C9.25 Guiding Test

[RyanJones]

I decided to take the opportunity while the moon is around to bolt my guide setup on top of my 9.25 SCT and do some guiding tests. To aid the short focal length guider I also added a .63 focal reducer to bring the focal length of the SCT down to a more palatable 1500mm. Still a stretch for a 400mm guider but that was what the test set out to prove. So here is my result ;

Celestron C9.25 w/ 0.63 focal reducer
60 x 180sec subs + 10 darks
Canon 350d astromodified @ iso 800
STC Duo Filter
Sky-Watcher 80/400 guide scope w/ Nexguide SAG
HEQ5 pro
Bortle 8 skies w/ 98% moon

Image cropped for asthetics

[billdan]

The stars at the bottom of the image look very good, the stars at the top look a bit elliptical (which could be collimation or camera tilt).
The stars in the centre have halo's around them which points to some dew on the corrector plate.

The pillars of creation came out well and with a few more subs you could get more detail in them.

:thumbsup:

[xelasnave]

It looks as if the guiding is ok and I agree with Bill on his explanation of the other aspects. It will be interesting to how the new combo works in the future.
Well done.

alex

[The_bluester]

I have used my C925 a reasonable amount for AP, what I did find very beneficial was using an off axis guider. So far off the centre of the FOV the guide stars look terrible but it works.

I did find that any sort of focus activity and a large enough change in pointing showed up as mirror movement but I don't know if that would end up relating to having to toss out the occasional sub or having movement visible in lots of subs.

[RyanJones]

Thank you for your input guys.

The Halos are from over excited processing in the star reduction phase rather than dew or dust. I see the tilt though. This doesn’t surprise me as I sometimes have similar issues when using my Newt. I think to help this I’m going to reduce the weight of the camera by moving the remote intervelometer from the hot shoe to my distribution box and just run another cable to the camera.

Re: OAG, I’ve been reluctant to go down this path because honestly I don’t know how well the Nexguide will handle it. It’s pretty fussy with the brightness of stars and is really quite sensitive to focus. Given that it only gives me a digital representation of stars rather than an image, I think it might be quite hard to get right. I agree though that OAG is the ideal way to go for such long focal lengths.

[LostInSp_ce]

Ryan I had a similar problem to yours show up in my images when I was testing things earlier on in the year and found it to be tilt from the rotator which hadn't been tightened fully. So maybe do a close inspection of all your contact points to see if anything has come loose or is flexing under load.

[RyanJones]

Thank you for the suggestion. When you say “ rotator “ what part is that exactly ? I will check that all mounting parts are tight though. Cheers

[LostInSp_ce]

My problem with the rotator was on a refractor but you may not have one on your Newt. Even so your setup is not immune from possible tilt. Check all connections around your imaging train e.g focuser, camera, spacers, filters anything that connects via threads, compression rings e.t.c. Also keep an eye out for any cable tugs that could be happening to your camera as the mount slews around from one position to another.

[RyanJones]

I’ll check all of my fittings next time I’m out and see if I can find any areas of flex. Reducing the weight of the camera can’t hurt though for both setups as if there is any room for movement, the less weight, the less likely it is to occur. Thank you again for you advice :)