120mm f/8.3 guidescope?

[Kaptain Klevtsov]

Any body got any good ideas how I might use my long Frac. as a guide scope for guiding the Mak?

I'm thinking a double barreled approach would be good, with the mak. fixed and the Frac. in some kind of adjustable system to allow a good guide star to be picked up. A big set of guide rings would be possible, but I'm worried about the frac. slipping.

One method that has come to mind is to fit the frac. rings at 90 degrees to each other and fit long studs to the rings. The custom made mount would have fittings to take the studs and have a nut each side of the fixed bit to allow adjustment. The front ring would be adjustable up/down, the rear ring would do right/left.

Using a Toucam I've guided using an f/8 camera lens, so I should be able to get a guide star to work with this setup, but maybe not manage to barlow the thing so that the guiding and imaging are the same in arc seconds per pixel.

I think the over and under method would be a bit heavy and require more counterweights than I have at present (especially as some plonker nicked my big lumps of cast iron out of the yard before I could drill all the holes in them).

Captain Chaos

[GordonCopestake]

I would mount side by side and use a FR on the frac. There is likely to be a star in the frac FOV then whilst the mak images. For £50 though you can have a 70mm Vixen guide scope from ebay thats light as a feather......

[Kaptain Klevtsov]

Or just use the ST80?

Gordon, the whole point is to go long with the guide 'scope to increase the guiding accuracy so that I can have a proper go with the Mak. on DSOs. Planetary Nebs. look pretty awesome in the images that I've seen so if I can get to grips with guiding with good accuracy, the long subs required at f/14 could be manageable.

Plan A was to use the ST80, maybe with a Barlow to give 800mm focal length at f/10 - not too far away from the big Frac., but not quite as good, but still more aperture than the Vixen 70mm, so more stars to guide by. I'm guessing that finding one would be easier as I can use a plain EP in the diagonal to get a wide FOV, centre the best star, then add Barlow and webcam.

If I thought that I could get by with binning 2X, I may as well use the SC3 on the Newt. as that will give the same image scale, similar exposure requirements etc. to using the HR16 on the Mak.

I want to find out what this OMC140 thing can do imageing wise, because visually it's pin-point and coma free. Because it doesn't get dark here I can't see the fainter fuzzies with it, so I thought that it would be fun to image with it.

The initial plan is to get a super-accurate guiding system organised, just to see if I can, and only then find out that the seeing stops it from working.

Guiding through the Newt. works down to +/- 1 pixel on the guidescope, so I think it's possible, but the Newt. is too big to plonk next to the Mak. (I think).

It's all just bits of the Kamera Sutra that I'd like to try for now though, due to the clouds.

Captain Chaos

[MartinB]

Think the side by side plan is a good one CC. Can't remember what guide software you are using. Maxim guides at sub pixel accuracy and the advice I have received from some very expert people is that I should have no problem guiding my 900mm ED120 with a 400mm ZS66. I would have thought whatever software you are using would be able to do something similar.

[GordonCopestake]

I would stick with the ST80 in that case CC, the 120 will pick up more stars and have more magnification but the faster ST80 would work better I would have thought. Although i'm the first to admit i'm no expert!

[Vega]

:shock: Would sure love to see a pic of this when you set her up.