CGEM Edge C8 sutitable for AP at 2000mm FL?
Posted 13 January 2010 - 04:01 PM
Anyone has 10 minutes or greater subs at 2000mm FL with C8 and CGEM? It does not have to be Edge C8. If so, please attach photos.
If CGEM is not suitable, then probably Losmandy G-11 would be the next choice even though it costs twice as much. I would rather have CGEM mainly for easier to use hand controller than G-11.
Posted 13 January 2010 - 06:54 PM
Posted 13 January 2010 - 07:32 PM
I had C-11 with Atlas EQ-G and C-11 was too heavy for AP for the mount. Atlas EQ-G load capacity is about the same as CGEM. I wanted to know if CGEM is stable and durable for 10 minutes plus guiding for C-8 at 2000mm. The only disadvantage of Atlas EQ-G is the latitude adjustment bolt is extremely difficult to raise latitude while the heavy scope is mounted. I read from this forum the CGEM latitude requires much less effort to adjust while scope is mounted.
I am more interested in narrow field than wide field AP like M27, M57, etc.
Posted 14 January 2010 - 08:05 AM
Since the CGEM comes with and auto guider port, I don't see why it would not work for auto guiding over ten minutes.
I'll bet the mount will autoguide for a lot longer than 10 minutes, but the performance may not be adequate for what will be needed at the image scale you'll have at 2000mm.
If you use binning (or go with a cam that has very large pixels), so that your image scale is approaching a couple arcsec, you'll have much more success in the guiding department (though lower resolution).
Alternatively, get a good focal reducer, or try the HyperStar approach.
Posted 14 January 2010 - 08:54 AM
Posted 14 January 2010 - 10:23 AM
I am trying to minimize weight like using OAG instead of guide scope. Adding AO would add a little more weight to the rear making it more difficult to balance a back heavy and short tube C-8. It may require adding counter weight at the front.
Posted 14 January 2010 - 10:55 AM
I understand your concern about long exposure on a CGEM with that much FL and weight. Celestron advertises C11s on CGEMs for AP which is scarey. The same goes for the CG5 and C10 newt. Having experienced one of those configs myself and knowing it couldn't handle real long exposure times, I'd be skeptical without seeing some examples too. Granted a CGEM is much more refined than a CG5, and does have PEC, it still will have some accuracy limitations and the payload capacity isn't much different. I'v guided a CG5 at 1200mm with 18 lbs up top close to 10 mins, but without PEC the mount would jump every gear cycle (10 mins) too far for autoguiding to iron out without losing the exposure. So I worked with 4 min subs or very short FL to compensate. My guess is that the CGEM will perform closer to a CGE than a CG5 due to the improvements in design. I've seen decent images from CGEM owners with long exposure times, but not at 2000mm or more. I'm just as curious as you are to see those examples.
Posted 14 January 2010 - 11:37 AM
Money is not really an issue for me. It's the software in CGEM hand controller that's seems to be much easier to use than Losmandy. I guess I just have to learn to use Losmandy's Gemini hand controller and get used to it. I read the Gemini operating manual and it has a steeper learning curve than CGEM but that's ok. It would be nice to integrate CGEM handcontroller with Losmandy G-11.
Posted 14 January 2010 - 11:59 AM
It would be nice to integrate CGEM handcontroller with Losmandy G-11.
A CGE would be just about that.
Posted 14 January 2010 - 12:22 PM
Posted 14 January 2010 - 12:52 PM
Getting 10+ subs at 2000mm is a tall order for just about any commercially available mount under $5000. It won't the amplitude of the PE that will be the most concerning it'll be the noise and the transitions on the PE curve.
A good example of a CGEM might be able to do it but a CGE or G11 is likely a better starting point. Either way you're likely into some tuning and upgrades unless you spend really big bucks ($7000+). I think you're best option would be a new G11 with a series of upgrades such as the Ovision worm. That combination won't be cheap though ($3700+). I'd also consider if possible a pier mounting to remove the tripod from the equation.
Posted 14 January 2010 - 01:01 PM
Posted 14 January 2010 - 01:18 PM
All gems do the meridian flip at some point ... the differences in the mounts (physical and software) just determine where in relation to the meridian they do the flip. The better question is how far past the meridian does a mount travel before it has to do the flip.
