Getting a TS OAG working

[rsamuel]

Hi all,

I'm using an MN190 for my main imaging scope with an Atik 314L+ and EFW2 for taking the pictures, and have been using a Lodestar on an ED80 mounted side-by-side on an EQ6 for guiding. I've never really got it balanced quite right, and so recently bought a TS off-axis guider so that I could do away with the two scope setup. However, I've not been able to get the OAG working right. I'm sure it's just because I've never managed to find the right focus position for it, but I'd be interested to hear how other people with a similar setup have their systems configured - are additional spacers needed on either the imaging camera or the guide camera, for example?

Thanks!

Bob

[Tim]

Welcome to the forum Bob!

I have used a similar setup on an MN190 to good effect.

Send me some pics of what you have, or if you are near to Coventry pop over and i'll give you a hand. Best to do that by private message though, I have a terrible memory and will likely forget to come back to this thread :s

You will get MUCH better results with the OAG, you'll be able to take single exposures hours long for instance with no signs of flex etc.

All the pics in my album here were pretty much taken with the same setup as you have.

Stargazers Lounge - Tim's Album: Mak-Newt 190 Pictures

So, just give me a shout if I can help

Tim

[BlueAstra]

I use a SX Lodestar on my SX OAG. It was a nightmare trying to setup during a night session. I found it was much easier to set it up during the day, both to get the best position for the prism to reduce shading (vignetting), and to get approximately the best focus for the OAG camera after focusing the main imaging camera. During the night session I then only had to tweak the OAG camera focus after focussing the main camera. This thread here may be of interest for you.

[rsamuel]

Thanks, Tim - you've got some nice pictures there!! I'm just outside Cambridge, so it's a bit far to pop over for a look, but I might do if I don't get it sorted! I'll drop you a PM, though it may take me a couple of days to get round to it.

BlueAstra - thanks for the link. I dream of getting OAG images like that! I tried setting up on the moon during the day yesterday, but couldn't get anything other than an fuzzy, over-exposed mess. I was also seeing what seemed to be just a rectangular area in the Lodestar image that would correspond to the shape of the prism, rather than a nice circular, albeit somewhat vignetted, image.

Cheers,

Bob

[BlueAstra]

I had to use a very short exposure time to get an image, any direct sunshine would kill it. I got the best results on a cloudy day with a fast exposure. It sounds like a focus issue, try moving it while watching the image, even 'hovering' it above the OAG. The focus may be further away then you think. The important thing is to focus the main camera first then not touch the focusser. Then try moving the guide cam around. Once you have guide cam focus you can then move the prism in and out to reduce any shading on the main camera.

[Catanonia]

They are a pain and had the same trouble with a QHY9 and TSOAG.

As said, get the main camera focused with a bahnitov mask and lock it rigid.

Now have some T2 extenders ready.

1. Put the prism so it is paralell to the top of the main image chip.

2. Don't put it in too far, judge by eye that it will not obscure the main chip.

3. At night, find a rich star field, Deneb area works well.

4. Slowly adjust the guide cam end until you can see something on PHD. Use at least 2 seconds on PHD refresh. Start from one extreme of the prism arm to the other in small increments. Remember to take PHD darks.

5. Don't tighten too much, the TS OAG has a habit of denting the grooves.

6. You may need to add a 5mm T2 thread to the guider end.

Put put simply, focus main cam, set the prism and don't move it. Only move the guide end.

If you fail with the above, move to another part of the sky and try again.

Once you have it, lock it all, measure and note it down, you should never need to change it again for the camera / TSOAG combination.

I tried during daylight, it was impossible for me with a CCD and QHY5

Afterwards, solder tipped grubs screws area good replacement for the dent causing screws they supply with the TS OAG. (PsychoBilly to thank for that tip)

[rsamuel]

Thanks again, folks. It sounds as though I've been trying to do the right thing, but just haven't got it sussed yet. I was beginning to wonder if the guidecam needed to be moved closer to the scope once the imaging camera was focussed - that would be somewhat difficult! I have some C-thread spacers for the Lodestar and tried putting those into the system the other night, but couldn't pick up anything at all using (dark-corrected) PhD.

More practice needed, methinks!

[rsamuel]

Success!!

Well, I had another go last night, and got it working! It's quite tricky making the adjustment of the focus on the guide camera once the main image focus is right, but I got there in the end. Interesting that the out-of-focus images throught the OAG were semi-circular arcs - has anyone else seen that?

The thing that did disappoint me was that the guide stars were really quite faint. I had a quick go at the Flame nebula, and the only guide star I could make out was presumably Alnitak; that doesn't bode well for trying to capture objects that have no bright stars near them. The attached images show the PhD view that I had, and also the very quick image of the Flame just to prove I got something!

Thanks again to everybody for your help.

Bob

[Tim]

Great, you did it!!

That doesnt look like Alnitak in the PHD image, besides, you wont be able to get the guide star in the image anyway, and its there in the Flame pic.

You do have three positions for the camera with the TS OAG, but I always found plenty of guide stars were available no matter what the target at f5.3 with the MN190, so you'll probably be ok.

No stopping you now

[Gina]

Nice image - well done I'd be well pleased with that.

[rsamuel]

Thanks Gina, but I know I can do better

[hayju01]

Good to see you got it fixed bob, I'll be looking to use my OAG with QHY very soon ( had it 6 months just never the time) so I know where to visit if I need a hand