Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Considering an OAG for my 11" SCT

  • Please log in to reply
14 replies to this topic

#1 DSO_Viewer

DSO_Viewer

    Viking 1

  • -----
  • topic starter
  • Posts: 956
  • Joined: 03 Jan 2016

Posted 03 December 2019 - 06:28 PM

Hello all

 

I am strongly considering the ZWO OAG to use with my older Celestron 11 sct reduced to f/5 1400 mm focal length. I am currently using an 80 mm refractor piggybacked on my C11 and sometimes have issues with flexsure and mirror shift. I have an ASI290MM with a 6 mm diagonal sensor and my Orion SSAG with a 8.5 mm  diagonal sensor and was wondering if OAG will work as in being able to find a guide star in such a small FOV?

 

Steve



#2 f300v10

f300v10

    Ranger 4

  • -----
  • Posts: 348
  • Joined: 16 Sep 2018
  • Loc: Marietta, GA

Posted 03 December 2019 - 07:25 PM

Steve,

 

I use the Celestron OAG with a ASI290mini on my C11 reduced to f6.5.  To date I have had a viable guide Star in the frame each time without having to hunt for one.  I did find binning the 290mm 2x2 gave a better image scale for guiding.  
 

Scott


  • NuclearRoy likes this

#3 DSO_Viewer

DSO_Viewer

    Viking 1

  • -----
  • topic starter
  • Posts: 956
  • Joined: 03 Jan 2016

Posted 03 December 2019 - 07:50 PM

Steve,

 

I use the Celestron OAG with a ASI290mini on my C11 reduced to f6.5.  To date I have had a viable guide Star in the frame each time without having to hunt for one.  I did find binning the 290mm 2x2 gave a better image scale for guiding.  
 

Scott

This is good to know and binning helps. Thank you so much Scott.

 

Steve



#4 kisstek

kisstek

    Ranger 4

  • *****
  • Posts: 375
  • Joined: 25 Jul 2018

Posted 03 December 2019 - 08:07 PM

I also use a ASI290mm on the ZWO OAG but on my C6, no reducer, 1600mm fl. I've never had an issue finding a guide star. One suggestion if you go with the ZWO OAG, get the helical focuser for it. I found trying to slide the guide camera in and out to be a real pain.


  • DSO_Viewer likes this

#5 f300v10

f300v10

    Ranger 4

  • -----
  • Posts: 348
  • Joined: 16 Sep 2018
  • Loc: Marietta, GA

Posted 03 December 2019 - 10:35 PM

I also use a ASI290mm on the ZWO OAG but on my C6, no reducer, 1600mm fl. I've never had an issue finding a guide star. One suggestion if you go with the ZWO OAG, get the helical focuser for it. I found trying to slide the guide camera in and out to be a real pain.

Yes the helical focuser is a big plus.  Also whenever possible I get the guide camera para-focal with the imaging camera in the day time, at least until you learn the approximate correct position. 


  • DSO_Viewer likes this

#6 DSO_Viewer

DSO_Viewer

    Viking 1

  • -----
  • topic starter
  • Posts: 956
  • Joined: 03 Jan 2016

Posted 03 December 2019 - 10:52 PM

Yes the helical focuser is a big plus.  Also whenever possible I get the guide camera para-focal with the imaging camera in the day time, at least until you learn the approximate correct position. 

Great helpful information and thanks to you both.

 

Steve



#7 NuclearRoy

NuclearRoy

    Mariner 2

  • *****
  • Posts: 213
  • Joined: 11 Apr 2019
  • Loc: Pittsburgh, PA

Posted 04 December 2019 - 12:38 PM

Steve,

 

I use the Celestron OAG with a ASI290mini on my C11 reduced to f6.5.  To date I have had a viable guide Star in the frame each time without having to hunt for one.  I did find binning the 290mm 2x2 gave a better image scale for guiding.  
 

Scott

Same, but on an Edge HD8

Also 2x2 bin


  • DSO_Viewer likes this

#8 DSO_Viewer

DSO_Viewer

    Viking 1

  • -----
  • topic starter
  • Posts: 956
  • Joined: 03 Jan 2016

Posted 04 December 2019 - 12:49 PM

Sorry but one other question related to the OAG. I have a Meade 80 mm refractor piggybacked on top of my C11 and was wondering if I could also image with that scope at the same time as imaging with my C11 and guiding the mount through the OAG & C11? I am not sure if there will be drift due to the mirror not locked (older C11 with no locks). I know the image should be good with the C11 and OAG guiding it but not sure about the 80 mm scope sub-images.

