13 replies to this topic

[John_robertson1953]

I own a Celestron 8” HD SCT, alt/az with a wedge, use .7X reducer & Hyperstar. Imaging camera: ASI183MC, non-cooled. 

What autoguider and camera would you recommend, paired best with this setup?  $200-$500 range. 
I appreciate any advice given. 
Thank you. 

[Mark Lovik]

Askar FMA180 with a small mono camera.  Pushes the cost a bit - but you get an alternative wide field imager along with a lightweight stable guider.  Boring (when it just works without fiddling) is good.  This would allow you to double the fov from your RASA configuration.

 

I use my old 178mm camera with it for guiding.  There are less expensive options for a good mono guide camera - but this is the camera I already own.

Edited by Mark Lovik, 26 January 2023 - 03:32 PM.

[rkinnett]

Use an OAG when you use the SCT in the standard configuration at 0.7x. Any mono guide cam including the cheap ones (e.g. QHY5LII-M) will get the job done, but larger pixels and lower noise (e.g. asi174mm mini) are more pleasant to work with.  The 290 is a good compromise and seems to be most popular.  Get a 30-50mm guide scope for use with Hyperstar, and use that with the same guide cam.  If your SCT came with a finder scope you could probably use that.

[bobzeq25]

With my RASA 8  (designed to eliminate mirror shift) I use this,

 

Base, screws to RASA over full tube length.  Very solid.  (That's necessary)

 

https://www.celestro...ovetail-bar-cge

 

Guidescope, mounts to base using the two included rings.  Very solid.  (That's necessary)  I threw away the silly finder shoe, using that is asking for annoying, hard to diagnose problems.

 

https://www.amazon.c...B015VUPS2I?th=1

 

This would work well with a 120MM mini guide camera.  Cheap.  I use a 174 MM Mini, just because I have one, not because it's significantly better.

 

The above setup works perfectly.  At least perfectly enough.  <smile>

 

If you have mirror shift, you'll need an off axis guider.

Edited by bobzeq25, 26 January 2023 - 03:30 PM.

[John_robertson1953]

Askar FMA180 with a small mono camera.  Pushes the cost a bit - but you get an alternative wide field imager along with a lightweight stable guider.  Boring (when it just works without fiddling) is good.  This would allow you to double the fov from your RASA configuration.

 

I use my old 178mm camera with it for guiding.  There are less expensive options for a good mono guide camera - but this is the camera I already own.

Thanks for info. 

Would I be able to use the FMA180 for both hyperstar & .7X reducer?

Also, you’re suggesting using the guider as an imaging camera (double the FOV)?

[John_robertson1953]

Use an OAG when you use the SCT in the standard configuration at 0.7x. Any mono guide cam including the cheap ones (e.g. QHY5LII-M) will get the job done, but larger pixels and lower noise (e.g. asi174mm mini) are more pleasant to work with.  The 290 is a good compromise and seems to be most popular.  Get a 30-50mm guide scope for use with Hyperstar, and use that with the same guide cam.  If your SCT came with a finder scope you could probably use that.

Yea, I have a 9 X 50 finder scope. But wouldn’t I also need some type of focuser & an adapter to connect camera?

 

Also uve actually experienced the benefits of OAG over attached autoguider scope?

[bobzeq25]

Yea, I have a 9 X 50 finder scope. But wouldn’t I also need some type of focuser & an adapter to connect camera?

 

Also uve actually experienced the benefits of OAG over attached autoguider scope?

DO NOT connect the guidescope to the mainscope with a finder shoe.  Use 2 spaced rings to triangulate the load.  How they build houses and bridges.

 

Using a finder shoe might work.  Or it might cause you a nasty problem that's very hard to diagnose.  Hours of wasted and frustrating time.  Mount the guidescope securely, and stop the problem before it starts.

 

Should you choose to ignore me, the symptom is that your guiding is great (the guidescope is doing just fine), but your stars are mediocre because the mainscope is not following _precisely_.  You can't notice the flexibility with your hand, it's too small.  It only shows up in the images.

 

Several good setups here. 

 

https://www.cloudyni...ardrails/page-4

Edited by bobzeq25, 26 January 2023 - 07:15 PM.

[rkinnett]

Yea, I have a 9 X 50 finder scope. But wouldn’t I also need some type of focuser & an adapter to connect camera?

 

Also uve actually experienced the benefits of OAG over attached autoguider scope?

I can't remember which thread type my Celestron finder scope had, but it was easy to find a combination of adapters and spacers in the box of miscellaneous small black parts.  The front lens cell gives you fine focusing control if you want to mount your camera rigidly, or you use a clamping interface on the camera side or a helical focuser.  Should be lots of ways to make it work.