Yes. The reason folks talk about the CGE having issues is that it has a safety feature - it stops tracking a bit past meridian rather than cranking along until something expensive runs into something solid. My LXD750 did that also - it's a nice bit of cheap insurance against carelessness (or falling asleep).
If the flip is inevitable then it doesn't really matter where it happens - it's once per night.
Regarding shooting at sub-arcsecond resolution: none of the mounts mentioned so far in this thread make any promises whatever about periodic error. Guiding them down to less than an arcsecond may be possible but it's probably not a suitable task for a beginner. Better to use a mount that DOES specify PE at a reasonable level. For a C8 I'd recommend an EM-11. It's in the same price class as a G11 but much more precise. You can have excess capacity or extra precision for the same money - but it'll cost you much more to have both (though, come to think of it, you could probably pick up a used EM-200 for about the same money and have both). I'd vote for precision unless you are ready to reduce your expectations in terms of resolution. Just be aware that the Tak mounts (like the Losmandy mounts) lack the safety feature mentioned above.
Posted 14 January 2010 - 01:30 PM
Yes, I know GEMs do meridian flips at some point. Several can cross meridian without restrictions. But is CGE more restricted than other GEMs? In other words, can you set the CGE meridian flip point like G-11 can or is the CGE "hard-coded" to flip as soon as it touches the meridian? If so, I don't want it.
Very few mounts do an automatic meridian flip when tracking. Maybe the Paramount? The "flip point" you mention that is selectable has to do with which side the mount will use for a goto operation to a point near the meridian. If you permit a Losmandy to cross the meridian while tracking, it'll just keep going until somebody or something makes it stop. I don't remember where the stop is on the CGE; maybe 15 degrees or so past meridian? That's where the LXD750 would stop.
Posted 14 January 2010 - 01:44 PM
Posted 14 January 2010 - 01:48 PM
CGE Pro can go as other mounts a lot more after meridian, but it's a different price range.
Posted 14 January 2010 - 01:54 PM
Posted 14 January 2010 - 02:00 PM
I wonder if I can open the CGE and disconnect the safety feature to keep on tracking past the meridian? Anyone done that?
Posted 14 January 2010 - 02:14 PM
I wonder if I can open the CGE and disconnect the safety feature to keep on tracking past the meridian?
No, you can't.
If this meridian issue is really important to you, you might consider a CPC800. That'll track horizon to horizon without a hitch and without any collision danger, and probably with better tracking precision than anything less expensive than a CGE or G11.
If you want to be able to shoot well past meridian, and are willing to take a chance on collisions, then my EM-11 or EM-200 recomendation stands.
Posted 14 January 2010 - 03:09 PM
Will CPC800 with heavy duty Mitty Proline wedge work well for AP at 2000mm FL?
Posted 14 January 2010 - 04:36 PM
It looks like I may end up getting Losmandy G-11... It's the software in CGEM hand controller that's seems to be much easier to use than Losmandy.
I've used the ASGT (CG5), and now the CGE and MI250. The MI uses the Gemini controller, as does the various Losmandy mounts. The Gemini is generally more versatile than the Celestron, and in being so, has more variables. You seldomly need many of its routines, so just memorize the frequently used aspects, resort to the book for the rest.
I won't say that every 6yr old can master it, but I'll sure bet that many can. It's not that difficult.
By the way, imaging at 2000mm w/ typical cam pixels is not trivial. That's less than 1 sec/pix. The CGE was pressed to yield good results w/ the Mewlon at 3000mm using 6.45u pix binned X2 (~ same as you're discussing) w/ an OAG. The MI has yielded essentially 100% good results.
I'd still keep the AO option alive if you go w/ a G11, CGE, or EM200. It would make those stars nice and round (and keep your image resolution up).
Posted 16 January 2010 - 11:00 AM
I suppose in that respect, why don't you just get AO and keep using the C11 on the EQ-G?
Posted 16 January 2010 - 11:50 AM
I have already considered fork mounted with wedge but many people voted against it because it's not as stable as GEM. Also it's harder to balance fork mounts than GEMs. There may be vibration issues while tracking with fork/wedge setup.
Will CPC800 with heavy duty Mitty Proline wedge work well for AP at 2000mm FL?
Posted 16 January 2010 - 12:15 PM
why don't you just get AO and keep using the C11 on the EQ-G?
I no longer own them. I am looking for smaller size scope for better portability.