Coma correction - WHAT am I doing wrong?

[lukebl]

ok photos

Thanks for that. Not sure what the pictures tell me, though.

[Starlight 1]

Look at the photos on the right ,the secondary is well over to the left of the cross.

[Starlight 1]

How is it going Luke any luck.

[lukebl]

How is it going Luke any luck.

Sorted, I think. After much fiddling with the secondary, a few quick images last night show rounder stars. Need a proper imaging session to see how it all looks.

[terrym2002uk]

Out of curiosity, could you define fiddling? Would be intrested to know what you have done to resolve this. Also some pics down the focus tube would be nice to compare against your originals.

[lukebl]

Out of curiosity, could you define fiddling? Would be intrested to know what you have done to resolve this. Also some pics down the focus tube would be nice to compare against your originals.

Well, as I said originally, I was a bit bothered that when the secondary was central to the tube (i.e when the distance to the edge of the tube when measured along the vanes was equal), it wasn't central to the focus tube. When I had the problem with the oval stars, the secondary had been lined up with the focus tube, not as described above. So I reverted to ensuring that it was central to the tube, used a collimation cap to line the secondary with the primary (ensuring that I could see all retaining clips on the primary) then collimated the primary with a Cheshire collimator.

To be honest the view down the tube doesn't look any different from the image I posted earlier. I think that the only reason you can see part of the focus tube is that the secondary is rather large on the 250pds, so shows a greater area.

The message is that collimating the primary mirror is an absolute doddle, as long as your secondary is collimated properly.

[terrym2002uk]

To be honest the view down the tube doesn't look any different from the image I posted earlier. I think that the only reason you can see part of the focus tube is that the secondary is rather large on the 250pds, so shows a greater area.

QUOTE]

I'll be getting a MPCC to pop in my 200PDS and have been watching your thread closely. The view down my focuer is pretty much the same as yours, ie edge of focuer tube in view. I collimate mine with the secondary centered in the tube, ie using the vanes, then adjust the secondary so the 3 primary clips come it view, and check it with a laser (ie it hits the donut). After that its a tweak to the primary and all done. Does that sound right?

[lukebl]

...Does that sound right?

Sounds good to me. Well, that's how I do it too!