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Wedge for CPC925

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#1 WilliamAlexander

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Posted 30 March 2009 - 01:02 PM

I am really new to this great site so forgive me if I posted this in the wrong place.

I have been considering purchasing an equatorial wedge for my CPC925. Can anyone tell me what to expect? What I mean is, will the telescope perform well at what will seem (to me, anyway) to be an odd angle for the way it is designed? Are there any weight issues? Etc. etc. .. In other words I don't want to blow the $$$ for the wedge if the scope will be wonky with it.

My reason for doing this is, of course, photography...

I would love to see a photograph of an EQ mounted CPC, if anyone has one.

Thanks,

-W

#2 mclewis1

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Posted 30 March 2009 - 02:48 PM

The Celestron heavy duty wedge is not generally recommended for the C9.25 and C11. Mitty, APT, and a few others are 3rd party wedges that are heavy enough to handle a scope like the CPC925. They are however expensive (as much as $700). Mounting a C925 on a wedge each night is no picnic ... you have to angle the base of the scope to match the wedge and then get one of the bolts in place before you can let it go.

Most folks with wedges have them on a permanent pier of some form, this helps with stability and in may cases the scope is also left on the mount so there is no setup to do.

There aren't too many fork mounted CPCs ... most folks move to a GEM when they get serious about AP. If I had a CPC and really wanted to get into AP (as opposed to casual interest) I'd consider selling the whole CPC and purchasing a CGEM925. I think you could get $1700 for the CPC, a new CGEM925 is only $1000 more. A wedge will be up to $700 so for $300 you're getting a better AP platform. You will loose some of the convenience of the CPC for visual work but you'll gain much more on the AP side.

#3 mish

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Posted 30 March 2009 - 06:30 PM

I have been considering purchasing an equatorial wedge for my CPC925. Can anyone tell me what to expect? What I mean is, will the telescope perform well at what will seem (to me, anyway) to be an odd angle for the way it is designed?


The Celestron heavy-duty fork works fine for this... and the angle is odd only if you're used to alt-azimuth mounts (it's easy to assert that anything but an equatorial mount is odd, though, so it depends on what you're used to).

Putting the scope on the mount isn't really difficult, but it can be exciting the first few times -- I'd recommend practicing this in the house, with spotters present just in case. Most Celestrons have three bolts for attachment to the wedge, and if the one at the top of the mount is threaded just enough to get a grip, it's easy to slide that one into the slot on the wedge, and that will hold the telescope while you fiddle with the other two.

I bought slightly longer screws for this, and then put wingnuts on them so I could screw them enough by hand to seat them firmly, and then crank down the wingnuts to provide sound attachment to the wedge. It's pretty easy getting all three screws well-seated, and then everything just works.

The heavy-duty wedge places the telescope's center of mass reasonably well over the center of the tripod, so unless your tripod is flimsy, the whole thing works out very well. Spending a bit of time beforehand getting the latitude set properly and getting the thing pointed north helps a lot. If you have a lot of weight spread around the tube (e.g., a heavy finder), you'll likely need to add a counterweight system -- I use a Losmandy version made for the Celestrons, and it works great.

#4 mclewis1

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Posted 30 March 2009 - 08:20 PM

I'd search CN and the web in general for "Celestron wedge" and draw your own conclusions about how appropriate the Celestron HD wedge is with the NexStar/CPC 925/1100 scopes (they use the same forks and base and the OTAs are within a few pounds of each other). You will however find less issues with folks using the lighter weight NexStar/CPC800 scopes.

#5 jrcrilly

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Posted 30 March 2009 - 08:30 PM

Can anyone tell me what to expect? What I mean is, will the telescope perform well at what will seem (to me, anyway) to be an odd angle for the way it is designed?


It depends a lot on your latitude. The lower your latitude, the greater the variation from the attitude for which the mount was designed. Better wedges are easier to adjust (and that's plenty of reason to prefer a better unit), but most are plenty stable in themselves. The instability issues tend to come from the fork arms, which are suddenly side-loaded rather than simply acting as vertical support columns. I'm at 41 degrees N and have had good success with wedge setups that others, farther South, have found to be unusable due to fork arm flexure.

#6 nhraj700

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Posted 30 March 2009 - 09:10 PM

farther South, have found to be unusable due to fork arm flexure.


Do you know how much farther south? I am considering the same and am at 38°54'. Is this going to pose any issues?

Does anyone have a basic formula to plug in using your latitude that gives you an idea of the angle of the wedge? Maybe that's simplifying it too much??

#7 mish

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Posted 30 March 2009 - 09:21 PM

Do you know how much farther south? I am considering the same and am at 38°54'. Is this going to pose any issues?


I'm at 35 degrees, and the heavy-duty wedge works great with a C8, even for some prime-focus astrophotography, and it works alright for visual observation with a 53-pound U11 (tho I would definitely not recommend astrophotography with that thing).


Does anyone have a basic formula to plug in using your latitude that gives you an idea of the angle of the wedge? Maybe that's simplifying it too much??


90 degrees minus your latitude gives the angle the wedge makes with the horizontal plane.

#8 jrcrilly

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Posted 30 March 2009 - 09:37 PM

farther South, have found to be unusable due to fork arm flexure.


Do you know how much farther south? I am considering the same and am at 38°54'. Is this going to pose any issues?


38 degrees shouldn't be much of a problem; that's close to my 41 degrees. It's the folks down around 25-30 degrees who seem to have issues.

#9 bookworm14

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Posted 01 April 2009 - 08:31 AM

I was also considering buying a wedge or moving to a GEM mount for my Celestron CPC 1100. Then I discovered the Hyperstar system. I haven't bought one yet, but the very short exposure times on the f/2 Hyperstar apparently obviate the need for a wedge or GEM.
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