softness, could it have been the way you have to focus differently for IR or do you think it's an issue that will always be there with filters, which brand of filter did you use?

Shaun

[ondebanks]

One gets soft images in IR photography for 3 main reasons:


1) The one that everyone knows about: Focus shift with wavelength - you can refocus to the "IR mark" (or guessimate, or "chimp", or rely on DOF), to offset this.

2) The one that people forget about: The lenses are not chromatically or spherically (sphero-chromatism) corrected for wavelengths outside the visual spectrum. The focus shift is a symptom of this, but refocusing only partially fixes it. The residual abberations smear the focus and this cannot be fixed.

3) The one that almost nobody knows about: IR photons have a much longer mean-free-path in Silicon than optical ones, so they are absorbed over a much deeper range in the sensors, and the electrons they release are gathered into a wide spread of pixels around the one that they "should" be gathered into. Again, this cannot be fixed.


Reasons 2) and 3) mean that you are better off with a larger sensor, however.

Ray