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solutions for 8SE to make long exposure possible

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#1 M16SEAL

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Posted 18 August 2012 - 11:55 PM

I have celestron 8 SE with Alt-azm mount and I want to take long exposure astrophotagrphy ...what should I do to make long exposure possible , to get celestron wedge HD or to get CG-5 equatorial mount .

#2 frolinmod

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Posted 19 August 2012 - 01:39 AM

If those were my only choices, then I'd go with the CG-5. Better yet, get a "Orion Atlas EQ-G" or "Sky-Watcher EQ-6 Synscan" mount. These are the same mount. The 8SE OTA is a fairly good match for that mount. When it comes to astrophotography, the mount is the most important ingredient.

#3 RTLR 12

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Posted 19 August 2012 - 02:15 AM

M16SEAL,

Get the CG-5 mount or CGEM if you can afford it. The SE mount just isn't up to the task of AP and the use of a wedge won't improve on that fact. The CG-5 will have firmware you are familiar with and it is a good progression from the SE mount.

Stan

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#4 Midnight Dan

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Posted 19 August 2012 - 09:33 AM

Hi M16SEAL:

The 8SE is on an Alt/Az mount which means that exposures over 20-30 seconds will show field rotation. You can add a wedge as you suggested to get around that limitations, but the mount also has spur gears with lots of backlash which also limits your exposures times to about the same range. Bottom line, a wedge will not improve your ability to do long exposures on this mount.

A CG-5 is a much better option, but is considered an entry level mount for AP (astrophotography). While there are those who use it with a C8, it is better suited to shorter focal length scopes. You would have much better results with a mount like an Atlas, CGEM, or iEQ45. Of course those cost considerably more too.

-Dan

#5 M16SEAL

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Posted 19 August 2012 - 03:41 PM

So .. It's better to get CG-5 , but what's different between CG-5 & CGEM

#6 psu_13

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Posted 19 August 2012 - 05:06 PM

CGEM is bigger and heavier.

#7 frolinmod

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Posted 19 August 2012 - 05:11 PM

Yup. The CGEM is roughly comparable to the Atlas / EQ-6.

#8 Falcon-

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Posted 19 August 2012 - 07:37 PM

CGEM is bigger and heavier.


More importantly the bigger/heavier CGEM (or Atlas or EQ6 or iEQ45) is better able to give precision tracking & autoguiding at longer focal lengths and with heavier telescopes.

I use a CG-5 myself and I agree with what others said. A C8 on a CG5 is right on the edge of the mount's capabilities - not impossible, just a bit harder to get REALLY long exposures out of (like 5 & 10 minutes long). With the focal length of the C8 reduced to 1280mm using an f/6.3 reducer-corrector it is a bit easier so you should consider that a highly recommended addition.

So if money is tight get a CG-5 and a f/6.3 reducer-corrector for your 8SE. If you can afford it get a CGEM-class mount (and f/6.3 reducer/corrector) then you will have a slightly easier time of it and will know the mount is more capable of advanced AP down the road.

Either way, have fun with it! :)

#9 Falcon-

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Posted 19 August 2012 - 07:40 PM

Oh, and BTW, no matter what mount you get (including the wedge option) do not forget to do some wide-field imaging using just camera lenses alone - LOTS of great targets to be shot that way and it is a lot easier to do since it is less sensitive to minor tracking/guiding/alignment problems.

#10 Peter D.

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Posted 20 August 2012 - 10:39 AM

I'm working on the same issue myself: I'm interested in AP, but I've given up on my C8 (with its long focal length, jiggly spur drive and flexible wedge). I'm now using a CG5-GT (which I like very much for its excellent firmware and go-to accuracy at a very reasonable cost), but I've found that its periodic error is too erratic for optimal guiding and hopeless for non-guided AP. So I'm looking for an upgrade path that's not too expensive. I had considered the CGEM, Atlas, and iEQ45. The iEQ45 looks great on paper and in reviews, but I haven't heard any astrophotographers raving about its performance. From my conversations at Stellafane this past weekend I've come to understand that the Atlas and the CGEM are identical mechanically, made in the same factory to the same quality standards. Besides physical appearance, their only differences are the electrical interconnections and firmware. Since I'm most familiar and satisfied with the excellent CG5 firmware, that would appear to be the best path for me.

Although the AP'ers I met at Stellafane agreed that the Atlas/CGEM would be an effective upgrade from the CG5 they universally recommended a used Losmandy G11 or Celestron CGE. These are a big step up in size, capacity and quality, at a cost only slightly higher than even a used Atlas or CGEM. Reportedly the G11 and CGE may be obtained used for around $1500, but I haven't found any bargains like that yet. Welcome to the crazy world of AP.

#11 frolinmod

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Posted 20 August 2012 - 02:58 PM

Welcome to the crazy world of AP.

Don't you know it. I've seen an EdgeHD 8 OTA mounted on a Paramount MX. It looked perfectly happy there too.






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