advice on attaching my guidescope to my main scope and threadsize please

[studio1one]

Hi,

I thought I would ask a question because literally i am making this up as I go along!!

Hopefully I am not doing things a totally screwy way but I am not sure. Anyway I have a pictorial of what I am doing.

First here is my guide OTA

sorry ignore the paperwork and mess

and here is how I intend to attach my OTA to a mini dovetail

and then I intend to screw it onto my main OTA via the central thread in my mini dovetail like so

OK so assuming all the above is sensible does anyone know what this thread size is on the rings on the ST80 because I don't seem to have any bolts here that will fit

Thanks in advance for any help and advice.

[studio1one]

ummmm except obviously in the 3rd pic the mini dovetail is upside down to the way it would be

[studio1one]

Ok so for accuracy's sake I would actually be attaching the dovetail like this, but with the OTA on it

[Merlin66]

It will work...but not very well....sorry.

Attaching the guide scope via the dovetail to only one ring will not be stable enough for the challenge...

I've suggested in the past to use a bit of 25 x 12 Aluminium channel across the tube rings then fit the guide rings to that. Much more stable and rigid.

Just my 0.02 euro

[studio1one]

thanks Merlin, any Euro welcome no matter how small the denomination

[carastro]

As stated above you need the guidescope to be very stable as any movement will affect the guiding, plus as an extra tip, you need to secure your cables so they don't flap around as this can do the same thing.

My one comment on your planned set up (on two mounting rings) is it will work provided there is a guide star in the FOV, so much depends on the sensitivity of the guide scope you are planning to use. However even with a sensitive guide scope (i.e. QHY5 which I use), there are times when I cannot find a guide star, so what are you going to do then? Move the object to be imaged to one side of the frame?

The best thing is to get guide rings for the guidescope rather than the mounting rings you currently have. These have 3 adjustment screws (like a finderscope), so you can adjust your guidescope until you can find a suitable guidestar.

Hope this helps.

Carole

[studio1one]

OK Merlin,

just to be clear. If I bought a length of Aluminium, drilled it where my tube rings are on my OTA and then two more holes where the tube rings are on the guidescope would the black large washer disk shown in the image below be enough to bolt the aluminium down (one on each ring obviously) onto the main OTA?

also do you know the thread size on the rings on the ST80? I can try trial and error but it seems a bit of a waste of cash.

Thanks for your input, it really is appreciated.

[Veracocha]

Standard 33cm skywatcher dovetail spanning both rings, around £20.00

[studio1one]

As stated above you need the guidescope to be very stable as any movement will affect the guiding, plus as an extra tip, you need to secure your cables so they don't flap around as this can do the same thing.

My one comment on your planned set up (on two mounting rings) is it will work provided there is a guide star in the FOV, so much depends on the sensitivity of the guide scope you are planning to use. However even with a sensitive guide scope (i.e. QHY5 which I use), there are times when I cannot find a guide star, so what are you going to do then? Move the object to be imaged to one side of the frame?

The best thing is to get guide rings for the guidescope rather than the mounting rings you currently have. These have 3 adjustment screws (like a finderscope), so you can adjust your guidescope until you can find a suitable guidestar.

Hope this helps.

Carole

Thanks Carole, I know I could do with some guiderings really but I'm a cheapskate!!!!!

I was thinking if I had a length of aluminium aluminium I could drill long, rather than round holes and loosen the guidescope to let it slide a bit to find a star before tightening.

If I was to do it as the image in my first post I could easily move the large washer disk up and down to change the tight position of the guidescope and therefore have off axis guiding.

[studio1one]

Standard 33cm skywatcher dovetail spanning both rings, around £20.00

Doh,

I am such a retard, I have one sat in the shed.

[Merlin66]

The bolts with the "large black washer" are 1/4" unc - to fit a piggy back camera...the holes in the rings usually fit the M6 threaded holes in the dovetail....

Before you drill any holes for the guide scope - check the best balance position!!

[studio1one]

Ok final thing now I promise, I just need the size of the thread on the inner holes of the standard dovetail (which look like and I assume are, the same size as the ones on the rings of the ST80 as above).

[studio1one]

The bolts with the "large black washer" are 1/4" unc - to fit a piggy back camera...the holes in the rings usually fit the M6 threaded holes in the dovetail....

Before you drill any holes for the guide scope - check the best balance position!!

Ha, you posted that just as I posted my last post. 2 x M6 bolts and I am away.

Thank you all much much appreciation coming from me here.

[Veracocha]

I was thinking if I had a length of aluminium aluminium I could drill long, rather than round holes and loosen the guidescope to let it slide a bit to find a star before tightening.

I did this on the rear hole only so I could pivot the guidescope 10mm either way.

[studio1one]

How does it work for you?

[Veracocha]

So far the ST80 has had no trouble finding a suitable star so I have yet to put it into practise.

[studio1one]

Thanks to everyone for all your help on this, particularly Veracocha for pointing out what was sat right in front of me (a battered old dovetail in the shed). I went out and bought a couple of M6 bolts and hey presto. While the thread on the dovetail is unquestionably M6, my god it is machined within a tight tolerance.

All I need now is clear skies. that will be next year then.