Guidescope aperture

[Simon Dunsmore]

Hi Folks, 

Can I ask for a little more advice please? 

I've slowly been building up a astrophotography rig. Presently I have Heq5 pro goto mount with Skywatcher ED72. Camera QHY5-II. What Guidescope would suit best? I'm thinking a 50mm, ideally I'd like to fit it the finderscope shoe bracket. I see that Skywatcher do a 50mm model that is within budget. https://www.firstlightoptics.com/guide-cameras/sky-watcher-evoguide-50ed-guidescope.html

I'd appreciate your advice. 

Thanks in advance 

Simon 

[Thalestris24]

The SW 50mm finder guider scope is excellent. In general, though, it's best not to use the finder scope bracket. However, you'll probably get away with it as your imaging scope focal length is short (also depending on which imaging camera you use). You'll need an adapter to fit the guide camera to the finder. Are you thinking of using the qhy5-ll as an imaging camera or guide cam? The qhy5 is essentially a guide cam. What targets are thinking of using your setup for? 

Louise

ps I just realised you were considering the ED finder. TBH that's a bit overkill - the standard one is much better value though, as mentioned, you do need an adapter

https://www.firstlightoptics.com/finders/skywatcher-9x50-finderscope.html

Edited February 28, 2020 by Thalestris24

[Simon Dunsmore]

Hi Louise,

Thanks for the quick response. 

I'm planning on using the QHY5-II for guiding and polar alignment and a Canon 60D dslr for imaging DSOs. 

I was planning on using the finder shoe bracket because I have a Telrad mounted on the tube rings as a finder, I really get on well with that, but I guess I can remove it. 

Also, I see some guide scopes allow for alignment with the main scope and other are rigid, does that matter? 

Thanks again for your help 

Kind regards 

Simon 

 

[Thalestris24]

8 minutes ago, Simon Dunsmore said:

Hi Louise,

Thanks for the quick response. 

I'm planning on using the QHY5-II for guiding and polar alignment and a Canon 60D dslr for imaging DSOs. 

I was planning on using the finder shoe bracket because I have a Telrad mounted on the tube rings as a finder, I really get on well with that, but I guess I can remove it. 

Also, I see some guide scopes allow for alignment with the main scope and other are rigid, does that matter? 

Thanks again for your help 

Kind regards 

Simon 

 

Ok, that sounds good. It can be better to have rigid mounting to ensure there's no flex between the guide scope and imaging scope. It doesn't matter from a guiding point of view whether or not the two scopes are aligned. It may be a problem if you want to use the guide scope as an e-finder. However, using plate solving via the imaging scope is becoming a more popular way of getting on target.

Louise

[ollypenrice]

8 minutes ago, Simon Dunsmore said:

 

Also, I see some guide scopes allow for alignment with the main scope 

 

Simon 

 

In fact, they don't. The original purpose of adjustable guidescope rings was quite the reverse. Early autoguiders were of very low sensitivity and the imager would have to search for a guide star by aiming the guidesope off axis towards one. Indeed, before that there were manual guidescopes which, likewise, would be aimed towards a star on which the tormented imager would try to hold the mount by means of the keypad. Mercifully modern guide cameras will always find a star so it is better to have a rigid mounting. You do not need to align the guide and main scope.

I'm not sure why Louise is doubtful about the finder scope bracket. Some of them have only two adjustable alignment screws and a third which is spring loaded rather than adjustable. This is fine for finders but very unsuited to guidescopes. Make sure your guidescope is bolted down hard.

Olly

[Simon Dunsmore]

21 minutes ago, ollypenrice said:

In fact, they don't. The original purpose of adjustable guidescope rings was quite the reverse. Early autoguiders were of very low sensitivity and the imager would have to search for a guide star by aiming the guidesope off axis towards one. Indeed, before that there were manual guidescopes which, likewise, would be aimed towards a star on which the tormented imager would try to hold the mount by means of the keypad. Mercifully modern guide cameras will always find a star so it is better to have a rigid mounting. You do not need to align the guide and main scope.

I'm not sure why Louise is doubtful about the finder scope bracket. Some of them have only two adjustable alignment screws and a third which is spring loaded rather than adjustable. This is fine for finders but very unsuited to guidescopes. Make sure your guidescope is bolted down hard

Hi Olly, 

Thanks for your message. That explains the tube rings, thanks. 

Just to clarify, are you saying its not a good idea to use the finderscope shoe? 

Also, should I be looking for a 50mm or 60mm guidescope? There are so many out there and I've looked at so many I'm a bit baffled. 

