I would like to return my SG-2/Aluma filter wheel to the factory for troubleshooting

No. One was from the SC2 the other is from the 694. The two look very different.

 

This is my latest effort with my SC2. I am concerned that my telescope system, a Celestron CM-1100 working at f/6.3 is not providing a large enough image area to fully illuminate the Aluma 694 CCD and the SC2 guiding chip. Here is an image I took recently. You can see a star and I'm sure it's a star. But when I try to move the star to the center of the SC2 fov, it eventually fades and disappears. The lower and to the right, the more circular and brighter the star gets.

 

Yes, everything is 2-inch. Here are a few images of the camera/filter wheel/SC2/adapter/focuser/telescope

 

Yes, everything is 2-inch. Here are a few images of the camera/filter wheel/SC2/adapter/focuser/telescope

 

One more image...

 

You said your telescope is a Celestron CM1100 at f/6.3, I'm pretty familiar with most telescopes and I don't know what this is and it doesn't pull up this specific model with an internet search. Can you post a picture of the whole OTA so we can see exactly what you have?

I agree with Colin, if you are using a reducer, take it out of the optical train for now, the reducer decreases the size of the image circle and will make it more difficult for the OAG to see stars. I would also move the pick off mirror all the way in for now, it will likely affect the main imaging camera but we dont' care for now, this will also help in getting more stars on your OAG camera.

Getting stars on your OAG and focused isn't simple, but it also shouldn't be this difficult, there is something going on that isn't right here.

 

To answer a few questions, and by the way. Thank you for all of the suggestions and support! It is very much appreciated. First, there is a Celestron f/6.3 focal length reducer in the light path. You cannot see it in the image I posted, but it is in the focuser housing. Second, right now the SC2 pick-off prism is now all the way into the light path and from what I can see, there is no protective coating on the pick-off prism. I will remove the focal length reducer and experiment with that configuration as soon as it stops raining! :-(
Again, thanks to all for the help.
John G.

 

Here are some results of my tests and investigations...First of all, there was a piece of clear protective tape covering the pick-off prism! That was a biggie. After I removed it I reassembled the system and tried again. No difference. I ran through the entire range of focus and still no stars or bright patches. So, I then removed the f/6.3 focal length reducer and that did the trick after I re-focused the telescope again. I was able to get roundish stars on the SC2 fov. It was tough though to slew to a field and actually get a star to guide on. But, now working at f/10 is a lot tougher. It's a smaller fov and there are far fewer stars in the main camera fov. In fact there weren't enough stars in most cases to do a closed loop slew. This will be an issue that I will work on. So, now that we know the SC2 works at f/10, I would like to go back to f/6.3 since this plate scale at f/6.3 is much better with my small pixels.

So, thanks for all the assistance and patience everyone! When I tried to autoguide using the SC2, it did not hold the star in the guiding box. When I initiated the autoguide command, the guide star just drifted out of the fov rather quickly. Again, I'm using the TheSkyX Pro camera add-on and this has worked very well for me with my old ST9XE. But for some reason, it seemed like the autoguider was not sending commands to the mount or the mount was not receiving them. Or, maybe it was because it was 3:30 AM! Anyway, one thing at a time. I suspect I need to upgrade my ASCOM or the SC2 driver as Colin suggested in an earlier post. I will be working on this the next time I go out. I made good progress, however. Thank you all again!

 

Good to hear you are making progress and the tape on the prism sure wasn't helping anything.

Now that you can get stars on the guide camera I would suggest pointing the scope at an open cluster, get it roughly centered on the guide chip, do say a 20 second exposure and plate solve the guide image. Then you can figure out the offset of the guide image from your main image. I've never used the sky, I use MaixmDL for centering of my targets and I have an offset box that shows exactly where the guide chip is in relation to the main chip, it makes getting a bright enough guide star on the guide chip MUCH easier. I don't know if the Sky has something similar but I would imagine that it does.

BTW I'm using an 8" Edge OTA at F10 with the STT-8300 and the filter wheel with the built in OAG so I have a similar setup.

Can you please post a picture of the front of your OTA with the cap off so we can see exactly what you have?

 

OK so an 11" SCT on a non-goto mount, that is certainly going to be a challenge.....

 

Hello Joshua:
The manual that Colin showed is the manual for the CM-1100 and the Los Mandy mount that was sold together back then. I just bought the CM-1100 OTA. It is on a Paramount MX mount.
John G.

 

Ah ok, that is a much better mount then. So it is a standard C-11 OTA. I would have thought even with the reducer you should still have a large enough image circle for the OAG.

What reducer are you using and what components are you using to connect everything? Maybe something is causing some vignetting? How about your spacing from the back of the reducer to the camera?

 

I used to use this same telescope and mount configuration with an SBIG ST9XE. It has an on board guiding sensor. It was perfect for my system. However last spring it failed after 20 years of service. The new cameras all have small pixels and large sensors.

Immediately coming out of the telescope, I have a Moonlight motorized focuser. The Celestron f/6.3 focal length reducer placed inside the focuser, the the Aluma FW8/SC2 is next. The length of the focuser housing is roughly 4 - 5 inches. I use this set up for observing exoplanet transits and nothing else. I am working on my Ph.D. in this field and it is critical for me to get this working.

There isn't much space after the reducer as the FW/SC2/Aluma mate directly to it. Last night after I removed the reducer was the very first time I actually saw round stars on the guide chip. But, the ideal situation was to get those round stars on the guiding chip working at f/6.3 and not f/10. I also though the image circle would be large enough top illuminate the main sensor and the guide chip in the SC2. I was disappointed last night when I finally got a decent star in the guide sensor fov and it just wandered out of the guiding chip's fov.

 

Hi John.

A few ideas….

If you were happy and could work with the sensor size of the old ST9XE would you be able to accept a compromise when running with the reducer at f/6.3 and just allow the shadow of the pickup mirror/prism to intrude into the main camera image for exoplanet photometry?

Unlike general nightscape astrophotography it’s not so important how the frame “looks” just so long as the photometry data can be obtained.

Plate solve will still work even with the main sensor partially obscured, as it will solve on the stars it can find, you could even setup a permanent sub-frame size for the Aluma in TheSky camera settings, slightly smaller than full-field and a little closer to the old ST9XE size, that would allow you to bring the guider pickup even further into the image circle at f/6.3 and not shadow the (subframed) Aluma image at all.

Otherwise… would mounting a cheap achromatic refractor of ~6-700mm fl atop the C11 and a separate guide-cam give you a much bigger field to find a guide star while leaving the Aluma to run at f/6.3 full frame, unobscured?

Sure there will be some differential flex and the Aluma star images may show some ellipticity but that shouldn’t prevent useful photometry data still being obtained for exoplanet transits.

William.