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Subject: [M]: RE: Peak inside 216xt
From: Heapy Chris CG
Reply To: mapug@shore.net
Date: Thu May 07 00:50:10 1998

If the image is out of focus on one side of the chip I would hazard a
guess that your chip face is not orthagonal to the image plane, either
because the chip itself is not mounted correctly, or the image plane
produced by the SCT is at a slight angle (main mirror not square-on?),
or even the reducer not seated in it's cell correctly.

Check that your arrangements for connecting the camera to the scope do
not introduce such an error. Secondly, determine which side of focus the
'out-of-focus' portion of the chip really is. See if you can correct
with adjusting focus in that direction. This would tend to support a
problem with the image plane rather than distortion caused by the
reducer. Would be nice to check the camera/reducer on another scope to
determine whether it's the scope or camera which is responsible.

Chris Heapy

>----------
>From: Graham, Glenn[SMTP:glenng@analogy.com]
>Sent: 07 May 1998 06:41
>To: mapug@shore.net
>Subject: [M]: Peak inside 216xt
>
>Well, a few days ago I mentioned a potential problem with my 216xt when
>used with a Optec 3.3 reducer due to how far off center the CCD chip
>was. I was worried that it was far enough off center to be outside the
>useable field. I asked for reports from others that have 216 and 208
>cameras to see if this was unique (no replies, thanks everybody). Well I
>measured things and found the chip was about 1mm off center which, for a
>chip only 3.2mm x 2.5mm in size, that is quite a bit. I then checked the
>Optec web page and found that they were getting reasonable results with
>chips around 11mm in size when used with the standard SCT visual back
>like I have. So, the cause of the out of focus stars near one edge of
>the chip may not be due to the offset chip and reducer combination. I'm
>still not convinced and will do some more testing.
>
>As the message title implies, I finally took a peak into the camera
>head. I was wondering if I could adjust the position of the CCD myself.
>Earlier, when this subject was discussed, I recommended against opening
>the head due to the fact that it was flushed with nitrogen during
>assembly. I was then corrected by someone else on the list that they had
>opened it and that this was not the case. This may be true if you open
>the BACK OF THE CAMERA, the side with the button (I don't know I haven't
>tried) but it is NOT true if you open it by removing the plate on the
>CCD window side of the head! After removing the 5 allen head screws I
>found that the plate put up some resistance to being removed. Once I
>managed to work it off I found that the resistance was due to the O-ring
>gaskets used to provide a tight seal in order to maintain the "dry"
>atmosphere around the chip to prevent frosting when is cooled. In
>chamber, everything is lined with thin foam sheet to provide insulation.
>The chip is mounted on a cold finger (mine having been placed slightly
>off center). There are two screws that I suspect provide some kind of
>tuning. Having been surprised once already I decided not to go any
>further or attempt any adjustments. I did take the opportunity to clean
>the inside of the window which had some debris on it (it was not clean
>in there. I even blew out a piece of lint next to the CCD chip). Due to
>our fairly low humidity here, I don't think there is enough moisture
>trapped inside now to cause frosting problems but I'll just have to wait
>and see.
>
>So, I still would like to hear from others that have 216 or 208 cameras
>even if your chips are centered just fine, and second, don't open up you
>cameras. Nothing in there to play with and they are flushed with
>nitrogen and sealed.
>
>Glenn Graham
>