Centre CSP in eyepiece and take a photo and find the centre of shot out by ???
Is this just due to the nature of T adapters and using a single screw to fix into focuser? If I screw the T onto the focuser would this still happen?
Good question, and another: Does it happen that this arrangement of one screw, and I suppose even two, rather than, say, a compression ring, tend to through the CCD sensor of the camera out of square to the light-path and basically giving the same results as a flexure problem?
Thinking about it I'm more inclined to think it a bit of both weight of camera pulling down on focus tube and the single screw putting pressure to one side.
Hmmm. I guess at the end of the day that which matters is where the image lays in the eyepiece and as long as the image captures the target alignment is not affected?
Peter, if this is a problem for you, and you need something precisely
centred, you could drill and tap two more holes, and then you would have three equidistant screws to centre the focuser tube with. The camera and
the focuser tube normally sag as one entity, so the squareness would be retained.
If the connection between the camera and the focuser tube was sloppy,
so that you had camera sag only, the sensor would be out of square.
The malalignment would often be unnoticeable, unless the scope passed
the zenith, and then the camera would flop in a different direction,
ruining your pic.
raymo
do barlows screw onto the focus tube and t adaptor? Or can be screwed on. That would remove one issue.
It was just a shock to see the difference. After getting as close as I did then see this image so far off. I can understand why and can ignore.
Barlows vary in construction. Most slide into the focuser tube like an
eyepiece does, and the eyepiece then slides into the Barlow. With many
Barlows you can unscrew the lens and use the Barlow as an extension tube.
A few Barlows screw directly onto the bottom end of an eyepiece.
The easiest way to use a standard Barlow for imaging is to use a fixed or
adjustable camera adaptor for eyepiece projection, unscrew the bottom half of the Barlow and slide it into the adaptor as you would whatever
eyepiece you normally use.[ The top half of a Barlow is usually too large to fit inside the adaptor]. As T-rings are normally snug fits onto the camera, and the Barlow [or eyepiece] is tight in the adaptor, and the adaptor is tight in the focuser tube, the only weak link left is any slop in the focuser tube itself. Fixed EP projection adaptors are cheap on Ebay.
raymo
Last edited by raymo; 27-09-2014 at 02:35 PM.
Reason: correction
