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How to take images with C8?

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#1 betelgeuse91

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Posted 27 March 2020 - 01:32 AM

Hi, I have been imaging with a refractor and a dslr, and recently I am considering getting an old C8. 

 

What do I need to image with it?

 

Do I need to get a crayford focuser?

 

I am going to guide with a guidescope for now, if I get one.

 

Also, is there a way to use 2" filter?

 

Thanks!


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#2 khobar

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Posted 27 March 2020 - 02:43 AM

I use a C8 for imaging at times. You could get a Crayford to potentially elimimate focus shift, but keep in mind it will add a fair amount of weight to the back end. I have one. Wife bought it for me but I've not used it due to weight. If you have a beefy enough mount, might work, but you *may* also have to add a SCT counter weight to the front - something like this perhaps: https://www.buyteles...il-clamp-174487

Or just make sure with the existing focuser and be prepared.

 

Bahtinov mask - essential for focus.

 

To use 2" filter - get a 2" visual back and a 2" t-thread adapter (such as: https://www.telescop...r/p/113926.uts)

 

Your DSLR can then attach to that adapter. Or, if you are using a CMOS camera that normally would slide into a 1.25" EP socket, you can get one of these: https://www.amazon.c...85294781&sr=8-9

 

I would also suggest checking astrobin.com and see what people do with C8's.

 

Good luck and clearer skies than I'm having right now. :) :) :)


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#3 einarin

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Posted 27 March 2020 - 02:53 AM

What mount do you have ?

EQ5 Pro (Sirius) mount is absolute minimum for it.

And I recommend using a focal reducer with it.


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#4 WadeH237

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Posted 27 March 2020 - 10:15 AM

I image with an EdgeHD 8.  Here is what I consider to be the minimum to image with an 8" SCT:

 

  • A good mount.  I would suggest that the minimum would be an EQ-6.
  • A FeatherTouch focus knob with a focus motor (or equivalent).  I would not recommend a Crayford focuser for two reasons.  First, it will do nothing to prevent mirror flop, which is the real beast when imaging with an SCT.  And second, it will add to the backfocus, which will both increase the focal length and be less than optimum for spherical aberration correction.
  • An OAG.  I know that you want to avoid this, but in my experience it is simply not an optional thing.  You *will* get significant flexure without one.  On my EdgeHD 8 with a guide scope, I get very noticeable star elongation at 3 minutes, with completely (to me) useless subs at 5 minutes, and this is with the EdgeHD mirror clutches locked.
  • Consider a focal reducer (in the case of a standard SCT, you'd want the Celestron F/6.3 reducer/corrector).

To be clear, nothing prevents you from putting an 8" SCT on a small mount, attaching a camera and guide scope and giving it a try.  You should be able to get some results doing that.  But from experience, I can tell you that if you are like me, you will quickly run into the limitations of such a system.  My suggestions above are what I consider a minimum list of requirements to get past those limitations.


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#5 betelgeuse91

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Posted 27 March 2020 - 11:45 AM

Thank you all for the advice. I have an AVX which I modded and had a bit of confidence in guiding. But it looks like it'll be far more complicated than I thought...

 

If guiding could not work for an EdgeHD, an OAG would be necessary for me... 

 

Focuser, OAG, and dealing with the weight shifting... I will look into those. Thanks everyone again.!




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