[vsnet-chat 2491] Re: ST6 - IR Blocking Filter

[Seiichiro Kiyota <skiyota@abr.affrc.go.jp>]

In message "[vsnet-chat 2490] ST6 - IR Blocking Filter",
William S G Walker wrote...
 >When using BVRI filters with the ST6 I notice that the I images show a halo
 >which would probably be a gradual brightening to the edges of the field if
 >there were no vignetting. Since I'm only doing BVR photometry this is not a
 >problem as all of the filters are adequately blocked.
 >
 >But I wonder if this has any effect on unfiltered photometry. Has anyone
 >tried this with and without the IR blocking filter supplied by SBIG? Are
 >there significant differences? I'm not even sure what is causing the halo -
 >but I imagine that it's some radiation from the filter unit itself which is
 >not much cooler than ambient, which is usually about 8C to 20C at night.

I use a SBIG IR block filter and RGB filters (for tricolor image) for crude BVRc photometry when I take images with CCD 
camera and telephoto lens. Because RGB filters have significant IR leak, I need to block such leak with a IR cutoff 
filter.
But I have not seen such a halo in my images.

CDD camera has sensitivity to near 1000nm. But radiation from object has much longer wavelength at ambient temperature.
IR block filter absorbed radiation around 1000nm and re-radiated at much longer wavelength.
So, I don't think radiation from IR block filters has influence to CCD images.  

I'm not sure cause of a halo in your images.


                                                     Seiichiro Kiyota



----
 Seiichiro Kiyota  skiyota@abr.affrc.go.jp
 Laboratory of Stress Physiology
 Department of Plant Physiology
 National Insititute of Agrobiological Resources
 Tel:81-298-38-8384
 Fax:81-298-38-8347

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