 

Steve 



#9 f300v10

f300v10

    Ranger 4

  • -----
  • Posts: 348
  • Joined: 16 Sep 2018
  • Loc: Marietta, GA

Posted 04 December 2019 - 02:27 PM

Steve,

 

I've never tried to shoot piggybacked on my C11 + OAG, but I don't see why that wouldn't work as long as the 80mm is very firmly secured.  Mirror flop, if it did happen, should only impact a few subs when the mirror actually moves, it's not a continuous thing.  Also your guide image scale through the C11 will be much higher than the imaging scale on the 80mm, so I think you would be OK.


  • Stelios and DSO_Viewer like this

#10 DSO_Viewer

DSO_Viewer

    Viking 1

  • -----
  • topic starter
  • Posts: 956
  • Joined: 03 Jan 2016

Posted 04 December 2019 - 06:27 PM

Steve,

 

I've never tried to shoot piggybacked on my C11 + OAG, but I don't see why that wouldn't work as long as the 80mm is very firmly secured.  Mirror flop, if it did happen, should only impact a few subs when the mirror actually moves, it's not a continuous thing.  Also your guide image scale through the C11 will be much higher than the imaging scale on the 80mm, so I think you would be OK.

Sounds great Scott thank you so much for the help.

 

Steve



#11 Lead_Weight

Lead_Weight

    Apollo

  • *****
  • Posts: 1,004
  • Joined: 21 Jul 2016
  • Loc: Houston

Posted 05 December 2019 - 09:28 AM

I used the 290 with the ZWO OAG on an Edge 11. I did have a hard time finding guide stars, especially on galaxies that don't have a lot around them. I upgraded the 290 to the ZWO 174MM Mini, the larger pixels and FOV fixed all the issues, and I've not had any issues with guide stars since then.



#12 DSO_Viewer

DSO_Viewer

    Viking 1

  • -----
  • topic starter
  • Posts: 956
  • Joined: 03 Jan 2016

Posted 05 December 2019 - 01:14 PM

I used the 290 with the ZWO OAG on an Edge 11. I did have a hard time finding guide stars, especially on galaxies that don't have a lot around them. I upgraded the 290 to the ZWO 174MM Mini, the larger pixels and FOV fixed all the issues, and I've not had any issues with guide stars since then.

But isn't the 8.8 mm prism a little too small for the ZWO 174MM causing vignetting? Thank you.

 

Steve



#13 Lead_Weight

Lead_Weight

    Apollo

  • *****
  • Posts: 1,004
  • Joined: 21 Jul 2016
  • Loc: Houston

Posted 05 December 2019 - 07:20 PM

Yes, you will get some vignetting. You’ll see about 2/3 of the sensor. It’s not the sensor size that’s the issue though, it’s that the 174’s sensor is a lot more sensitive with much larger pixels. This can see stars that the 290 just can’t see. Alternatively, some Starlight Xpress guide cams have even larger pixels than the 174, and are even more suited to guiding. What I can tell you is that I tried both cameras, and no matter how I rotated the 290 guide camera, I just couldn’t pick out stars around M51, M101, or other galaxies that are in a sea of black. It wasn’t until I got the 174 that I could pick up some guide stars. I was able to use it on some objects, so your mileage may vary. But just speaking from my experience, the 174 always worked despite the vignetting.


  • Stelios and DSO_Viewer like this

#14 DSO_Viewer

DSO_Viewer

    Viking 1

  • -----
  • topic starter
  • Posts: 956
  • Joined: 03 Jan 2016

Posted 05 December 2019 - 09:47 PM

Yes, you will get some vignetting. You’ll see about 2/3 of the sensor. It’s not the sensor size that’s the issue though, it’s that the 174’s sensor is a lot more sensitive with much larger pixels. This can see stars that the 290 just can’t see. Alternatively, some Starlight Xpress guide cams have even larger pixels than the 174, and are even more suited to guiding. What I can tell you is that I tried both cameras, and no matter how I rotated the 290 guide camera, I just couldn’t pick out stars around M51, M101, or other galaxies that are in a sea of black. It wasn’t until I got the 174 that I could pick up some guide stars. I was able to use it on some objects, so your mileage may vary. But just speaking from my experience, the 174 always worked despite the vignetting.

I fully understand and appreciate your helpful suggested advice in which I will use. Thank you.

 

Steve



#15 Stelios

Stelios

    Cosmos

  • *****
  • Moderators
  • Posts: 7,994
  • Joined: 04 Oct 2003
  • Loc: West Hills, CA

Posted 05 December 2019 - 10:09 PM

What's the backfocus with the reducer for your C11? 

 

If it would accommodate a Celestron OAG, that would be a perfect match for the ASI174mm-mini and would give you the full FOV as well as the sensitivity advantages.


  • Lead_Weight likes this


CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics