OAG Problems

[carlstronomy]

Hi all hoping someone can help. I have just acquired a Celestron OAG for my SCT9.25. I was struggling getting a star so I went to Jupiter. After some moving and messing around I got in the the CCD chip, but when I looked at my image train Jupiter was now way out of the centre of the cross hairs and will not be visible at the main camera? I can reach focus all is good in that respect, but when I put the star or Jupiter in the cross hair I can rotate my OAG 360 degrees and it will not show.
I was under the impression that an OAG was the best way to go as there was not flexure etc. but it seems a little silly if the image trains don't line up.
There are no moving parts to misalign the two image trains so I am a little confused:question:

:shrug:

Thanks
Carl

[codemonkey]

Hey Carl,

That's by design; an OAG works by picking up light from outside the field of view of your main camera. If it didn't do this, you'd see the OAG mirror obscuring part of the image from your main camera which wouldn't make people too happy :-)

Cheers,
Lee

[Amaranthus]

For planetary imaging, you shouldn't need guiding. You can typically only take shots for a few minutes at a time (after that, planetary rotation becomes a problem for stacking). Within that time, with decent polar alignment, the planet should stay on the sensor. Your video stacking program will have no issue in dealing with the frame-by-frame drift.

[carlstronomy]

So what you are trying to tell me if you cant find a star in your 360 degree motion when you have your image in your main camera view then an OAG is useless? :lol:

In that case my short tube 80 is much better as my guide scope for my F 10 scope.

So does anyone want to buy a brand new OAG? It would probably be use full to some with a wide field of view :P

Carl

[carlstronomy]

Barry, I am not taking planetary with a OAG that certainly would be a waste of time! I used Jupiter to see if I could see anything through the OAG as it nice and bright and has moons, non of which could be picked up with OAG.

Carl

[Chris85]

Have you considered trying a more sensitive guide cam?

[codemonkey]

That's the downside of an OAG, you have a fairly limited FOV. As Chris suggests, a sensitive guide camera is key. Making longer exposures with your guide camera might help too.

Have to say I'm somewhat excited about using a guidescope soon; only ever done OAG and I'm looking forward to getting rid of it... although my tune may swiftly change after using a guidescope!

[Nico13]

I'm guessing it's not planetary you want to do but just used Jupiter as a nice bright object to line up on.

I also recently went to OAG and at the same time from an SLR to a cooled camera and filter wheel. A big change a new learning curve.
I also was surprised how far off OAG was from what you are seeing with the main camera.
I had in the past with the SLR just used live view to align the targets wanted. Fortunately I have a side by side setup with the main imaging scope an RC8 and the secondary wide field an ED80 so that became my alignment scope with the SLR as both scopes have been very carefully aligned and point at the same piece of sky.
Problem solved for me.
Question what guide camera are you using, is it sensitive enough as the OAG setups need to be a bit more able to see the really faint stars because the guider field is usually pretty small and you don't get to choose.
As for being the best way to, yes 100% better than anything I'd used before so stick with it and let's know how you go.
I hope this has just let you know a bit more what to expect.

[Amaranthus]

Sorry Lee, guidescopes sucks :P I started with that, and eventually gave up in flexure-induced frustration, even at relatively short FL (it's more subtle, but still there...) I love my TOAG!

I agree that a sensitive cam is critical - I use the ASI120MM, and always get a lot of options, even in the most empty part of the sky.

[codemonkey]

lol don't tell me that Barry! *sticks fingers in ears*

I understood them to be fine on short focal length, and since I've given up on long focal lengths and have "downgraded" to a 900 and a 478 I figured that should be well within the range. I've already sold my OAG too :p

[Amaranthus]

I knew you'd done that Lee, I was cringing as I saw the events unfold, hah! I still see slight flex and poorer guiding generally, even at 384mm FL. But you're committed now, so see how you go. Lock your guidescope down REALLY tight - no 3-point delrin scope rings and suchlike!

[carlstronomy]

Thanks all for your input I am using a DBK21 as my guide camera. But as the manual states I have even tried a 32mm eye piece instead of a camera, put the scope dead in the milky way lots of stars there!! and I saw nothing through the reticle, I moved the telescope focus from stop to stop. I also tried the DBK21 at 5 second shots and still nothing.
Something just seems not right:question:

Lee, guide scopes are not as bad as you would think I am using a ST80 and a DBK21 and can get 4 minutes shots on an old 9.25 Ultima with wedge and a 6.3 reducer see image link below. I have purchased a NEQ6 but have not tried AP on it yet!!

http://astrob.in/91581/0/

Carl

[Amaranthus]

So, to confirm (based on your top post), it is focused. But at the same time as your main sensor? You must get the distance exactly right. You can get this approximately so in daylight, then refine at night.

[carlstronomy]

Barry, at this time I an not even looking at my main camera I am pretending it is not there. No mater how far in or out I focus I can getting nothing visible through the guide camera it as if it is not picking up enough light.
Yes the flat edge of the prism is towards to telescope and I have adjusted the prism all the way up and down (down collects more light and still nothing).

This one seems to have me stumped :confused2:

Carl

[carlstronomy]

In general would a either of the Orion Starshoot guide camera's give me a better result than my DBK21 and GPUSB for either my ST80 or OAG set ups?

Or is there any other guide camera's out there at a better price?

Carl

[Amaranthus]

What is your main cam? You could try attaching that to the OAG and see if you can pick up stars then (i.e. to confirm whether it is a sensitivity problem). I tried autoguiding for a while with a Celestron NI5 colour cam, and it was frustratingly insensitive even through an 120mm frac! It would have been useless with an OAG. So perhaps this is your problem.