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Nexstar 9.25 or the C 9.25 SGT?

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#1 zccopwrx

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Posted 07 March 2004 - 10:30 AM

The difference is the mounts, and a considerable price also..

Now, whats better for the use of astrophotography? The dual fork mount nexstar, or the German EQ mount on the "advanced" 9.25?

The dealer locally said he thinks the dual is better.. but most buffs here desire the german eq mount..

HELP! :confused: :tonofbricks:

#2 jrcrilly

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Posted 07 March 2004 - 10:50 AM

While a German EQ mount has advantages, there's also a large quality difference (hence the price differential). The Nexstar GPS fork mount has a much more stable and precise drive system than the imported EQ mount. If you want the quality and precision of the Nexstar GPS in a GEM the price gets even higher - that's the CGE.

#3 Don W

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Posted 07 March 2004 - 10:52 AM

The Nexstar 9.25GPS (dual fork) is better for imaging than the Advanced mount. The CGE is probably even better, which is what the 'buff's would recommend.

#4 conus

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Posted 07 March 2004 - 12:11 PM

In the end, I got mine knowing that I'd eventually sell the mount to help pay for a G11 with the Gemini Goto. In the meantime, the CG5-GT should be a sufficient mount with which to learn astrophotography basics on the moon and planets.

#5 jrcrilly

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Posted 07 March 2004 - 12:55 PM

Hi, Steve.

Sure; I haven't used one but I looked at one on display and it seemed encouraging. A lot of mount for the money and should be easy to sell when the time comes.

#6 Suk Lee

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Posted 07 March 2004 - 01:58 PM

If you end up getting a higher end german equatorial, I specifically would avoid the CGE. S&T reviewed it and found it can't track much past the meridian because it runs into itself.

Total bonehead :smash: move for such an expensive mount.

Get a G11 or better instead of the CGE.

Suk

#7 jrcrilly

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Posted 07 March 2004 - 02:18 PM

If you end up getting a higher end german equatorial, I specifically would avoid the CGE. S&T reviewed it and found it can't track much past the meridian because it runs into itself.

Total bonehead :smash: move for such an expensive mount.

Get a G11 or better instead of the CGE.

Suk


Hi, Suk.

I don't think that's right; the CGE has switches so it doesn't run into itself. It just stops and waits to be told to flip. If I remember correctly, the G11 DOES run into itself and stalls because it has no switches. The only way to avoid this is to include automatic powered meridian flip, which means the mount will on its own and without warning slew 180 degrees. I don't want that to happen while I have cables dangling from the scope!

#8 Don W

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Posted 07 March 2004 - 04:35 PM

This is true with most GEM's.

#9 Suk Lee

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Posted 07 March 2004 - 07:33 PM

I don't think that's right; the CGE has switches so it doesn't run into itself. It just stops and waits to be told to flip. If I remember correctly, the G11 DOES run into itself and stalls because it has no switches. The only way to avoid this is to include automatic powered meridian flip, which means the mount will on its own and without warning slew 180 degrees. I don't want that to happen while I have cables dangling from the scope!


I mis-phrased: you're right, it has switches, however, it stops basically pointed at the Zenith. Total bummer if you're in the middle of a half hour exposure....

The Losmandys, Taks, Vixens, APs, Paramount, will image at least a couple of hours past the meridian. Usually some part of the OTA will contact the mount before the HEAD does. In the case of the Celestron, the HEAD is preventing the mount from going past the meridian.

Poor engineering like this really annoys me, particularly as Celestron is advertising that the mount is designed for astrophotography.

For example, on Astro-Physics mounts, if you slew to an object in the East, the mount will happily track past the meridian. You can specify a software stop that will prevent the mount from running the OTA into the pier. Now, if you track past the meridian and have the mount "upside down" and then tell the mount to GOTO the same objeft again, it WILL flip, but only because you've issued a new GOTO. Additionally, in case you DON'T want the mount to flip (because it changes your photographic composition), AP mounts have a "meridian flip delay" feature which let's you specify how many hours past the meridian to GOTO "upside down".

Point here is that somebody at Astro-Physics carefully thought through the needs of astrophotographers, as opposed to Celestron just claiming they did. Again, shame on such an expensive mount.

Cheers,
Suk

#10 jrcrilly

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Posted 07 March 2004 - 08:04 PM

Usually some part of the OTA will contact the mount before the HEAD does.


Well, if you're really sure that's a GOOD thing...
;)

I dunno. I like the failsafe aspect of it - but then I'm not much of an imager. I'm set up to do some remote imaging once the weather settles down and hope to keep crashes down to a minimum.


#11 Guest_**DONOTDELETE**_*

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Posted 07 March 2004 - 10:32 PM

I've followed the same idea as Steve for the most part. I bought a CG5-GT to use for a variety of reasons, but one is to do some basic imaging with an 80ED. I have on order a C9.25, but I'm not counting on it for astrophotography seeing as the OTA pushes the mount to its capacity.

So, I would go with the CG5-GT mount. You can use the difference in price to later fund a GM8/11 and use the CG5-GT for other scopes while your C9.25 is cooling down.

Just my opinion.