One last question, I guess I d be best with a none rotating focuser, so as not to twist the camera wire???? 

Thank you both for your help 

Simon 

 

[tooth_dr]

1 minute ago, Simon Dunsmore said:

Just to clarify, are you saying its not a good idea to use the finderscope shoe? 

It’s ok to use the finder scope holder if you remove the flexible screw and replace with a regular bolt. 

[Simon Dunsmore]

Hi, 

Thanks. Are you referring to the retaining screw (circled) or the screw that holds the plate to the scope. This feels pretty rigid right now. 

Thanks again 

Simon 

[Simon Dunsmore]

47 minutes ago, Thalestris24 said:

Ok, that sounds good. It can be better to have rigid mounting to ensure there's no flex between the guide scope and imaging scope. It doesn't matter from a guiding point of view whether or not the two scopes are aligned. It may be a problem if you want to use the guide scope as an e-finder. However, using plate solving via the imaging scope is becoming a more popular way of getting on target.

Louise

So this is the set up right now, the scope looks pretty dwarfed by the Telrad I know! 

Still unclear, are you saying the finderscope bracket is a not a good idea? Also, 50mm or 60mm, pretty confused about the best guidescope to suit the GHY camera (that I already owned). This has an adapter with it for fitting to 1.25 opening, will I need another adapter as well???? 

Sorry for all the questions 

Simon 

[tooth_dr]

23 minutes ago, Simon Dunsmore said:

Hi, 

Thanks. Are you referring to the retaining screw (circled) or the screw that holds the plate to the scope. This feels pretty rigid right now.

No, the flexible third metal screw below

 

[Simon Dunsmore]

OK, thanks! 

[Thalestris24]

1 hour ago, Simon Dunsmore said:

So this is the set up right now, the scope looks pretty dwarfed by the Telrad I know! 

Still unclear, are you saying the finderscope bracket is a not a good idea? Also, 50mm or 60mm, pretty confused about the best guidescope to suit the GHY camera (that I already owned). This has an adapter with it for fitting to 1.25 opening, will I need another adapter as well???? 

Sorry for all the questions 

Simon 

A 50mm guide scope is fine. Most guide cams have around the same pixel sizes so a fast 50mm guide cam is great. It gives you a wide fov and bright star images. If you buy a standard finder as I linked to, you need an adapter at the rear of the finder as you have to remove the existing lens assembly viz https://www.firstlightoptics.com/adapters/astro-essentials-sky-watcher-9x50-finder-to-c-adapter.html

If you'd prefer your dedicated ED guider then you won't need that adapter. However, that guide scope has a slightly longer focal length so a slightly smaller fov. It's a personal preference which one you go for really. Btw, with a 50mm guide cam you probably won't also need the Telrad as you'll be able to use the setup as an e-finder. Which mount do you have? That's the most important part for good imaging!

Louise

[Simon Dunsmore]

Thanks Louise, 

I have an Heq5 pro goto mount. 

That all makes sense, thanks, and as long as the guidescope has a rigid fixing to the main scope all should be fine?? 

I have to admit, I am leaning towards the skywatcher Ed. 

Thanks again 

Simon 

[Thalestris24]

Just now, Simon Dunsmore said:

Thanks Louise, 

I have an Heq5 pro goto mount. 

That all makes sense, thanks, and as long as the guidescope has a rigid fixing to the main scope all should be fine?? 

I have to admit, I am leaning towards the skywatcher Ed. 

Thanks again 

Simon 

Ok - excellent mount! It's up to you which guide scope you go for. The finder-guider is maybe better value but either will do the job. Yes - flex is your imaging enemy so always strive for rigidity!

Louise

[ollypenrice]

Whether or not the Telrad will be useful depends on how you do your star alignment. For me a Telrad or finder is useful because I push my mount, not swtiched on, to an alignemnt star, switch it on, confirm that star and then go to my imaging camera. I then center the star precisely in the screen crosshair and over-ride my initial rough star alignment. However, this is not on a Skywatcher mount so your star alignment routine will be different. Still, I think a camera-free finder is often an advantage.

Olly

[Avocette]

I would mount a SW 50 Guidescope like I have on a piece of square aluminium tube suitably cut and shaped. The mounting knurled bolts are interesting - the are used in the music industry to convert from 3/8" to 1/4" UNC/Whitworth threads for microphone stands and fittings, and they do a great job locking the guidescope to the main scope mounting rings. In my case I found the finderscope base which was supplied with the Guidescope was much less solid, and placed the whole guidescope/camera too far back. The new arrangement is much better for balancing.