Mike
I’m going to try Bernard’s suggestion of using an off axis guider to reduce
differential flexure which can come from many of the components I’m using now.
As far as AVX capabilities, I’m not certain, but I don’t have the counter
balancing problems you described. Mine is very sensitive to counterweight
position.
Jim Sellers
Sent from my iPhone
On Mar 20, 2019, at 10:06 AM, Michael McDonald <mikemac@xxxxxxxxxxx> wrote:--
OK, now I’m depressed! :-( I’m not giving up yet. I still think there’s more
to be gotten out of my equipment with a lot more practice and maybe some
tuning/tweaking.
But the numbers don’t look good. My main scope/camera has 0.5”/pixel while my
guide scope/camera has 6.62”/pixel. That’s a 13 to 1 ratio in both linear
directions. Or it takes 175 of the ZWO pixels to cover the same area as 1
guide pixel! Even with “sub pixel accuracy” of PHD2, that’s being on the
short end of a long lever.
Paul had a good suggestion last night to try to even things out a bit more:
add a Barlows 2X to the guide scope. If that works, it’d bring the ratio down
to something closer to workable. If I then added the f6.3 reducer to the main
scope, that’d bring the ratio down even more. Of course then I’m getting
different images with the effective change in focal length of the main scope.
But that’s not necessarily a bad thing. With the reducer, things like the Leo
Triplets will now fit in the frame. So I’m going to try the Barlows trick
next time I’m out to see if it works. (I had originally gotten the guide
scope to use a finder scope too. But now that I have the plate solving
working, I no longer use it for that. So the longer focal length with the
Barlow won’t be a detriment in that regards.)
I still have to figure out what to do about maximizing the performance of my
AVX mount though. One suggestion has been to bias the balance to keep the
gears engaged full time while guiding. I’m finding balancing the AVX to be
challenging. The mount is so stiff, I can move the counter weight a couple of
inches either way without noticeably effecting the balance. It’s like
Celestron used molasses instead of a lubricant on the gears!
Anyway, thanks everyone for the suggestions. I’ll keep plugging away wasting
photons! :-)
Mike McDonald
mikemac@xxxxxxxxxxx
On Mar 19, 2019, at 4:22 PM, Bernard Miller <bgmiller011@xxxxxxx> wrote:
Mike,
It is almost impossible to get good guiding with an external guide scope
because of the issue you mention below and differential flexure. If you want
to get good pictures you need to get an Off-Axis Guider (OAG). This gets rid
of differential flexure. If you chose the right guide camera you can get rid
of or minimize the plate scale difference. I have a CDK17 with an FLI
Pl16803 imaging camera. It has 9um pixels for a plate scale of 0/63
arcsesconds per pixel. My guide camera is a Lodestar X2 with 8.2 um pixels
which gives me a guide plate scale of 0.58 arcseconds per pixel. This is
only possible because I use an AOG so the telescope for the imaging camera
and the guide camera are the same.
Bernard
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