Guidescope Alignment Question

[feilimb]

Apologies if this has been asked & answered many times before.  I am entering the world of imaging and will be going on a first light session hopefully this week (if the skies behave).  In the past few months I have picked up (but not yet used out in the field) - Orion 50mm guidescope & HEQ5 Synscan mount.  I have just been using the mount for visual since I invested but hope to start imaging soon.  

My focal length is a bit on the high side for a beginner 8" SCT with f6.3 reducer - so I'll be imaging at around 1280mm @ F6.3 .

For autoguiding this is probably hitting the limit of capability for the focal length of the 50mm guide scope but I'd like to give it a try.  I am wondering how close the alignment of my guidescope should be with respect to the alignment of my imaging scope.  Is there a decent margin of error (eg. of less than or more than 1 degree etc?), or should I really spend time trying to align the centre point of the guide-scope's FOV with centre-point of the imaging scope's FOV?

At the moment I can't mount both the guide scope and a finder scope, and I find it difficult to align guidescope with the main scope - when I insert an eyepiece into the guide scope I can't achieve focus unless I pull the eyepiece so far back that it is not actually in the guide-scope anymore, even with a small extension tube.

[Uplooker]

You are right about making things difficult for yourself imaging at such a long FL but do not worry too much about alignment of the imaging and guide scope. As long as the guide scope is pointing in roughly the same area of the sky and you be fine. It always surprises me when people spend a lot of money on fancy mansy guide scope mounts, I think they just add more chance of differential flexure.

It seems to be best, when imaging at a long FL, to use an OAG. Maybe something to save up for in the future

[Anne S]

18 minutes ago, feilimb said:

 

At the moment I can't mount both the guide scope and a finder scope, and I find it difficult to align guidescope with the main scope - when I insert an eyepiece into the guide scope I can't achieve focus unless I pull the eyepiece so far back that it is not actually in the guide-scope anymore, even with a small extension tube.

I have a finderguider set up on the finder shoe. I use a Rigel red dot finder to check scope pointing, mounted between the tube rings. I can then slew to a bright star, hopefully it'll be in the camera chip once I've centred it. I chose the Rigel because of lack of space, you may have room for a Telrad.

Anne

[feilimb]

Thanks Ian and Anne for your input - I had totally forgotten about the OAG option. I have read of the frustrating experiences other people have had using them over the years and I'm not sure if they are for me, but it's something I might consider if all else fails with the guide scope.

Thanks Anne, in my case I don't have tube rings, just some radial blocks and a dovetail bar to get the scope onto the mount head.  There's probably some other solution to get eg. the red dot finder and the guide scope on an SCT at the same time, I should look into this!  I'll keep you all posted if I ever get to the point of capturing some image data  

[ollypenrice]

21 hours ago, Uplooker said:

You are right about making things difficult for yourself imaging at such a long FL but do not worry too much about alignment of the imaging and guide scope. As long as the guide scope is pointing in roughly the same area of the sky and you be fine. It always surprises me when people spend a lot of money on fancy mansy guide scope mounts, I think they just add more chance of differential flexure.

It seems to be best, when imaging at a long FL, to use an OAG. Maybe something to save up for in the future

Inronically the point of the 'fancy mancy'  guide scope adjusters is not to align the guidescope but to do precisely the opposite. Guide rings and other adjusters were invented to allow the user to search for a guide star by moving the guidescope around. When we were guiding by eye or with the early, low sensitivity, autoguiders we needed to do this. Now there is no need at all to do so.

While a guidescope does not need to be aligned (which is proven by the original use of adjusters and guide rings) there is a small caveat. If you are not perfectly polar aligned the centre of field rotation will be the guide star. If this is a long way from the image then the effects on long exposure will be more severe. If the guide star is central to the image then that will be the centre of any field rotation. It will be less intrusive that way. But with good PA, it won't matter.

Olly

[SonnyE]

I'm more of one to like everything aimed the same place. I've spent several sessions towards that goal.

I began with getting my main telescope on Polaris as my general target, because it moves so slowly.

Then aiming my guide scope by adjusting the screws very gently on my Orion Guide Scope. Also trying to get the guide scope to where the controller arrows move an object along the same lines as the display. (Within reason) Getting the "picture" in PHD2's view to be accurate is important to me because I use that view as my eyepiece during my alignment. So you are beginning to see why I like things all hitting the mark...

I also use a Red Dot sight for my course aiming. And want that aimed correctly as well. (I also have a green laser, but that is to simply guide inquisitive eyes toward the target, not for aiming.)

But having my guide scope centered as close as possible to my main optical tube's aim works for me. For me, accuracy counts. Regardless of what guide star PHD2 picks.

[dhickey]

23 hours ago, feilimb said:

Apologies if this has been asked & answered many times before.  I am entering the world of imaging and will be going on a first light session hopefully this week (if the skies behave).  In the past few months I have picked up (but not yet used out in the field) - Orion 50mm guidescope & HEQ5 Synscan mount.  I have just been using the mount for visual since I invested but hope to start imaging soon.  

My focal length is a bit on the high side for a beginner 8" SCT with f6.3 reducer - so I'll be imaging at around 1280mm @ F6.3 .

For autoguiding this is probably hitting the limit of capability for the focal length of the 50mm guide scope but I'd like to give it a try.  I am wondering how close the alignment of my guidescope should be with respect to the alignment of my imaging scope.  Is there a decent margin of error (eg. of less than or more than 1 degree etc?), or should I really spend time trying to align the centre point of the guide-scope's FOV with centre-point of the imaging scope's FOV?