 

Yeah, I experimented with guiding SCTs with guide scopes for a few years before trying an OAG.  The OAG took more time to figure out, but once I got it dialed I was blown away at the improvement in my imaging.  It was like putting on a pair of glasses.  I think lots of folks here have gone through the same progression.  The main advantage of using an OAG is that your guiding scale roughly matches your imaging scale, due to both being at the same focal length, whereas with a guide scope you typically end up with a guiding scale of 3-5x your imaging scale and that translates to more blur in your images.  Guide scopes are also prone to flexure which further blurs your images, and all that extra weight (many pounds more compared to an OAG) makes your whole system more prone to vibration and stiction effects.  To guide an 8" SCT at f/7, you would need at least 350mm focal length.  ST80s are pretty common for guiding up to 10" SCTs, but that's an awful lot of weight, especially if you mount it properly with a rail and guide rings.  And since you're on an az/el mount on a wedge, you would need counterweights on the underside of your SCT to balance the big guide scope.  The most common complaints about OAGs are that it takes a bit more learning to figure out, and it can be hard to find guide stars.  The guide star selection problem is real on some targets, but not most.  I think I had to give up on maybe one target out of a couple dozen.  Trouble is, it's usually the small galaxies away from the ecliptic that you really want to shoot with an SCT that have the fewest bright guide star candidates nearby.

[John_robertson1953]

I can't remember which thread type my Celestron finder scope had, but it was easy to find a combination of adapters and spacers in the box of miscellaneous small black parts.  The front lens cell gives you fine focusing control if you want to mount your camera rigidly, or you use a clamping interface on the camera side or a helical focuser.  Should be lots of ways to make it work.

 

Yeah, I experimented with guiding SCTs with guide scopes for a few years before trying an OAG.  The OAG took more time to figure out, but once I got it dialed I was blown away at the improvement in my imaging.  It was like putting on a pair of glasses.  I think lots of folks here have gone through the same progression.  The main advantage of using an OAG is that your guiding scale roughly matches your imaging scale, due to both being at the same focal length, whereas with a guide scope you typically end up with a guiding scale of 3-5x your imaging scale and that translates to more blur in your images.  Guide scopes are also prone to flexure which further blurs your images, and all that extra weight (many pounds more compared to an OAG) makes your whole system more prone to vibration and stiction effects.  To guide an 8" SCT at f/7, you would need at least 350mm focal length.  ST80s are pretty common for guiding up to 10" SCTs, but that's an awful lot of weight, especially if you mount it properly with a rail and guide rings.  And since you're on an az/el mount on a wedge, you would need counterweights on the underside of your SCT to balance the big guide scope.  The most common complaints about OAGs are that it takes a bit more learning to figure out, and it can be hard to find guide stars.  The guide star selection problem is real on some targets, but not most.  I think I had to give up on maybe one target out of a couple dozen.  Trouble is, it's usually the small galaxies away from the ecliptic that you really want to shoot with an SCT that have the fewest bright guide star candidates nearby.

Hi I’m interested in further pursuing possibility of reconfiguring my finder scope into an

autoguiding scope, and attaching a camera.

I’ve read the various pro/cons of scope mounts, but I have to tell you, the mount that came with the finder is very sturdy, much like the auto align star sense mount I use. Don’t have much to lose, only the cost of reconfiguring the finder scope. You mention box of misc small black parts. What are u referring to, something I can purchase?  Or has someone done this & can detail parts, adapters, etc to make this conversion?  Same goes with focuser- is one really needed?  When I’ve used as a finder, resolution was fine.
One other question I have, if this is a workable solution, could I use this reconverted finder/ guiding scope and camera with both the .7Xreducer and the hyper star?  Or is this just to be used for the hyperstar?  Reducer would require min 350 mm FL per ur comment above, where I believe 9X50 scope is only 160-190mm?

Thanks for your help. It’s really appreciated. 

Edited by John_robertson1953, 27 January 2023 - 02:29 PM.

[lancing]

Hi I’m interested in further pursuing possibility of reconfiguring my finder scope into an

autoguiding scope, and attaching a camera.

I’ve read the various pro/cons of scope mounts, but I have to tell you, the mount that came with the finder is very sturdy, much like the auto align star sense mount I use. Don’t have much to lose, only the cost of reconfiguring the finder scope. You mention box of misc small black parts. What are u referring to, something I can purchase?  Or has someone done this & can detail parts, adapters, etc to make this conversion?  Same goes with focuser- is one really needed?  When I’ve used as a finder, resolution was fine.
One other question I have, if this is a workable solution, could I use this reconverted finder/ guiding scope and camera with both the .7Xreducer and the hyper star?  Or is this just to be used for the hyperstar?  Reducer would require min 350 mm FL per ur comment above, where I believe 9X50 scope is only 160-190mm?

