Skywatcher ST80 as guidescope for C9.25

[Jammy]

This question has probably been answered a dozen times, but I haven't found the answer either here or on the manufacturers website.

Does anybody know the physical dimensions of a Skywatcher ST80 telescope?

I'm thinking of getting one to use as a guidescope for my C9.25, and don't really want a guidescope thats going to be longer than the main scope.

Also, can you tell me what size tube rings this scope will need for attaching it?

I've seen the ADM mini dovetail system for attaching the scope on the FLO webiste.  Are there any better ways of attaching a guidescope to an C9.25 telescope?

Many thanks for your assistance.

[jgs001]

The ST80 is a 400mm focal length scope, it needs 90mm tube rings. Actually, it looks like it comes with a set of rings...

http://www.firstlightoptics.com/startravel/skywatcher-startravel-80-ota.html

[Jammy]

Thanks for the reply. I've seen the focal length given on various websites, but would like to know what the actual overall length is. Does anyone have an ST 80 and a tape measure?

[jgs001]

Mine is buried in a case, and I can't easily get at it. However the case is 450mm (Maplin flight case). Ok the focusser is fully retracted, and to reach focus with a guidecam you do need an extention tube or two (30mm added at least) that should give a close approximation. Mine is a Konus Vista80s, but it's the same scope.

[Uplooker]

390L x 110 mm at its widest.

Ian

[Jammy]

Many thanks for your help  

[Patrice Lanteigne]

Thanks for the reply. I've seen the focal length given on various websites, but would like to know what the actual overall length is. Does anyone have an ST 80 and a tape measure?

As shown in the photo, mounted on an 8" SCT, the length is 440 mm from the end of the diagonal to the end of the dew shield.  The outside diameter of the dew shield is 100 mm.

[Jammy]

Looks a great setup How have you attached the guidescope Pat? I can't see any tube rings in the photo, but I am looking at a tiny photo on my phone!

[r3i]

Just to throw a spanner in the works, you might want to consider an OAG, which should give you a better guiding performance with the long focal length of the C9.25.

[Jammy]

Just to throw a spanner in the works, you might want to consider an OAG, which should give you a better guiding performance with the long focal length of the C9.25.

I've seen other posts on this forum saying that you should avoid OAG with the C9.25 because of the long focal length, unless I'm mistaken?

I'm totally confused now

I've recently bought a f6.3 focal reducer and want to try my hand at imaging with a DSLR.  I don't have a guide camera and guide scope as yet.  I'm still open to suggestions as to the best way forward.

When I've exhausted the DSLR option I may move onto a dedicated CCD camera, but that's some way off.

All guiding suggestions greatly received

[ollypenrice]

People do use guidescopes with SCTs but I use ST80s for guiding our refractors and an OAG for guiding Yves' resident 14 inch Dall Kirkham (similar to an SCT.) I would consider the OAG a far safer bet since you have a long focal length which must be kept to sub pixel errors if you are to exploit the theoretical resolution of your optics. Round stars do not define sub pixel tracking accuracy. They may arise from a randomly distributed set of small guiding errors.

Olly

[Mav359]

I have an C9.25 and use a QHY5+9x50Finderscope as my guider and it works a treat, cheaper as well i'd assume. Heres a pic of mine

[Patrice Lanteigne]

Looks a great setup How have you attached the guidescope Pat? I can't see any tube rings in the photo, but I am looking at a tiny photo on my phone!

My SW 80mm came with a system to bolt directly to the mount as in the attached photo. I attached a vixen clamp to the scope which mounts onto the vixen dovetail on top of the SCT. The clamp is a short ADM style removed from a Duo-T mount upgraded to dual ADM DV clamps.

[r3i]

I've seen other posts on this forum saying that you should avoid OAG with the C9.25 because of the long focal length, unless I'm mistaken?

I'm totally confused now

Can you give a link to these posts as long focal lengths is where an OAG comes into its own.  It also helps to address problems with SCT mirror flop.

[Jammy]

As I said, it's probably my misunderstanding.

I can see how it could help, especially now that you have mentioned SCT mirror flop.

Do off-axis guiders differ for using DSLRS and CCD cameras?  I mean the fitting of the image camera, not the guide camera.

I need to read up on this I guess.

[r3i]

Quite a few threads on this forum about OAGs, here's a few that I could find which might be of interest:

http://stargazerslounge.com/topic/120844-cant-find-a-guide-star-with-my-oag/

http://stargazerslounge.com/topic/143184-help-oag-at-2800mm-focal-length/

http://stargazerslounge.com/topic/172120-oag-vs-guide-scope/

http://stargazerslounge.com/topic/175022-which-oag-for-sct-please/

[Jammy]

Quite a few threads on this forum about OAGs, here's a few that I could find which might be of interest:

http://stargazerslounge.com/topic/120844-cant-find-a-guide-star-with-my-oag/

http://stargazerslounge.com/topic/143184-help-oag-at-2800mm-focal-length/

http://stargazerslounge.com/topic/172120-oag-vs-guide-scope/

http://stargazerslounge.com/topic/175022-which-oag-for-sct-please/

Thanks again Mike.  I've been reading a few threads and trying to learn more about OAG.  I'll have a look through your suggested threads, and will no doubt come back with a stack more questions.  Sorry in advance!