I had bought a DSIC last year and recently acquired a DSI Pro without RGB filters. It does not come with any Infra-red filter. Up to rencently I was using a Newtonian telescope so I did not need a IR filter for monochrome imaging, however I added a small barlow lens of  about 1.25X to increase the image size on smaller objects and I notice that stars do not come into focus as well as without the barlow lens. I think that the barlow does not focus the IR light at the same focal point and thus the focus appears to be not as sharp as it should.    

 To try to prove my point I tried to use the IR filter that came with my DSI-C on my DSI Pro. I immediately saw that the sensitivity of the camera seems to have dropped quite a bit. I seem to have lost almost 2 magnitudes for an equal exposure time. Also the histogram seems to have shifted down by a factor of 3-4 for both the low end and high end when a picture of the my very light polluted sky is taken. I suspect that the IR filter that came with the DSI-C has poor transmission in the visible spectrum.Looking at specs for various IR filters most filters indicated over 90% transmission over the visible spectrum. However I could not find any info on the DSI-C infra red filter.

Does anyone have any info on the DSI-C infra-red filter or any data regarding the sensitivity of their DSI Pro with and without the IR filter?

   I am considering buy a decent IR filter like the lumicon or BAADER filters but if I still loose 2 magnitudes when using an IR filter over no filter at all I might as well buy another Newtonian telescope with longer focal length to increase the image size without having to increase my exposure time by a factor of 3-4.

Hi, Claude

I suspect there is another variable unaccounted for in your test. The Meade (& most other) IR filters pass around 98% or more of the visible spectrum. You should not be able to tell any difference at all in practical use.

I have used the Meade color camera IR, the Baader UV/IR, and the clear Meade IR filter for the Pro all with good results.

Chuck

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Chuck Reese
CDIP Certified: Nebula, Galaxy, Solar System, Stars & Clusters Imager
CDIP Mentor: Nebulae & Solar System Categories
For information on the Certified DSI Imager Program, see:
http://autostarsuite.net/forums/1427/ShowForum.aspx

I am beginning to suspect a defective IR filter, since I have also tried to use a laser pointer with a weak battery so that the light is not to bright to damage the DSI Pro sensor. Since laser are monochromatic there should be no IR light coming from the laser, so I pointed the laser directly at the image sensor without any lens in between, the image formed on the image sensor is a function of the diffusion of the laser and turned out to be a fairly large circle on the acquisition window. I got essentially the same kind of data, with the IR filter the brightness of the circle is about 3 times lower than without it, both the histogram and the pixel brighness as read using ASIP confirms this again. There is no focusing involved in test test so focus cannot be an issue. I don't know of any other variable here that could affect these results.

   I would like to know if anybody else has tried taking picture with and without the IR filter with similar resutls.