10 stop nd filters aind infrared

I'm seeing some discussion and new filters coming out that incorporate an infra red filter in neutral density filters.  The thrust is that you can get a magenta cast as the nd while removing visible light typically does not cut back on ir.  Normally the ir is swamped by visible light so no problem but as the strength of the nd goes up the ir coming through becomes more of an issue (a greater % of the light coming through to the sensor) on cameras where the normal ir filter installed over the sensor is not adequate.  Most of the discussion seems to focus on pro video.  The problem also seems model/mfg dependent which is understandable as the filter over the sensor differs with each manufacturer.  Also the problem seems to be greater with man made things like synthetics, dyes, etc.  Does any one have any experience with this?  Is it a problem in nature photography?  Canon vs Nikon vs Sony?   The filters seem to go two ways, a dye or a cutoff ir or combination of the two filter which can introduce an overall cast or a colored vignette with ultra wide lenses.  Recommendations? Tiffen, Formatt, etc.

If the filter uses organic dyes, there is likely an IR leak. Most dark organics become transparent in the near-IR. For example, black anodization on aluminum becomes transparent in the near-IR as anodization uses an organic dye. A filter made with nano-carbon particles would be more neutral. Not sure which manufacturers, if any, have that.

Vegetation has high near-IR reflectance, which is why color IR shows vegetation as red.

Here is an example of black nylon fabric, with an organic dye showing the near IR brightening (0.7 microns = 700 nm, about the limit of visible light):
http://speclab.cr.usgs.gov/spectral.lib ... 342.w1.gif

Roger

Recommendations? Tiffen, Formatt, etc.

Start by requesting a uv-vis-ir transmission spectrum from the manufacturer, the spectrum should at least cover IR out to about 1100nm if possible. In the past Tiffen have provided these on request. Then, based on you're model DSLR, search online for the ICF (Internal cut filter), lowpass or hot mirror, transmission spectrum (curves).
Some examples may be found at http://www.beyondvisible.com/BV3a-ICF.html and http://www.kolarivision.com/internalcut ... ssion.html. The spectra show the varying degrees of IR rejection that can be encountered with different DSLR models. You may notice a bit of a trend, typically the more expensive the DSLR, the better the ICF is at reducing IR contamination.
Now compare the two, the ICF spectrum will begin to reduce IR as you move further into the IR region and the ND filter will begin to transmit more IR as you move into the IR region. Ideally they should not overlap and create a transmission "window".

Lee’s ProGlass ND “uses a surface coating made from evaporated metal, and therefore provides very even absorption across the visible spectrum and through the UV and Infra Red regions." NOTE: The Big Stopper does not use this technology.

The Tiffen Full Spectrum IR ND filters use a green dye to absorb far red/IR from around 680-740nm. They are less likely to exhibit off-angle colour vignetting when used with wide-angle lenses (but is probably dependent on exposure duration). If your DSLR ICF exhibits a cut-off at 680nm (which many of the newer ones do) then this filter may just work for you.

If you have to deal with coloured vignetting due to a combination of WA lens and strong ND filter, then Cornerfix (free) may aid in correcting the issue post process.

You may find this post by John Shaw on his website helpful.
http://www.johnshawphoto.com/?s=IRND

He likes the Tiffen IRND filter which is designed to block IR but discusses that a magenta cast may still be evident when the camera is pointed down (at least when using a D800E) unless he closes the camera's eyepiece shutter and gives examples showing the difference. I'm not sure how much this may apply to other camera bodies, but I am going to watch for this effect when using this same IRND filter on my D610 if it's pointed down exposing the viewfinder to the sky.

Thanks for your response. It will take me a little while to digest the information t6b9p presented.