Guidescope and camera

[George Gearless]

Hey all.

I don't think I have fully grasped the workings of the guidescope. So I'm trying to get some clarity here.

Here is my current understanding of how it works:

You mount your guidescope piggyback on your primary telescope which is on a properly aligned EQ mount. With your primary scope, you find the object you want to photograph. You then adjust your guidescope on a single star and it 'latches on' the star. If the star, and thus your primary telescope, moves off track, the guidescope sends corrections to your mount to center it once again. I know this is terribly simplified, but am I right so far?

I have seen setups where the guidescope is a monstrosity with an aperture and length that rivals that of the primary telescope. Why? If the guidescopes only purpose is to keep a targeted star in the center, why can't you use that flimsy plastic finderscope with acrylic lenses that you bought for a fiver? 

The camera: Ofcourse you need a camera to 'see/register' the star you are tracking. I pressume some software and a laptop is also required to tie the whole thing together. I've perused various sites and typed in "autoguider" or "guidecamera" in their search engines. A multitude of cameras are found. Ranging from €120 to the thousands. The very expensive ones seem to be able to double as an actual camera for planetary or even deepsky photography. But for my purpose, using a DSLR as my main camera, the dual purpose is uninteresting. The question is; are the very expensive cameras 'better' (as in more accurate or whatever) as autoguiders, or is the difference in price primarily due to their ability to also function as an actual AP camera?

Oh and btw; is there a distinction between an 'autoguider' and a 'guidingscope with a guidecamera'. Or are they essentialy the same things?

Hope someone can clear this up for me.

 

George

 

 

 

 

[Davey-T]

You've got the general idea all right.

A guide camera doesn't need to cost the earth, something like a QHY5, mono is recommended.

 The guide scope which can really be any small refractor you've got handy, the Sky Watcher ST80 is a favourite.

The most important thing is that the guide scope is fitted rigidly to the main scope, any flexure between the two will play havoc with your guiding.

Most folk use PHD to guide connected to a laptop.

There are some stand alone autoguider cameras with a LCD display that don't need a computer connected but I wouldn't recommend one.

Dave

[Klitwo]

[George Gearless]

1 hour ago, Davey-T said:

You've got the general idea all right.

A guide camera doesn't need to cost the earth, something like a QHY5, mono is recommended.

The most important thing about the guide scope which can really be any small refractor you've got handy, the Sky Watcher ST80 is a favourite.

The most important thing is that the guide scope is fitted rigidly to the main scope, any flexure between the two will play havoc with your guiding.

Most folk use PHD to guide connected to a laptop.

There are some stand alone autoguider cameras with a LCD display that don't need a computer connected but I wouldn't recommend one.

Dave

Thanks Dave. Glad that I've grasped at least the basics.

I'm not on the verge of purchasing an autoguider. As a newbie, I still have a lot of exploring to do with my Skywatcher AZ-Gti go-to mount and my 127 mak and my 6.1 Mpixel Nikon DX40. But I recently took my first photo of M43 and was absolutely delighted with what could be achieved with relatively modest equipment. Spured on by my 'success' I'm pretty sure I've got the AP bug in my system now. And so the search for "bigger and better" has begun. I'm sure you and many others in this forum can relate :).

Without making any commitments (it's financialy not feasible right now because I'd also need a new mount), I've browsed around the website of my most trusted equipment-pusher and found a scope and a camera that I think would suit my needs . I'd like your input as to this combination: ToupTek Camera G-1200-KPB Color Guider and Skywatcher Guidescope Evoguide 50ED . If anyone has had actual experience with either, I'd very much like their input as well.

George

 

[vlaiv]

That camera is perfectly fine (as long as it has decent drivers and software support) - as it is the same sensor as in very popular QHY5LII and ASI120.

I'm sure guide scope is also fine (I have not used that particular model), but I'm slightly worried about possible differential flexure.

I used to guide with similar combination - QHY5LII and this guide scope:

https://www.teleskop-express.de/shop/product_info.php/info/p7073_TS-Optics-Deluxe-60-mm-Guiding-Finder-scope-with-micro-focusing.html

60mm - so a bit more light grasp but same focal length as Evoguide, and the same mounting type. I had differential flexure. It was not bad, and I was able to work with 1-2 minute exposures fine with it, but if I look at all the frames in multi hour session - there would be quite a bit of movement between first and last sub (about 20-30"). This won't be a problem if you are using shorter exposures - and it acts as "natural" dithering, but something to consider if planing longer exposures than about 2 minutes.

One more consideration would be guide resolution. This is something that you need to think of if going into high resolution imaging (large focal lengths and small pixel scales) with serious mount. You need enough precision in star position to be able to guide very precisely. 240mm of above guide scopes is not enough for that, and best solution in those cases is to go with OAG - or off axis guider. It uses main scope for guiding as well as imaging, so you don't have two separate scopes and you don't need to worry about any differential flexure. Another benefit is that you are guiding at same focal length as you are imaging - so you have enough precision for guiding.

But like I said, you don't have to worry about those things now, above is sufficient for your needs at the moment.

[George Gearless]

1 hour ago, vlaiv said:

That camera is perfectly fine (as long as it has decent drivers and software support) - as it is the same sensor as in very popular QHY5LII and ASI120.

I'm sure guide scope is also fine (I have not used that particular model), but I'm slightly worried about possible differential flexure.

I used to guide with similar combination - QHY5LII and this guide scope:

https://www.teleskop-express.de/shop/product_info.php/info/p7073_TS-Optics-Deluxe-60-mm-Guiding-Finder-scope-with-micro-focusing.html

60mm - so a bit more light grasp but same focal length as Evoguide, and the same mounting type. I had differential flexure. It was not bad, and I was able to work with 1-2 minute exposures fine with it, but if I look at all the frames in multi hour session - there would be quite a bit of movement between first and last sub (about 20-30"). This won't be a problem if you are using shorter exposures - and it acts as "natural" dithering, but something to consider if planing longer exposures than about 2 minutes.

One more consideration would be guide resolution. This is something that you need to think of if going into high resolution imaging (large focal lengths and small pixel scales) with serious mount. You need enough precision in star position to be able to guide very precisely. 240mm of above guide scopes is not enough for that, and best solution in those cases is to go with OAG - or off axis guider. It uses main scope for guiding as well as imaging, so you don't have two separate scopes and you don't need to worry about any differential flexure. Another benefit is that you are guiding at same focal length as you are imaging - so you have enough precision for guiding.

But like I said, you don't have to worry about those things now, above is sufficient for your needs at the moment.

Good input.

Time is fortunately on my side before making any final decisions. I'll certainly be looking into off axis guider. Something I would not have considered, had you not mentioned it. Or at the very least make every effort to secure the guidescope rigidly, as Dave also stressed in his post.

Thanks.