Thanks for your help. It’s really appreciated. 

I'm kind of the same opinion of the riknnett, if you are using an Nexstar or Evo mount with a wedge its going to make long duration guiding harder. I'd expect precise OAG guiding will be near impossible for any sustained period of time at the SCT's native focal length.

 

Your mount is not stable enough so every time it wobbles its going to feed constant unexplained guiding errors into PHD2 which PHD2 is going to try and compensate for assuming its a problem with your mount motors, gearing or alignment. That problem is going to stack and get worse over time until you guiding will just go all over the place.

 

The focal reducer screws into the back of the SCT where your visual train attaches. Its just a lens element that screws on.

 

You can image with your current mount but you'll need to keep your exposure times down.

 

I have a C8 with a focal reducer which I image with using a 50mm guide scope but its mounted to an AVX and everything is locked properly with screws. Its fine for imaging with the focal reducer but I seriously doubt I could do any type of longer exposures at the SCT's native focal length.

Edited by lancing, 27 January 2023 - 04:07 PM.

[flightlogic]

following this thread with interest.... and I know my question probably belongs elsewhere.  I suspect you guys will have a quick thought.

If I bolt a guide camera to the 8SE, does it have to be aligned closely with the object being viewed?  As a finder would be adjusted to see exactly the same object...

Or, is roughly parallel to the SCT tube ok... does it all come out in the wash, as the scope corrects while tracking?

[lancing]

following this thread with interest.... and I know my question probably belongs elsewhere.  I suspect you guys will have a quick thought.

If I bolt a guide camera to the 8SE, does it have to be aligned closely with the object being viewed?  As a finder would be adjusted to see exactly the same object...

Or, is roughly parallel to the SCT tube ok... does it all come out in the wash, as the scope corrects while tracking?

The guide scope absolutely needs to be rock solidly connected to the main scope. There can not be any play or give on it. This is also why having a stable mount is so critical for imaging.

 

PHD2 does not like unexplained wobble or drift in its tracking. PHD2 generally monitors its tracking performance and will try and compensate for PEC, motor behavior, or alignment issues by predicting them out. Its not good at dealing with random mount or scope wobble. In some extreme cases if it gets bad enough the tracking will just completely drift off target and not work.

 

You don't absolutely need overlapping fields of view but that can make life easier at times since you'll always know what the guide scope is actually looking at in terms of guide stars.

 

The usual rule of thumb is you want your guide scope to be at least 1/3rd the focal length of the main scope. Like all rules there are some exceptions to this.

 

OAG's generally guide better on SCT's then a dedicated guide scope but are more difficult to setup. But they are even more sensitive to any type of mount or scope instability.

 

For two guide cameras with the same sensor mono is usually the best option.

Edited by lancing, 29 January 2023 - 10:16 AM.

[flightlogic]

CLARITY... a favorite of mine in life.  Thanks Lancing!

[John_robertson1953]

Yea, I have a 9 X 50 finder scope. But wouldn’t I also need some type of focuser & an adapter to connect camera?

 

Also uve actually experienced the benefits of OAG over attached autoguider scope?

Was getting ready to pull the trigger on a Celestron OAG and was reading about incompatibility, so I decided to contact Celestron support and they responded:

 

“Thank you for contacting Celestron Technical Support.

We generally do not recommend the Celestron OAG with the EdgeHD 8 0.7x reducer for two reasons:

1) With the image circle restricted to 28mm, it is hard to get the large prism low enough to catch light from the reducer without casting a shadow on the imaging sensor. You can make this work with a smaller sensor (the ASI294MM might work), but one side of the prism will be noticeably more vignetted than the other. If your ideal prism placement does cast a shadow on your sensor, you can correct this only with very accurate flat frames.

2) With the 8" Reducer, the back focus is reduced from the normal 133.35mm to 105mm. The adapters that come with the 93648 OAG are designed to work at 133.35mm, so custom adapters will likely be needed to precisely hit the shorter 105mm back focus. https://www.precisep...ain//index.html can build such an adapter, but they can be pricy. A 0.0mm effective length adapter from the reducer to the OAG body would run a couple of hundred dollars.

Neither of these issues are necessarily a deal breaker, but they do add additional complexity to the equation and can compromise imaging performance. Because of this, we do not recommend this OAG for the f/7 reducer on the 8" EdgeHD.

Celestron Technical Support”

 

Has anybody had any luck with any other OAG or TOAG brand?