How to Mount a Guidescope on a C8?

Matty P (Matt) · #1 10-02-2008, 12:22 PM

Now that I have caught the Astrophotography bug (again)

. I have decided it is time to attempt to piggyback my refractor on top of my Celestron 8" SCT as a guide scope, although the EQ6 won’t be arriving for some time.

I need some advice on what is the best way to do this because I have no clue.

Thanks

Matty P (Matt) · #2 10-02-2008, 12:31 PM

Here are details of the Guide Scope:

Bushmaster F500 Refractor OTA

Lens: 50mm multi-coated achromatic objective lens, f/7
Focal Length: 700mm
Weight: 1.2kg (Estimate)

Will this be a suitable guide scope?

JohnG (John) · #3 10-02-2008, 12:57 PM

Hi

There are a couple of ways you can go about mounting a guidescope to a C8. You can go side by side or you can mount the guidescope on the OTA itself. You will need to take into account the rigidity of the system and how you actually mount the guidescope itself. The most common way of mounting the guidescope is by use of adjustable rings, these allow you to move the guidescope around to center a suitable star on which to guide.

Side by side setup like this will work although you will have to get the required dovetail plate:

http://www.starstuff.com.au/index.html or

http://www.astro.premcom.com/ADM/ADM...ducts/DSBS.htm

Piggy back style, you can either go 4" using Losmandy or similar plates, using the ADM mini system or the new Losmandy "V" Series.

http://www.astro.premcom.com/ADM/ADM...escription.htm

http://www.losmandy.com/v-series.html

http://www.losmandy.com/secondary.html

Or possibly make your own.....just remember that it has to be rigid.

Cheers

Matty P (Matt) · #4 10-02-2008, 04:37 PM

Thanks John,

I think piggybacking the refractor on the OTA is a better option as far as I am concerned.

I am still a bit lost on how I will mount the brackets on the OTA.

Thanks

Zuts · #5 10-02-2008, 04:42 PM

Quote:

Originally Posted by Matty P

Thanks John,

I think piggybacking the refractor on the OTA is a better option as far as I am concerned.

I am still a bit lost on how I will mount the brackets on the OTA.

Thanks

Matty P

Your C8 has a number of small screws around the top and bottom edges. These are designed to be removed. Losmandy and other companies sell dovetail plates and radius blocks which can be fitted to these holes.

Basically remove the screws and fit radius blocks on each end, fit a dovetail the full length of the tube attaching to the radius blocks and the tube rings attach to this.

http://www.optcorp.com/productList.aspx

Without getting into any arguments, Losmandy make the best (and most expensive) fittings but there are other options.

Paul

JohnG (John) · #6 10-02-2008, 05:11 PM

You won't get any arguement out of me

, ADM come a close second and are very easy to deal with.

Cheers

Zuts · #7 10-02-2008, 05:13 PM

Quote:

Originally Posted by JohnG

You won't get any arguement out of me

, ADM come a close second and are very easy to deal with.

Cheers

Wow Cootamundra,

I envy your soon to be dark skies

JohnG (John) · #8 10-02-2008, 05:21 PM

About 4 weeks

, gotta re-assemble everything

.

Got to be better than down here on the Far South Coast, haven't imaged in over 4 months.

Cheers

h0ughy (David) · #9 10-02-2008, 05:21 PM

http://www.iceinspace.com.au/forum/a...4&d=1186955452 look at the scope on the right, althoug th scope on the left is similar. The guy in the middle has no known adapter (sorry Al)lol

JohnG (John) · #10 10-02-2008, 05:28 PM

A closeup of the ADM mini system with 125mm Guiderings.

Seen that scope before, Dave

Cheers

Matty P (Matt) · #11 10-02-2008, 05:29 PM

Thanks guys,

I have attached different pictures of the C8 OTA. I was just wondering, when I mount the OTA on the EQ6. The OTA will be on its side... is that OK?

Can you please let me know which screws that can removed and the ones that can't. I don't want to remove any that hold something important inside the OTA.
It won't be a pleasant experience.

JohnG (John) · #12 10-02-2008, 05:39 PM

Hi

OK, in your pictures, the real Top and Bottom are the left and right side pictures, the top is identified by where the reflex finder is located.

To put a Dovetail plate on the OTA, you will need to remove single screw on the front of the OTA and the 2 screws on the rear casting, you remove the same three screws on the top of the OTA to attach the upper dovetail plate.

Normally when you put an after market dovetail on the OTA, you will get 2 radius blocks, the rear block has 2 longer screws which are normally supplied, they hold the Radius Block to the OTA, the front is held by a long screw which goes through both the rail and the radius block.

Hope that helps.

Cheers

JohnG (John) · #13 10-02-2008, 05:43 PM

In addition, the right hand photo is the top, you can identify it by the extra 2 screws to the lower side of the center, these are for the 7 x 50 finderscope.

Cheers

Matty P (Matt) · #14 10-02-2008, 05:50 PM

Thanks John,

Are you talking about these screws to remove?

JohnG (John) · #15 10-02-2008, 05:54 PM

Yep, that's them

, for the bottom you remove the corresponding 3 screws, 180 degrees away.

Cheers

Matty P (Matt) · #16 10-02-2008, 06:03 PM

Thanks for your help John.

So all I need is a Dovetail Bar for a Celestron C8 + radius blocks (see attachment) and some Guide rings for the Guidescope and I should be up and running.

JohnG (John) · #17 10-02-2008, 06:15 PM

You got it

.

Make sure you measure the tube diameter of your guidescope and get the right sized rings, you need to make sure they will fit over the objective.

Glad to be of help.

Cheers

Zuts · #18 10-02-2008, 06:36 PM

Just a thought,

I think a 50mm is a bit small as a guide scope. I would get at least a 70mm achro. There cant be much difference in price.

Paul

Matty P (Matt) · #19 10-02-2008, 06:51 PM

Quote:

Originally Posted by Zuts

Just a thought,

I think a 50mm is a bit small as a guide scope. I would get at least a 70mm achro. There cant be much difference in price.

Paul

I was just thinking about that...

The weird thing is that the numbers don't add up.

If it was 50mm refractor with a focal length of 700mm, that would make it an F/14 scope, not F/7.

The main problem is that I don't have the scope here ATM so I can't get the exact dimensions.

I think it is a 70mm or 80mm refractor.

JohnG (John) · #20 10-02-2008, 07:03 PM

f/14-15 is not unusual for a refractor, was how they coped with the excessive colour in the image.

I would suggest around an 80mm/f/7 or thereabouts.

I dont use a guidescope anymore because of the duel chip in the ST4K but I have provision on the TSA-102 to carry a guidescope, an 80mm SW ED Pro when I use the DSLR.

My field setup with the GM-8 is the SW ED80 Pro with a WO 66SD as the guidescope, using a Q-Guider as an autoguider and the DSLR on the 80mm, makes for an excellent widefield setup.

Cheers