STXL 11002 and FW8G-STXL

Discussion in 'General' started by Richard Asarisi, Jun 1, 2016.

  1. Richard Asarisi

    Richard Asarisi Standard User

    Mar 5, 2016
    I'm having a real hard time getting any stars on my pick off mirror of my FW8G.
    I've tried to get the pick off mirror to give me an image but I never was able to see any stars on it. I slew to m13, and then I moved the cluster to the edge of the ccd field where the pick off mirror is. Then set the auto guide imager to run a series of shots for 500 times, all the while I was adjusting the focus of that mirror. It kept giving me images but I never got anything that looked like stars or donuts. Maybe I'm still doing something wrong. Here is a test shot of M101. You can see the shadow of the pick off mirror, I assume that this puts it in the light path but I could be wrong about that too. I now have the pick off as far into the main ccd as it will let me move it.
    For all intents and purposes the ccd in the SBIG 11002 is full frame so I'll use a 35mm frame, which is 36x24mm.The largest circle it can fit is therefore 24mm in diameter or 12mm in radius. My final effective focal length is 2438mm. Arctan(12mm/2438mm) = 0.2820144°. That was the angle from the center to the edge, so double that to make the total view angle of the largest circle on my sensor, which is 0.5640 degrees.

    So what does that tell me? Other then the image circle is very small, but I am also filling the sensor since I see no vignetting. Which wold lead me to say that pick off mirror should be in the light cone.

    If I can figure out how I will upload a file showing the shadow of the mirror on the main ccd m101_test.jpg
  2. Doug

    Doug Staff Member

    Sep 25, 2014
    You do have some vignetting in that image, but obviously the mirror is picking off some light.

    Perhaps the guide chip is badly out of focus? Try pointing the scope at a dense open cluster so you can easily get a bright guide star. Then adjust focus if needed.

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