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Monday, October 6, 2008

Baader Coma Corrector and the Sculptor Galaxy

Unguided, 247 x 15 second JPEG frames, 1600 ASA, with noise reduction. The camera was also fitted with a Multi-Purpose Coma Corrector (MPCC) from Baader Planetarium, Germany.

The MPCC attaches to the T-ring right in front of the camera, and comprises what appears to be 2 lenses complete with 7 layer coatings to provide a completely flat field and eliminate coma from the fringes of the field of view.

Well, I've definitely observed an elimination of coma around the edges of the larger master photograph (all my images are cropped to scale to a widescreen display). But, any time a lens is introduced less light makes it through, and two or three elements (lenses) has some impact. You can see in the image that the diffraction lines are barely visible and the stars less point-like.

Another unexpected downside due to the proximity of the MPCC lens surface to the CMOS sensor, is the radiated energy from the active CMOS sensor electronics in the camera being reflected right back onto the sensor! Arrrgh, this adds more noise the point it interferes with getting a cleaner image. I've taken several other photos so far with and without the MPCC, and the additional reflected noise is consistent. Never occurred to me before I bought the thing.

Its my opinion at this point, dealing with coma means spending more for a higher quality instrument such as a Mak-Newt, SCT, or of course an RC telescope. There is a hybrid made by Vixen, the VC200L, where the front plate is removed and a 3 element corrector optic is placed at the end of the focuser assembly. Comparable light loss might be mitigated by the fact it has an 8" aperture rather than 6" in my scope. Its possible the VC200L lens surface is far enough from the camera's CMOS sensor (at least 3 or 4 inches) that it might reflect very little back.

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