Off Axis Guider woes

[pyrasanth]

Hi everybody,

I bought the Celestron off axis guider kit. I sent the email below to FLO to see if they can help with the issue of getting the guide camera to focus. I know the forum is very knowledgeable so I thought I would give you guys & girls a crack at the issue as well. Please remember that I'm working a bit blind on this issue (excuse the pun) as I know very little about OAG in general. Please consider my last question if the lodestar auto guider would be a better option & eliminate the issue.

"Hi,

I bought a Celestron OAG from you last week.

This is being used on the C11 Edge with the 0.7 focal reducer which has a back focus of 146mm. The CCD is the Atik 490EX again supplied by yourselves. The Atik 490EX has a back focus of 13mm. I can bring the camera to focus easily using the telescope focuser.

Now for the problem part. I have a Celestron Skyris 618C which I'm trying to use as the guide camera. This has a back focus of 19 mm using the supplied nose adapter or 17.5 mm without. I used the suggested spacer settings in the PDF shown for the Nightscape camera & the Edge series telescopes from 9.25" and above. The problem seems to be focusing on a few close trees is that using the Skyris there does not seem to be enough "In" focus. The helical focuser will rack outwards but of course not inwards. I wonder if you know of a solution to this with the supplied adapters or is the Skyris simply incompatible because of the large difference in back focus between the 2 devices. I know that the prism can be moved but I don't want to play with this if there is an easier solution.

If you don't know the answer to the question would it be possible for you to contact anybody you know at Celestron to see if it is possible to use this combination of CCD cameras.

Am I right in thinking that If I bought the Lodestar Auto-guider from you I would not be affected with this issue as both the back focus in the Atik & the Lodestar are both 13mm thus would be almost par-focal? However this solution would cost money so its always preferable to try & use what I have."

[lensman57]

Hi everybody,

I bought the Celestron off axis guider kit. I sent the email below to FLO to see if they can help with the issue of getting the guide camera to focus. I know the forum is very knowledgeable so I thought I would give you guys & girls a crack at the issue as well. Please remember that I'm working a bit blind on this issue (excuse the pun) as I know very little about OAG in general. Please consider my last question if the lodestar auto guider would be a better option & eliminate the issue.

"Hi,

I bought a Celestron OAG from you last week.

This is being used on the C11 Edge with the 0.7 focal reducer which has a back focus of 146mm. The CCD is the Atik 490EX again supplied by yourselves. The Atik 490EX has a back focus of 13mm. I can bring the camera to focus easily using the telescope focuser.

Now for the problem part. I have a Celestron Skyris 618C which I'm trying to use as the guide camera. This has a back focus of 19 mm using the supplied nose adapter or 17.5 mm without. I used the suggested spacer settings in the PDF shown for the Nightscape camera & the Edge series telescopes from 9.25" and above. The problem seems to be focusing on a few close trees is that using the Skyris there does not seem to be enough "In" focus. The helical focuser will rack outwards but of course not inwards. I wonder if you know of a solution to this with the supplied adapters or is the Skyris simply incompatible because of the large difference in back focus between the 2 devices. I know that the prism can be moved but I don't want to play with this if there is an easier solution.

If you don't know the answer to the question would it be possible for you to contact anybody you know at Celestron to see if it is possible to use this combination of CCD cameras.

Am I right in thinking that If I bought the Lodestar Auto-guider from you I would not be affected with this issue as both the back focus in the Atik & the Lodestar are both 13mm thus would be almost par-focal? However this solution would cost money so its always preferable to try & use what I have."

You need to try and focus at or near true infinity not close trees. With a long FL of the SCT your problem is actually worse than a wide APO so try and get on a bright star such a vega first.

A.G

[D4N]

I worked out which spacers to use with mine by focusing in the day on trees 12km away, then it's just a case of fine tuning at night but that in itself can be tricky enough when your not even sure that there is something there to focus on.

TSED70Q, iOptron Smart EQ pro, ASI-120MM, Finepix S5 pro.

[pyrasanth]

Thanks for your help Guys!

I worked it out in the end with your help. I carefully read the OAG PDF guide as there was no manual in the box. It said that if you cant get the guide ccd to focus inwards (my problem) you need to add additional spacers between the OAG & the camera. I found a "nest" of spacers of various sizes screwed together in the box & added a very large & a small spacer. This worked! I can now focus the imaging CCD on some trees and focus the guider to get an offset of the same group of trees where previously I got nothing from the guider- so result!

I just need to now fine tune the guider on some real stars. I will pick a heavy star cluster so at least I will find a star or two to focus the guider. I'm really looking forward to capturing some deep sky objects.

The telescope is polar aligned with a plate solve. A pointing model is in place & the guider is now nearly setup. I will be good to go.

[Pickwick]

Hi Guys,

I use a loadstar with Maxim DL. If you set the exposure in the continuous mode this aids focusing. Usually there is suffiient back focus to get this right ie get the stars as pin point as posible but this is not critical. Should the back focus be insuffucient you can get a add on that will screw into the loadstar then cut it to length. By the way if you are going for the Loastar get the latest version  X2 because it has a proper autoguider socket.

I am not versed in the set up you have why not give Micheal Haty a bell for advise.