#12 Bob Pasken

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Posted 09 March 2004 - 11:10 AM

Quoting from page 61 of Sky & Telescope:

"One evening I was imaging Mars with a
webcam as the planet crossed the meridian
at 10:34 pm. A scant nine minutes later,
without warning, the mount reached its
limit and tracking abruptly stopped."

and later on page 61

"For examplem it is not possible to make a
40 minute exposure of any object that will
cross the meridian within 30-minutes of the
time you open the shutter."

As I read this, the objection is the LIMITED time you can image past the meridian. I read the limit to be 9 minutes past the meridian. Since all german mounts have the same problem, the only difference being how long can you can track why is this a FATAL flaw (ie. bonehead design) of the mount? I suspect that the AstroPhysics mount is significantly more expensive than the CGE and hence the reason why you can track "upside-down" If you are imaging with a CCD camera are you really taking exposures longer than nine minutes? I thought track-and-stack was the rule of thumb. If you are using a webcam for planetary imaging what's wrong with flipping the tube? Inquiring minds want to know



#13 Suk Lee

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Posted 09 March 2004 - 11:43 AM

I read the limit to be 9 minutes past the meridian. Since all german mounts have the same problem, the only difference being how long can you can track why is this a FATAL flaw (ie. bonehead design) of the mount?

OK, perhaps a little strong :jump:, it's not FATAL, possibly just really really ill ;)

I suspect that the AstroPhysics mount is significantly more expensive than the CGE and hence the reason why you can track "upside-down"

The Astro-Physics line *is* expensive, however, the quite reasonable Losmandy GM8 doesn't have this problem either. It's just poor design on Celestron's part, particularly given their enormous resources compared to a small company like AP. Given the large effort it takes to create a new mount, and a GOTO one to boot, it's a shame they didn't go the small further effort to make a really good mount. I wonder whether their tooling was committed and they didn't want to spend the $$$ to redesign. Kudos to S&T for not glossing over this problem.

If you are imaging with a CCD camera are you really taking exposures longer than nine minutes? I thought track-and-stack was the rule of thumb. If you are using a webcam for planetary imaging what's wrong with flipping the tube? Inquiring minds want to know

Yes, the individual shots are relatively short. The deal is that when you flip the mount, the OTA *rotates* with respect to the star field you're shooting. And the rotation isn't a simple 180 degrees, it depends where you're pointing in the sky. So, let's say you want to shoot an object that is available (because of twilight) at 1 hour East of the meridian and you want to shoot 3 hours worth (not an unusual amount of time for a DSO) i.e. you'd have to go 2 hours past the meridian. You compose your shot in twilight, get your mount calibrated, and start shooting. You get an hour's worth then hit the meridian stop.

OK, now you have to flip the mount, but before you do that, you'd better remember to take your flat-fields, because after you flip the mount, you're going to have to rotate your camera to get the same guide-star and composition.

OK, so you flip the mount. You now have to:
- rotate the camera re-find your guide-star and re-compose your photo
- recalibrate your mount because from the camera's viewpoint, the mount is now running "in the other direction"
- re-focus or at least check carefully, because you fiddled with the camera and any amount of fiddling is going to throw off critical CCD focus

The above is going to take around 30 minutes during prime shooting time when your object is overhead. Meanwhile, I'm tracking past the meridian with my AP900 and so is Ricky with his GM8, continuously shooting while the poor CGE user is going through all this extra work. Really fiddly pain-in-the-neck work. (Finding a guide star on an SBIG camera is a pain because the self-guide CCD is so small. The StarLight Express guys definitely have an edge in ease-of-use there.)

At the end of the second shooting session, you have to remember to take a second set of flat-fields otherwise you won't be able to calibrate your images and combine with the first set optimally.

I'm pretty negative on the Celestron mount for astrophotography because I feel (and so do a lot of others) that in a lot of ways, the mount is the most important component in an already hard-to-do/hard-to-learn activity. So, why buy this mount and set yourself up for all this extra work when you could buy a Losmandy G11 + Gemini for the same price?


Cheers,
Suk

#14 LivingNDixie

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Posted 09 March 2004 - 12:52 PM

The difference is the mounts, and a considerable price also..

Now, whats better for the use of astrophotography? The dual fork mount nexstar, or the German EQ mount on the "advanced" 9.25?

The dealer locally said he thinks the dual is better.. but most buffs here desire the german eq mount..

HELP! :confused: :tonofbricks:


Suk hits some really great points about the mounts. One thing I have noticed in the last few years, the big 2 (meade and celestron) are really trying to make products that sell. They are big corporations so they are stuck in that mindset. Companies like AP, Discovery, Stellarvue, Losmandy and others are owned by Astronomers so they tend to think more like astronomers...

Personally I think Meade currently is the worest about being a corporation and acting like a corporation. I think Celestron is trying to differentiate its self from Meade, and the new CGE line is one of those ways...

I have owned 2 Meades and now 1 Celestron (and a couple other companies). I'm very happy with my Nextstar. One thing you might want to do is match up a Celestron OTA to a Losmandy mount. I think for astrophoto taking and just regular viewing too that would be a sweet set up


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