Regarding OAG, I’m desperate enough to give it a try. I have a reflector and a
refractor to try it on.
Sent from my iPhone
On Mar 20, 2019, at 1:07 PM, Mike McDonald <mikemac@xxxxxxxxxxx> wrote:--
I know I’ve seen other people mention how stiff their AVX is and others
saying their’s is free. I’ve been assuming either Celestron or their bearing
supplier changed what grease they use at some point. Or maybe it varies
batch to batch?
On my little C6, I just don’t see how an OAG will work. I had to rotate the
filter wheel/camera just to get the focuser mounted. I know an OAG is thee
recommended guiding method for SCTs. I’ve also read some of the issues
involved in that method and it seems that being able to rotate the OAG 360
degrees around the axis is a necessity in order to pickup a guide star. I’d
have to give up the electronic focuser for that access.
Just more things for me to keep me occupied! :-)
Mike McDonald
On Mar 20, 2019, at 10:23 AM, Jim Sellers <jsellersaz@xxxxxxxxx> wrote:
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
--
See message header for info on list archives or unsubscribing, and please
send personal replies to the author, not the list.
See message header for info on list archives or unsubscribing, and please
send personal replies to the author, not the list.
--
See message header for info on list archives or unsubscribing, and please
send personal replies to the author, not the list.
