How to Mount a Guidescope on a C8?

[Matty P]

Now that I have caught the Astrophotography bug (again):whistle:. 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 :thumbsup:

[Matty P]

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]

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%20Products/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%20Products/MDS%20Description.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]

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 :thumbsup:

[Zuts]

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]

You won't get any arguement out of me :), ADM come a close second and are very easy to deal with.

Cheers

[Zuts]

Wow Cootamundra,

I envy your soon to be dark skies :)

[JohnG]

About 4 weeks ;), gotta re-assemble everything :lol:.

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

Cheers

[h0ughy]

http://www.iceinspace.com.au/forum/attachment.php?attachmentid=30424&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:lol:

[JohnG]

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

Seen that scope before, Dave :lol:

Cheers

[Matty P]

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. :scared:

:thumbsup:

[JohnG]

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]

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]

Thanks John,

Are you talking about these screws to remove?

[JohnG]

Yep, that's them :thumbsup:, for the bottom you remove the corresponding 3 screws, 180 degrees away.

Cheers

[Matty P]

Thanks for your help John. :thumbsup:

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]

You got it :thumbsup:.

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]

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]

I was just thinking about that... :doh:

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

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. :doh:

[JohnG]

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

[Zuts]

One other thought. If you got an ED80 ($499) from Andrews then you would have a great guide scope. Also you could switch and guide through the C8 and image through the ED80.

Paul

[Matty P]

I might consider getting an ED80 for a GS and a imaging scope. Thanks for the suggestion. :confuse3:

I was just wondering...

How will I use my C8 as a Guidescope? Do I just switch around the cameras so one is imaging the object and the other is guiding on a star? :shrug:

[Zuts]

Yes,

Just switch the roles of the scopes. This way you can get some nice widefield from the ED80, i think 600 mm FL and less with a field flattener (or people have also used the WO 66) and around 1200 mm with a .63 reducer on the C8.

When you are just starting out you will find the FL of the ED80 much less demanding of really good polar alignment than the C8. Basically it is better to start the learning process at a shorter FL.

When I started out i was trying to image through a C11 at 2700 mm, eventually i gave up...When my skills improve I will try again :)

Paul

[JohnG]

If you are going to get an ED80, make sure it is the ED80 Pro, it has the FPL53 glass and is a fine wide field imaging instrument.

A couple of shots using the SW ED80 Pro:

http://www.pbase.com/takman2/ed80_photos

I have yet to use the WO Flat 2, reducer with this scope as I have found the field quite flat, see the full frame shots.

Cheers

[Matty P]

I have decided to get the Losmandy Dovetail Plate from Bintel to mount the guidescope.

Just a question.

If I get the ED80 and because it will be mounted on top of the C8. Can I use the ED80 to image whilst mounted on top of the C8? or will I have to remove it?

[Zuts]

Hi,

If you removed it then you wouldnt have a guide scope.

It would be far more stable without the C8, but the EQ6 should be able to handle the C8 and the ED80. So try guiding through the C8 and imaging through the ED80.

Paul