Off-axis guider

[RobertM]

I'm considering buying one of these, has anyone experience of using one they could share.

Many thanks
Robert

[Rocket Pooch]

Yip,

I'd recomment it for many reasons, mainly because the guiding is really good, no flexture issues, but also you only need 1 dew heater etc.  But they take a little getting used too.

[Mike]

But they take a little getting used too.

In what respect ?

[Rocket Pooch]

Getting the focus of the guide cam par focal with the imaging cam, or at least close enough for the software to calculate a centroid.

[RobertM]

Thanks, but which one? there are so many ... there's the Telescope Service 'wafer thin' jobbie all the way up to the Giant Easy Guider plus a whole lot in between.  What makes it more difficult is that there aren't many critical dimensions mentioned.

I'll do some more research but any recommendation would help narrow the field.

Cheers
Robert

[Mike]

so how do you focus it ?

[Rocket Pooch]

Hi,

I have the Telecope Services one, its thin and is useful, I think, because you can still image at F2.8 with it in place.

Mike, you focus it by sliding the guide came up and down on a focus pole, its really tricky bit when you have the hang of it its ok.

Its outside now guiding away!!!  the first time in ages I've been bothered to image.

Chris

[RobertM]

Thanks Chris... now it's measurement time ...

[RobertM]

Chris, any chance of posting some pictures of the OAG on your equipment? If you could include a ruler then I could take some measurements.

Thanks
Robert

[MarkS]

He posted one here:
http://forum.orpington-astronomy.org.uk/index.php?topic=5990

[Rocket Pooch]

Hi,

Could do, but not sure what thats going to do but I will.

Chris

[RobertM]

It'll show me how much clearance there is for the guide camera based on where your guider is.  I don't think there will be a problem but you never can tell though from that image on the other post the clearance looks ok.

Is it very strong and can you see any weaknesses in the design?

Robert

[Mike]

I'm very interested in this system myself as flexure is definitely an issue. This system would be perfect for the guys with the HEQ-5's also as it would greatly reduce weight.

[Rocket Pooch]

Ok, the thing is only 9mm thick the back is a T mount and the front is?  Can't remember I think its 48mm.

Its really fiddly and you can only place the second camera at 120 deg angles and therefore if your guiding s/w can deal with RA/DEC totation your stuffed, this is not an issue with Maxim and AA.

The focusing is quite nasty, but they all are.

But, its wide at the front, thin and very rigid.

Look at it here you will see what I mean by fiddly http://www.telescope-service.com/accessories/start/accessoriesstart.html#TSOAG9

Chris

[Mike]

BTW these are cheaper from Modern Astronomy - http://www.modernastronomy.com/accessories.html#accOAG