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toc
17-05-2011, 09:55 PM
This is a rambling first light with my Meade 12" ACF and Celestron CGEM...Please forgive my unconventional style of expression :P

Well, this has been a long time coming - Melbourne's weather has been woeful for the last few weeks, so tonight's clear sky was too much to pass up. :)

I setup at around 7:40, and couldnt resist having a quick peek at the moon. (without any cool down time) First step was to fireup the CGEM and do a 2 star alignment. That done, I slewed to the moon, and popped in the trusty Hyperion zoom eyepiece.

Initially I was really struggling to even reach focus - the image would appear to come into rough focus, but then drift away when I got closer. I assumed this was due to zero cool down time.

Not wanting to really push things further, I went inside to watch Master chef, and Bondi vet.

An hour later, I decided to get back out and collimate the scope, since it had a pretty big trip to get to me. I slewed to canopus and defocused. Immediately it was obvious that the scope was grossly out of wack. Went side and found an alan key to fit, and set about adusting the sucker!

All I can say is that collimating a 12 inch is a LOT harder than the C8. Looking through the scope while you are making fine adjustments with an alan key is somewhat tricky. ;) I need an extra few inches of arm span :lol:

After a lot of getting confused and forgetting which way to adjust, I finally managed to get pretty close - not perfect, but good enough for a first light.

Moon was back on the agenda.

Its clear to me that there is something slightly odd with the focus mechanism of this scope - not sure if its normal - I suspect not. I kept having the same issue that I had before. I would try to focus, get close, but then have the focus appear to jump back a bit. If I then focused again, I could finally get it sharp. Perhaps the center baffle just needs some regreasing? Hopefully it will improve over time, since I suspect it has not had a lot of use over the last 3 years or so. I noticed a lot of mirror shift as well. I was fully expecting to see some, but not quite as much as I am seeing.

I feel a crayford is going to be an essential bit of kit, otherwise I am going to get pretty annoyed. ;)

Any who, when in focus, all I can say is that the optics appear well sorted. Very bright, bags of detail and contrast. The full moon is not an ideal target for lunar detail, but its certainly left the old C8 for dead.

Next, and much more impressive was saturn. Wow, even with imperfectly collimated optics, Saturn was truely wonderful. Cassini was sharp and obvious, but the impressive thing for me was the colour and detail of the planets clouds. I cannot wait for Jupiter!

I was then cut short by domestic duties and helping the kids with homework, so that was the end of my very first session. Overall, Im pretty content :)

A word on the CGEM - it is a great mount, and Im very happy with it. Its clear that its really at the limit with the 12 inch, but for visual it handled it just fine.

Shiraz
17-05-2011, 10:25 PM
Good to hear that its all coming together Tim. Isn't it surprising how much difference there is going from 8 to 12 inch aperture? Regards Ray

casstony
17-05-2011, 10:42 PM
With regard to the focusing difficulties Tim, try doing the final focus with an anti-clockwise turn of the knob; this is pushing the mirror up hill and might avoid the mirror shift. I have found that the larger SCT's benefit more from a crayford though - nothing beats being able to rock back and forth through focus to be sure you're getting best focus.

toc
17-05-2011, 11:07 PM
Thanks - I will give that a go next time Im out. Im saving up for moonlite though :D

toc
17-05-2011, 11:08 PM
Im getting there :) I cant wait until I can sneek a peak at some globulars...

Merlin66
17-05-2011, 11:11 PM
Tim,
If it hasn't had a lot of use for a while, the glue/ grease on the baffle will need some spreading....
Run the focus all the way out and back all the way in a few times.
This usually improves any mirror slop. The 12" has a weight balancing spring and I've found the slop on my ol' 12" to be minimal....
Invest in a set of Bob's Knobs - makes life much easier.
Also check that the allen screws on the corrector retainer ring are ONLY nipped up - I found on a 10" I was inspecting that they had been REALLY tighten up on one side and pretty loose on the other - the Ronchi screen showed two distinct areas! After loosening the screws and resting overnight it came good.

renormalised
17-05-2011, 11:24 PM
Wait until the collimation and such is tight...you're going to be rather impressed with the ACF optics. They're very good.

The only bug with them is when you're wanting to take piccies. If you use a reducer/flattener, you'll find it hard to get one that suits the ACF optics. The Meade ones are not up to spec....especially the 0.33 one. Put that in the optical train of the ACF and it'll look like you've jumped to lightspeed :) I normally don't use them...just run at the native f ratio or go with powermates to increase the focal length. You can get reducer/flatteners to suit the ACF optics, but since the optics already produces a very flat field across the FoV I can't see why you'd want to use them. If you want a widefield scope, you get a good apo or a fast newt astrograph. Other than that, they're also very good for astropiccies.

robz
18-05-2011, 01:24 PM
Hi Tim.
This was a new OTA wasn't it?...............or am I wrong?
You mention that it probably hasn't been used for 3 years.......???

Rob.

toc
18-05-2011, 04:27 PM
Second hand...Got it from a fellow Ice in spacer...

robz
18-05-2011, 04:54 PM
Oh, I see...........had my wires crossed:D

Anyhow, enjoy the scope............it has a LOT to offer........trust me;)

Ric
19-05-2011, 09:40 PM
The 12" is a great scope Tim

To be honest I am yet to find fault with mine after 5 years.