Fools jump in...

[morls]

Ok, I've decided to get serious about my goal of photographing deep space objects with my 180 Mak. It might be overly ambitious, especially as I'm new to astrophotography, but whatever happens it'll be a fun trip.

My main imaging setup is a Skywatcher 180mm Mak (f/l 2700mm native) on an un-modded NEQ6, ASI290MM and a set of Baader LRGB filters. I'll add narrowband as this project develops. My priority now is to set up a guiding system, and so I was wondering at the outset whether to go with a guidescope setup or an OAG setup. If I was to go guidescope, I'm looking at the skywatcher Evoguide 50ED, Evostar 72ED or the Evolux 62ED. Ideally, I'd like to be able to use the guidescope for imaging in its own right.

Any advice would be greatly appreciated.

Stephen

[RyanJones]

A bit of a catch 22 in my humble opinion Stephen. At that focal length OAG is the only way to go. Having said that, setting up an OAG is a bit steeper learning curve with no previous guiding experience. For the record a focal length of 2700mm is going to be a challenge regardless but good on you for diving in. Another option is to buy an 0.3 reducer as well. It will open up your field of view to a considerable amount more DSOs, it will make your imaging system faster essentially receiving more light in less time and as an added bonus, at a focal length of 810 mm, you could easily guide it with a conventional guide scope setup. Once you have mastered that setup you can buy an OAG for tighter fields for galaxies etc and apply the experience you’ve gained. In the long run you’ll end up with effectively 2 different imaging options.

Cheers

Ryan

[morls]

Thanks Ryan. At this stage I don't want to use a reducer, although I might be pushed that way in time. If this focal length rules out a guide scope then at least I know where to start with this. There seem to be a few options with regards OAG, and I was thinking of the ASI120 mini for guiding. I notice this is in your signature. Are you happy with this camera for guiding?

[RyanJones]

The 120mm works great for guidescope guiding in my experience. I did buy a ZWO OAG a while ago to use with my C9.25. I used it once and could find guide stars but my HEQ5 pro mount didn’t seem to be able to keep up with that sort of resolution. Since then I have tuned my mount to within an inch of its life but I haven’t tried it again so I can’t honestly give you a fair evaluation of its use in an OAG.

[Sunfish]

I bought a used Celestron OAG as it came with all of the required adapters , double dovetails and parts and is very robust and adaptable with a large aperture which provides a lot of adjustment . I use it on an 8 inch SCT and a Tak refractor and an f5 newt . With an astro camera and filter wheel it works fine on all those and with a DSLR , on the SCT and Tak. I am a bit of a novice with guiding but it works fine if you can carefully set up focus in the daylight hours and be prepared to confirm focus on the night. PhD reports 0.6 to 1.0 error mostly, good enough for 5-10 minutes.

On the Tak and SCT the helical guide camera focuser is great and on the newt with less back focus the OAG Guide camera focuser is removed for a fixed focus and direct thread of 120mms guide camera to OAG.

I have not used anything else really and once I had eq mod running on the Heq5 it worked fine. Works even better with a belt drive. Angels, Ha.

[morls]

Sounds like a good setup Ray. I'm currently trying to get some spec's on prism size, as I think a larger prism is better suited for this focal length. I'm leaning towards the Orion "Thin Off Axis Guider", but the helical focuser on the Celestron sounds good. ZWO also have a standalone helical focuser, but whether that would be compatible with the Orion is still something I need to check out.
My setup is/will be: Baader focuser - OAG - ZWO EFW - ASI290MM. I need to do some measuring or find some specs for the distance from prism to 290MM sensor, then I can decide whether I need a helical focuser for the guide camera. I think budget will limit me to the ASI120MM-mini.

[morls]

The Celestron has a prism size of 12.5mm, compared to 8mm for the ZWO. Along with the helical focuser and range of adapters the Celestron looks to be a great kit, so I've placed an order.
Thanks for the input everyone :)

[Sunfish]

The other big issue is aperture size on the telescope side for access to stars for the prism without a shadow on the image and ability to rotate easily. The Celestron can accommodate a very large telescope side connection and clear an APSC sensor. The SCT connection can be purchased in several sizes , a 48 mm low profile female dovetail connection comes in the box and I have had a 72mm dovetail made from a large SCT dovetail.

I am sure there are many other quality OAG systems but many of the cheaper ones are small aperture, non focussing, are not double dovetail and do not come equipped with a box full of robust dovetails and adapters.