Imaging Artifact?       

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A little bit of information on the above images. These were taken with the Moon about 44% but not anywhere close as best as I can tell. In fact I believe the Moon was in the west when these images were taken with the telescope facing east so I don't think they are having any affect other than possibly some gradient. The optical tube is a 12.5" RC and the imaging equipment is a SBIG STL-11000, CW8 w/LRGBHa filters, AO-L, and Pyxis 3" rotator. I didn't notice these arcs until after the raw data was already acquired. The above images are raw uncalibrated images stretched quite a bit to clearly show these arcs. M45 data was acquired first and only has a single arc in the upper left corner of the image and that's true in all of the 12 - 20 minute subs acquired. The M44 data was acquired next and clearly shows multiple arcs with two on the bottom, two on the right side and one in the upper right corner. The data was acquired between    December 31 at 7:44 PM and ending on January 1 at 4:01 AM. All images taken at -35° binned 1x1. I have imaged close to the Moon before and have not had these artifacts or reflections as a result. I'd try to replicate this this evening but it doesn't look good weather wise. Images taken on December 29 at 3:26 AM of M44 do not show these arcs. The Moon then would have been at 26%.

Update 01/02/2012

Bob Franke, a member of the SBIG Forum replied to my request for help and recognized this pattern from an issue that Mark Manner had experienced in the past with his AO-L and MOAG as being reflections off the AO paddle. Mark was able to eliminate his by using Velcro to flock the square side of his AO-L where it connected to his AstroDon MOAG. While this didn't cure my issue it certainly got me to the proper cause but in my case I also needed to flock the Optec AO-L 3" Pyxis adapter. While that is about 3/4" deep I decided to cut my flocking material, Protostar flocking paper, to an additional 2", which while still having the backing paper on this additional 2", inserted freely into the Pyxis giving some additional reflection protection. It may not have been needed but it certainly didn't hurt anything. The image below is the same data acquired from the identical ACP plan used for the above M45 with exception of the added flocking. The image is 1 - 20 minute each of red, green, and blue calibrated and combined for the RGB image. Notice the arc in the upper left corner no longer exists.

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Update 01/08/2012

Further testing after removing the additional 2" of loose flocking paper, flocking additional shinny surfaces both in the rotator and adapter. Extreme stretches continue to show the arcs. I went back to when I originally received the STL-11000 and did not have the AO-L in place and could not see these arcs at all. After installing the AO-L several months later it appears these arcs appeared. This however doesn't convince me that the arcs are caused by the AO at all times but maybe due to the nature of the AO itself with tilting and tipping while corrections are being made is causing the light path to bend enough to possibly strike a reflecting surface causing the arcs. None the less finding this cause and effect is proving to be a challenge. The arcs are most prominent on very bright objects and blend into the background in images such as M33. Please see the image below. It is a single 20 minute luminance taken during an almost full moon and the quality of the image is not at question but rather the arcs of which there are two. One in the upper left corner and one on the middle right side.

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Update 01/12/2012

No moon at this time and only time for a few 20 minute images due to incoming clouds and wind. This single 20 minute highly stretched red image is bin 1x1 and shows no signs of the arcs as above. Maybe an improvement but will need to do additional imaging to make sure. Maybe just an influence of the moon after flocking was done. I had taken moon images using the Ha filter and stretched them ridiculously far didn't see anything out of the usual.