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Low end mount for C11 for modest imaging?

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#1 astrovienna

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Posted 03 June 2009 - 11:41 PM

I'm about to move to a C11 from my old 8" Nexstar GPS. The mount is the question. I do some modest deep sky imaging with a DSI II (probably a DSI III soon) at f6.5. I get to dark sky sites almost never (whimper!), so the scope will stay permanently setup on the very short pier in my backyard observabox. You can get an idea of my imaging goals/skill level with a quick look at the images posted on my web site, linked below.

A CPC1100 will cost $2600 these days (I already have a wedge). For just a few hundred more, I could get the same scope on a CGEM or EQ6 (Orion's Atlas is really an EQ6, right?) I think to get to the next quality level of mount would cost another couple thousand (G11) which I can't spend.

I'm basically familiar with the fork vs. GEM issues (eg, meridian flip, circumpolar access), but what I really can't determine is how the different mounts compare on tracking. That's the key issue for me. Which of these three mounts (and if there are others in this range, feel free to include them) will deliver the best images? If they're pretty much equal, I would lean toward the CPC1100, having used forks for all of my 25 years in this hobby. (Serious years - the decade with the Sears 50mm refractor doesn't count!)

I should note that I'm no mechanic. While I'm pretty sure I could handle the ball bearing replacement in the CPC1100, much more than that would be beyond me. So if a given mount can get nice results, but only with re-engineering, that might rule it out.

I know the fork vs. GEM debate always rages, but I haven't found any threads that are really on point since at least 2006. So I would really appreciate any recent thoughts. Thanks in advance.

- Kevin

#2 ZRX-Steve

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Posted 04 June 2009 - 02:05 AM

I noticed a very nice hypertuned EQ6 on astromart today. The ad shows an excellent periodic error results graph. For $1550 it would be a great candidate.

#3 Luigi

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Posted 04 June 2009 - 06:50 AM

Seems the current preponderant use of autoguiding has largely removed tracking problems as an issue. Most common mounts work quite well when used this way, as long as they are sufficient for the load. For a C11 on a GEM, a CGEM, or Altas (EQ6) would be OK. (I owned a C11/G11 for 10+ years). IMO a CPC would be more comfortable for visual. I haven't seen much AP done with one though. With the GEM, you get to carry and set up the mount and OTA separately whereas, obviously, you have to heft the whole enchilada with a CPC. Mounting it on a wedge makes it more of an achievement.

#4 AlexN

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Posted 04 June 2009 - 06:56 AM

I used a C11 on an EQ6 for imaging at F/6.3 and it went well even with a heavy guide scope... It took me some time to iron out a few guiding issues, but once I got it all under control I got quite a few very nice images... I sort of wish I'd kept the C11 now that I've got a self guided camera and adaptive optics... Would probably be awesome.

Good luck..

Ps, the mount Steve linked above would be a VERY nice candidate for your needs.

#5 Chris Curran

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Posted 04 June 2009 - 07:06 AM

I owned a C11/G11 for 10+ years

A buddy of mine has this setup. Nice rig...

#6 Bowmoreman

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Posted 04 June 2009 - 08:06 AM

I hope OP is ready for all the "issues" that will be associated with trying to image at 1800+mm focal length...

Like seeing, steadiness, etc... (Seeing will be the biggest - most likely).

yeah, autoguiding will help... but that's a loooonnnngggg focal length to be playing with if one doesn't have a lot of experience. Yeah, with a reducer it's better than the native (2800mm?), but still, most "experts" (of which I am not yet by any imagination!) suggest starting in imaging at/below 800mm for least frustration...

that said, if OP is comfortable imaging with the old C8, then going with a C11 on a GOOD EQ mount (EQ6 or above, but, preferably a CGE or G11) won't be impossible...

Maybe score a used CGE for around $2K??? Versus $1500 for EQ6/Atlas or $1799 for CGEM? Just a thought...

Clear enough skies

#7 astrovienna

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Posted 04 June 2009 - 10:32 AM

Thanks for all the feedback, folks. Several suggested picking up a GEM secondhand. If I had experience with a GEM, I might go that route, but having never used one before I am very concerned that I would spend a LOT of time trying to figure out whether problems were caused by me or the mount. On a fork, at this point, I'm much more confident that I could quickly answer the me vs. it question. I would definitely consider a new GEM from a reputable dealer, but with a used mount of any kind - well, you're on your own for troubleshooting, and I got burned on a used mount before.

I'm not too worried about imaging at f6.5. I was pleased with my results on the 8". You can see the images on my site - that's what I'm shooting for. (You can never be disappointed when you hold yourself to low standards! :jump:)

But I still have that bottom line question. Does anyone know how these mounts compare for tracking purposes? A lot of folks have mentioned that they image with GEMs, but does anyone have experience with both fork and low end GEM? I don't think a CPC fork is going to match a G11, but is there any reason to think that, well tuned, it can't get the same results of that hypertuned EQ6?

- Kevin

#8 Psyire

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Posted 04 June 2009 - 10:56 AM

My personal opinion would be to go with a CGE class mount. Anything less and your tolerances are pretty tight at the Focal Lengths involved with a C11. I'm not saying it can't be done, because it has.. but I wouldn't want the frustrations that go a long with it. When spending a decent amount of money you should be happy with the results..

#9 Psyire

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Posted 04 June 2009 - 10:57 AM

Out of curiousity, which wedge do you have?

#10 astrovienna

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Posted 04 June 2009 - 11:04 AM

Out of curiousity, which wedge do you have?


The Celestron "Heavy Duty" wedge. I know, I know. But it has worked out basically okay, especially on my pier. I have, however, occasionally wondered if I should have just modified my old Super C8+ wedge, which was single-piece cast, to fit the Nexstar's base.

#11 hapo

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Posted 04 June 2009 - 02:22 PM

C11 is best mounted on a CGE, it is rock solid even when focusing at high power and the CGE is tracking better. You only see mirror shift at high power, no vibrations from touching the ota.






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