At the moment I can't mount both the guide scope and a finder scope, and I find it difficult to align guidescope with the main scope - when I insert an eyepiece into the guide scope I can't achieve focus unless I pull the eyepiece so far back that it is not actually in the guide-scope anymore, even with a small extension tube.

For what it's worth, I'm using a Meade 8" SCT with an f/6.3 reducer, Orion 50mm guidescope, Starshoot Autoguider, and an Orion Atlas Pro mount.   I have not had any trouble with guiding out to about 6 minutes so far.  I have the guidescope only roughly aligned such that the object I'm looking at with the SCT is at least within the FOV of the guidescope, but I haven't found it necessary to try to get them perfectly aligned.  I have not tried removing the reducer and imaging at f/10 yet, although I'll be trying that soon. 

If the 50mm doesn't cut it at f/10, I have an 80mm Orion ST80 that's currently riding piggy-back that I'll try.  My original setup last year was trying to use the ST80 as a guidescope but didn't work at all.  I think it had more to do with the original LX50 fork mount from 1999 than anything else.  It will be interesting to give that a try again now that it's riding on the Atlas Pro mount.

Dave

[ollypenrice]

On 21/03/2017 at 17:22, SonnyE said:

I'm more of one to like everything aimed the same place. I've spent several sessions towards that goal.

I began with getting my main telescope on Polaris as my general target, because it moves so slowly.

Then aiming my guide scope by adjusting the screws very gently on my Orion Guide Scope. Also trying to get the guide scope to where the controller arrows move an object along the same lines as the display. (Within reason) Getting the "picture" in PHD2's view to be accurate is important to me because I use that view as my eyepiece during my alignment. So you are beginning to see why I like things all hitting the mark...

I also use a Red Dot sight for my course aiming. And want that aimed correctly as well. (I also have a green laser, but that is to simply guide inquisitive eyes toward the target, not for aiming.)

But having my guide scope centered as close as possible to my main optical tube's aim works for me. For me, accuracy counts. Regardless of what guide star PHD2 picks.

If it makes you feel better, do it. But it's a bit like levelling mounts. If you are polar aligned it has absolutely no significance whatever. 

Olly

[SonnyE]

6 hours ago, ollypenrice said:

If it makes you feel better, do it. But it's a bit like levelling mounts. If you are polar aligned it has absolutely no significance whatever. 

Olly

It comes from my 42 years in the Electrical Industries. Doing my best at anything I'm doing.

Less than the best causes things to blow up at that level. And could take a life.

So it had a great deal of significance. I like to err on the careful side.

To each his own.

[feilimb]

Folks thanks so much for all the really valuable input, I learned quite a bit just from this thread (I had not previously realised that if polar alignment was done with guide scope, which may not be aligned with imaging scope, then field of rotation will be on guide star).  I have since managed to connect an old finderscope alongside the guidescope, and last night managed to get the mount scope roughly polar aligned, and QHY5 camera up and running in the guide scope, with control of the mount via EQMod.  

My next step will be trying to get the Canon 450d talking to my laptop and mounted on the main scope..  Thanks again to all for the input!

[Thalestris24]

Hi

It's worth bearing in mind that when you Polar Align, by whatever method, it's the mount you are aligning. It's the mount that you adjust (DEC and RA) in order to get aligned. I would imagine that if you have an oag, then as the guide cam will be getting it's star image via your imaging scope, you should be able to get the most precise PA if you use, say, PHD2 to do the drift aligning. I've no personal experience with an oag though  Probably you'll be able to manage ok with a guide scope.

Louise

[SonnyE]

23 hours ago, feilimb said:

Folks thanks so much for all the really valuable input, I learned quite a bit just from this thread (I had not previously realised that if polar alignment was done with guide scope, which may not be aligned with imaging scope, then field of rotation will be on guide star).  I have since managed to connect an old finderscope alongside the guidescope, and last night managed to get the mount scope roughly polar aligned, and QHY5 camera up and running in the guide scope, with control of the mount via EQMod.  

My next step will be trying to get the Canon 450d talking to my laptop and mounted on the main scope..  Thanks again to all for the input!

I found that at best Polar Alignment of the mount is rough. Meaning looking through a polar alignment scope mounted it the bowels of the mount gets one started. But is not the end all, be all, of our mounts mechanical alignment. It is a starting point.

After doing an alignment where 6 stars are aligned to, I do Celestron's All Star Polar Alignment to check and correct any mechanical errors. Because I know that my mount sitting outside 24 hours a day is going to slightly move from temperature swings, or Earth vibrations. So tiny changes are needed to adjust the mount back to get the kind of guiding I desire for my imaging means.

And if I remember correctly, the Orion 50 mm guide scope is supposed to be good up to a 1500 mm telescope. So you would be fine for your telescope.

You might want to read up on Periodic Error Correction as well. That is yet another method where the error in our mounts drive trains is compensated for in the electronics driving the scopes movement to track celestial points.

Polar Alignment, Mount Alignment, Fine adjustment PA (or ASPA), PEC, and then slewing to your target, centering up, focusing... and you are ready to go! Nothing to it.

The more you do it, the easier it gets. In fact, doing alignments has taught me a lot of my skies geography. I can look up at most any given time and identify stars because of my aligning. It isn't all scary and mysterious, it's a lot of fun. And these Go-To mounts are wonderful, once you get some time under your belt with them.

And the guide scope... that is the eye for the mount to know where it is, and what it needs to follow, for your wondering eyes.