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Old 12-05-2020, 07:53 PM
cken (Jack)
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Celestron cpc on wedge

Hi there,

I have an old CPC 1100 and a new Evolution Edge 8HD, both are on the AZ mount. So I bought a HD Pro Wedge and realise that only fit cpc1100.

Now I am trying to do astrophotography, a lots need to learn.

Can I post a pier at backyard and bolt the wedge on and use CPC11?
or Buy a EQ mount for Edge C8 HD?

Any suggestion would be really appreciated!

Jack
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Old 14-05-2020, 07:45 AM
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mental4astro (Alexander)
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Hi Jack,

To answer your questions, it's YES to both.

The only thing I can really add is, the CPC1100 is a very heavy rig - I'm not telling you anything new here. So, the question for you is will you be taking down the scope on the pier after every session? It becomes a question of safety for you and the scope.

Alternatively you could go the whole hog and build an obs with a pier. This way there is no need for taking down the scope. The CPC is then fixed in place. Then while the CPC is doing photo, you have your Evolution mounted scope to occupy your time with visual.

There's no right or wrong answer. Really it comes down to you, what you can physically handle, your home situation (yard, location, significant other, your place or rented, etc), and your expectations.

Now, if you would like ME to spend your money for you, and take no responsibility for it, hey, I'd be happy to!

Alex.
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Old 14-05-2020, 10:38 AM
cken (Jack)
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Hi Alex,

Thank you for your reply!

Yes, it's pretty heavy. I am tired after many years moving out and back from garage to backyard.

That 's one reason I am thing to get a pier.
My concern is if the wedge is accurate for the long exposure?

Another question is comparing older C11 and new C8 HD, which one is better for image?

Many thanks!
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Old 14-05-2020, 11:14 AM
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mental4astro (Alexander)
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Hi Jack,

The answer to your question is, as always, it depends...

Now, both scopes are a native f/10. That as such is not really an issue with today's astro cameras. The physical difference between the two scopes is the Edge has a built in field flattener. What this means is if you use a camera with a large chip size (not talking pixels, but the actual size of the sensor), an image taken with the Edge scope the edges and especially the far corners of the pic all the stars will be nice and sharp. In the standard SCT like your 11", the stars will start bloating out because of the effects of coma this scope design had inherent to it.

This is not fatal, and there is a simple solution for your 11" - using an f/6.3 focal reducer-corrector will eliminate the effects of coma plus give you a faster focal ratio of f/6.3

If you use a camera with a small chip, you may not see any coma in the pics with the 11". But you will be using the full focal length of the scope.

There is also a focal reducer for the Edge scopes, but it is not the same lens as used for the standard SCT.

As for the wedge, i cannot say. It certainly is a robust bit of kit, and I am sure many people are happily using one. For many purposes it most likely will be just fine, with the greatest source of problem being alignment accuracy, as with any eq mount too.

As you would know, each scope has its own appeal, pros and cons. It's not for me to tell you what you MUST do, just explain the ins and outs of each.

I hope this helps.

Other people may have other thoughts too.

Alex.
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Old 14-05-2020, 12:52 PM
cken (Jack)
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Many thanks for your warmly help.

I have both reducer, one f6.3 for CPC 1100 and 0.7 for edge 8. Is that means C 11 + F6.3 = EDGE 11?
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Old 14-05-2020, 01:58 PM
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mental4astro (Alexander)
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Quote:
Originally Posted by cken View Post
Is that means C 11 + F6.3 = EDGE 11?
No.

It means that the effective focal length is 1764mm, and the focal plane is now flat across the whole field.

The Edge 11 has a flat focal plane from the very start at its native focal length of 2800mm.

I know how confusing it can get. Best to think of the Edge scopes and the standard SCT's as two totally different systems, each with its own set of optical features/differences. They look similar, but that's where the similarities end. Much in the same way as with Maksutovs, RC's and Dall Kirkhams - these are also all Cassegrain telescopes, but all make use of different design variations and all have their own photo accessories that are not interchangeable (except for barlow lenses).
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Old 14-05-2020, 08:10 PM
cken (Jack)
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Understand, thank you so much
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Old 17-05-2020, 05:45 PM
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Sunfish (Ray)
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An SCT works well on a wedge on a pier. A pier top plate I use has three holes in a 12 mm thick alloy plate 200 diameter to take the wedge. It is countersunk bolted on to an 80 mm diameter solid aluminium bar 200 long and another matching plate which has holes to to take the fork without the wedge when reversed. The 80 mm bar gives access to the back of the plates for bolting with butterfly nuts . It was made by a scientist friend in his workshop for the SCT and bolts to a welded plate on top of the CHS pier .

It is quite heavy loading the SCT and fork on the wedge so do not make the plate too high and use a safe platform. I imagine a c11 would require some help lifting but the fork on the wedge can stand balanced until bolted so perhaps a matching loading table would help.
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Old 17-05-2020, 08:33 PM
cken (Jack)
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Quote:
Originally Posted by Sunfish View Post
An SCT works well on a wedge on a pier. A pier top plate I use has three holes in a 12 mm thick alloy plate 200 diameter to take the wedge. It is countersunk bolted on to an 80 mm diameter solid aluminium bar 200 long and another matching plate which has holes to to take the fork without the wedge when reversed. The 80 mm bar gives access to the back of the plates for bolting with butterfly nuts . It was made by a scientist friend in his workshop for the SCT and bolts to a welded plate on top of the CHS pier .

It is quite heavy loading the SCT and fork on the wedge so do not make the plate too high and use a safe platform. I imagine a c11 would require some help lifting but the fork on the wedge can stand balanced until bolted so perhaps a matching loading table would help.
.

Wish I could have this friend
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