THREE lousy hours! (off-axis autoguiding)

[Tim]

Its taken three hours in the freezing cold to do it, but i have finally managed to get my autoguiding going through my Off-axis guider.

So right now I am merrily taking 15 minute subs through my SCT @ F10, something which was impossible before. Yes I know the stars will be bloaty, yes I know I would be better at F6.3, but I reckon thats not possible to do, at least with the kit I have.

For the qhy8, the back focus had to be extended quite a bit to get the guide camera into focus as well. I have temporarily borrowed my Baader MPCC, removed the lenses, and used the tube for extra length, as that screwed on to my 2" push fit to M42 adapter. On the DSI, I took the filter glass out of some cheap filters, and used the casings to get the right focus on the guide camera. It is that part which is very hard. I used the moon to get close, but when you get onto target, you need to refocus for a guide star, and even then its a bit fuzzy at F10. Its a good job PHD doesnt mind slightly fuzzy

So I am awaiting these results with interest, as previously any pic through the SCT with an exposure length of greater than 180 secs had trailing stars due to differential flexure.

If only there was a more simple solution to OAG across the varieties of OTA's.

Cheers

TJ

[Merlin66]

Which off-axis guider are you using? Celestron? Meade? Lumicon?

Just interested, as I regularly use the Meade or the Lumicon on the 12" LX200 to guide my spectroscopes.........

[iancandler]

There is, but it involves throwing a lot of cash at a QSI camera, the 540 model can be supplied with a built in OAG that adds virtually nothing to the chain, so meaning the camera body can be that much closer to the scope.

http://www.iankingimaging.com/show_products.php?category=113

*scroll down to QSI 500 Series Cameras With Off Axis Guider*

[RobH]

I'll be interested to see how you get on with the OAG Tim, looking forward to reports.

Getting rid of a separate guidescope would be a real bonus!

Cheers

Rob

[Tim]

do you get any flex with your 14" Rob?

[RobH]

I've had dreadful problems which still aren't completely resolved when using the 14 as the guide for the 80mm WO Tim.

When I use the 100mm TAL as the guidescope for the 14 though, I have no issues and can go for 10 minutes at F10.

The problem with the WO is the long unsupported section with a camera and a motorised FW hanging on the end of it.

I've attached another tube ring which now supports this and has made it a lot better but it's still not right, and has caused problems of its own.

Cheers

Rob

[Merlin66]

Tj,

You still haven't mentioned which OAG body you are using??

[Tim]

I have the celestron OAG. It has an SCT thread at one end, is 55mm long, and has an m42 thread at the other end I think.

I took just over an hour of images of M81, with exposures ranging from 5 mins to 15mins, all at f10. The pics were the best I have had out of the SCT at F10, its just a shame there was such a bright moon and only moderate seeing, as there is a fair bit of noise in the image. Of course, at f10 the stars get bloaty, and it takes an age and a half to get an image, so I am really keen to get it down to f6.3. I have contacted a supplier of a different OAG that just might do the job.

It is only because I now have a DSI pro that I can consider autoguiding through the OAG. There are very few stars that find their way to the prism, but luckily the dsi can see even the very faint ones.

Cheers

TJ

[Tim]

Here is 4 x 15 mins.

Round stars! yay!

(click to enlarge)

[MartinB]

Well done TJ. If you are using off axis guiding you might as well go the whole hog and get an SX active optics unit.

The Sky 6 has great fov indicators, you can set up your main chip and your offset guider which is a great help for finding decent guide stars

[Tim]

Got a link Martin?

I have just managed to get both QHY8 and Meade DSI focussed together, using the F6.3 reducer. The qhy8 is at (what I have heard) is the recommended distance from the reducer, i.e. 110mm, and the DSI needed a little modification to bring it close enough to the prism to get it to focus.

Basically, I unscrewed the housing of the filter holder, which left a flat surface. Onto this I taped (just to test the theory) the 1.25" nosepiece that usually screws into the filter holder. This enabled the chip to be around 12mm closer to the prism. Using the moon, I first brought the qhy8 into focus, and then played with the setting on the dsi until that focussed too.

The theory proven, I have glued a 1.25" tube from an old eyepiece onto the DSI, which will allow me another 3mm closer to the prism as well if needs be.

Just need a clear moonless night now to test it on actual DSO pics, it's a real hunter's moon out there! Hopefully this setup will comprise my "close-up" kit, the GSO will give a fast wider field, and the WO72 will either guide for the GSO (and vice versa), or else be fitted with a dslr and mounted on the bar to image alongside the SCT with OAG. That's the plan! I'm sure the practice will be different.

Cheers

TJ

[ChrisEdu]

Here is 4 x 15 mins.

Round stars! yay!

(click to enlarge)

Nice picture.

[MartinB]

http://www.starlight-xpress.co.uk/SXV-AO.htm

[Tim]

Thanks Martin.

Have you found it makes a difference? And can any imaging camera go on the back of it? Does the guidecam have to be an SX unit?

[MartinB]

It is a bit of a beast Tim and it does add a fair bit to the optical path. You can certainly use none SX cameras including QHY8. Guide cameras is a bit trickier. The SX guide cams screw onto the off axis bit. Not sure whether you could connect up other cameras such as a QHY5, I'll have a look. The greater the sensitivity and the lower the noise of the guidecam the better. A decent field of view is also handy. They were the reasons for me getting a Lodestar.

It does make a difference and allows you to work at beyond the normal seeing limits especially with a decent guide star. The M1 (F10 F/L 2500) I've just posted was using guide star exposures of 1/10th second and the guiding was going through about 6-7 cycles per second.

Obviously it's a fair old expense and it adds an extra raft of complication. Once you get the hang of it it's awesome.