Off axis guiding on a sct

[h0ughy]

What do you think of this item?

https://www.celestron.com/products/off-axis-guider

Will it do the job or a zwo version or the Orion one?

[Sunfish]

I use one on an SCT , and also on the fs102 and a 200 newt.

Comes with many adapters , double dovetails and is very rigid with a large aperture available and a large adjustable pick off prism .

[h0ughy]

Do you also use a crayford focuser on the sct?

[The_bluester]

I am using a QHY medium OAG on a Celestron C925 with a ZWO 290MM mini guide camera. I went to the QHY from an Orion Thin OAG as I found the Orion not to be rigid enough for the job. The QHY is only about 13mm thick so it works on the SCT with the 0.63 reducer backfocus requirements, and the threaded adapter plates both sides are fixed with screws front to back so it is nice and rigid, on my ASI2600 I would be able to use the screws to fit it directly to the tilt plate on the front of the camera if I wanted to use it on that cam.

[Sunfish]

No . I only use main focus with a dc focuser.
So I have plenty of backfocus available.

The Celestron is not as bulky as it looks and you can thread into the dovetail plates but certainly takes up a lot more space than the thin types.

[h0ughy]

so do you use the main scope focuser or a crayford type?

[h0ughy]

thanks

[strongmanmike]

The Lumicon Giant Easy Guider/reducer was the gold standard back in the day, if you can get hold of one :thumbsup:

Mike

[h0ughy]

i sold yours years ago mike;)

[strongmanmike]

Aaaah yeeeah...I remember :) why'd you do that, ya duffa? You can still get them.

Mike

[The_bluester]

I use the standard C925 focus mechanism with a focus motor to drive it.

[h0ughy]

Thanks for the feedback

[The_bluester]

I am thinking of designing and getting a custom adapter made to move the M42 rotator that is between the guider and main camera to in front of the guider. Rotating the assembly is a bit of a kludge job at present, you have to loosen the SCT thread ring between the reducer and guider. The rotator is there as it suited the spacing.

[h0ughy]

I see what you mean

[The_bluester]

It is doable but a bit of a pain working around the focus motor and with the thread ring so close to the OAG.

Better do some measurements and work out what I need spacer/adapter wise to make it work. Using plate solving to set the angle is easy but it would be even easier if actually moving the camera was a single thumbscrew job. The rotator seems good quality and does not seem to introduce tilt when you move it, which is more than I can say for some other gear I have had.

[h0ughy]

Well I ordered a bintel sct crayford focuser and I have a spare EAF focus motor that I was going to put on my lunt 60, and I ordered the celestron OAG. It just looked more robust?

I am hoping that the bintel focuser will do the trick. The celestron OAG can be rotated according to the blurb.So it will either work or not? Surely how hard can it be......

[The_bluester]

EAF as in the ZWO motor? Which SCT are you using? I did see that ZWO have designed a bracket and coupling to put the EAF on the C8, 925, 11 and 14. I was thinking of buying another EAF (I use one on my other scope) and fitting it to the C925 as the Celestron motor lacks a temperature sensor.

[h0ughy]

I bought myself a little lovely 12 Meade lx200r, yet to get it, it's north of me

It's the full kit eaf

[assbutt94]

The celestron OAG seems pretty solid and a good option.

One downside to it is you may not be able to get the guide camera to the correct back focus depending on the setup. This was my experience.

For reference, I am using an edge8, 0.7x reducer, Celestron OAG, Filter wheel and 1600mm camera in that order, with the 1600mm sensor at about 105mm backfocus.

A 174mm could not reach optimum back focus in my case, as when screwing it onto the top of the helical focuser the cameras sensor is another 5mm above the top of the helical focuser. The 174mm MINI inserts into the helical focuser and so the sensor is way below the top of the focuser and I should easily get backfocus (yet to set it up).

Celestron have OAG documentation showing the back focus each item and adapter uses in the kit.
It would be nice if they gave information on the possible back focus measurements of the helical focuser so that I could have checked ahead of time.

My pick off prism also had a chip, I had to return the whole OAG, I couldn't just get a new prism thing sent on it's own to replace myself.

[h0ughy]

I do have a lodestar that I could use if it had to go in, so I take it you had to get it in closer? As I am inherently lazy I don't do mono, one shot colour pony for me so won't need filter wheel. That's why I thought the celestron oag would be OK I am hoping the crayford focuser will work out for me.

Don't suppose you have a shot of your image train?

[assbutt94]

If you require a longer back focus you will have more flexibility to achieve the distance required, and saving the 20mm required for a filter wheel is also very helpful. Had i not been using the reducer I could use a normal 174mm.
Heres an image of the image train

[h0ughy]

Thanks