good guidescopes

[nobbygon (Angus)]

Hey everyone,

What are some good guidescopes out there in the 60 - 70mm range?
I'm looking for something with a solid focuser too.
Cheers for the help,
Angus

[GrampianStars (Rob)]

http://www.astronomics.com/main/prod...duct_id/AT72BK
AT72 doublet

[nobbygon (Angus)]

Can you get that in Australia?

or do you have to get it imported direct from astronomics?

[ballaratdragons (Ken)]

Hi Angus,

it might sound strange but you can use almost any cheap el-crappo telescope as a guide scope.

Many people even use a finderscope.

A Guidescope does not need to be optically excellent. Nor does focus need to be sharp, which is actually a benefit as guide stars work better if they are slightly out of focus.

The only thing I would suggest is don't go any slower than about f7
The faster the better. Some cheap achro's are available around f5

I've even seen people guiding with $50 scopes picked up at Garage sales for $10

[tlgerdes (Trevor)]

I run one of those Orion 80mm F5 acro's, finds guide stars easliy.

[nobbygon (Angus)]

Great, thanks for the help.

Glad to hear that a guidescope doesn't have to be high quality.

How good does the focuser have to be? I've read that if its poor quality you can get flexure limiting the max length of subs.

Thanks for all the help.

[ballaratdragons (Ken)]

Originally Posted by nobbygon

How good does the focuser have to be? I've read that if its poor quality you can get flexure limiting the max length of subs.

That would only be of concern in the 'imaging' camera.
You don't take subs with a guiding scope and camera.

[jjjnettie (Jeanette)]

I use my little f5 80mm iOptron for guiding. The optics are ok on it, but
the focuser had to be replaced because of slop.
I always use a focal reducer with the QHY too, so I have a wider range of guide stars to choose from.

[tlgerdes (Trevor)]

Not quite true Ken, the focuser on the guidescope is just as important. Differential flexure is the primary concern here. If you have movement in you guidescope focuser, your guidestars can "move" and throw your guiding out the window.

[ballaratdragons (Ken)]

Originally Posted by tlgerdes

Not quite true Ken, the focuser on the guidescope is just as important. Differential flexure is the primary concern here. If you have movement in you guidescope focuser, your guidestars can "move" and throw your guiding out the window.

I'm not talking about a floppy focuser here!
Of course we want everything as a nice solid fit or it is just junk.

I read Angus's comment as if he was thinking that the image Subs are taken with the guidescope.

[Irish stargazer (John)]

I have started using a Megrez 72 for guiding my C11. I also use the C11 as a guide scope for the Megrez as it is a fine astrograph. Its nice to be able to use them either way depending on the object or conditions just be switching over the main and guide cameras.

[RobF (Rob)]

Standard skywatcher 9x50 finder with an Orion Starshoot Autoguider in the back is the best guider (and e-finder) I've ever used. Cost me $30 2nd hand I think - I didn't want to hack around with my main finder

I think camera, then software, then mounting comes before money invested in the scope. I'm ducking down now.....

[gregbradley]

I have used the AT66Ed which is the earlier model to the AT72ed.

Overall very good. I do get some differential flexure. But if I limit exposures to 10 minutes it isn't a problem but it does limit the length of exposures.

I use a diagonal so I can get to focus. Perhaps that adds to flexure.

Focuser is good not perfect. It can lack grip and slide if not tightened.

Also the focuser has a rotator which could add flex. Try to keep it tightened up as well.

But I can always get a guide star and 10 minutes at 1260mm gives round stars so its pretty good.

I mount it using 2 Losmandy D adapters which fit onto a dovetail plate on top of my refractor.

Its a workable system but limited.

Offaxis guiders are fussy but give better results as they don't suffer from flexure.

If you are using short focal length you can use a camera lens or an SBIG Efinder and fix the camera and efinder to the front section of the OTA's dovetail plate. That works too but probably only for short focal length.

AP sell a 900mm "cheapish" refractor and rings as a guidescope. No doubt it would be a good setup.

I bought a Vixen 95LMC as a guide scope as that is 1000mm focal length. Problem was I had trouble finding guide stars. Perhaps the 110mm LMC may be better as it has a bit more aperture. These are quite light and relatively inexpensive.

Greg.

[Geoff45 (Geoff)]

Originally Posted by ballaratdragons

That would only be of concern in the 'imaging' camera.
You don't take subs with a guiding scope and camera.

If the focuser of the guidescope flexes, then the mount will adjust to bring the star back to centre and the image in the main camera will be trailed, so yes, the focuser is an issue for the guidescope.
The Orion short tube 80mm at just over $200 is a reasonable choice.

[ballaratdragons (Ken)]

Originally Posted by ghsmith45

If the focuser of the guidescope flexes, then the mount will adjust to bring the star back to centre and the image in the main camera will be trailed, so yes, the focuser is an issue for the guidescope.
The Orion short tube 80mm at just over $200 is a reasonable choice.

Geoff, I think I am being slightly misunderstood here.

No, I don't mean a guidescope can have flop, wobble, or be crap.
I already said I thought the OP was mistaking the guide camera as an imager.

Obviously a guide camera has to be mounted rock solid. It would be pointless if it moved.
But it doesn't have to be in Focus to guide. It is better if it is slightly out of focus.

And that a guidescope can be a basic cheap achro or finderscope. It doesn't need to be an expensive high quality scope.
That's what I am, saying.

[gregbradley]

"But it doesn't have to be in Focus to guide. It is better if it is slightly out of focus."


I have heard that idea before. I am not sure that is true.

I have found I get lower guide errors when the guide stars are sharply in focus. As the software calculates the centroid of the star, it seems to me it would be a more accurate computation if the bright central area is smaller than if it were larger.

Also, I find with autoguiding that if I get larger than expected guide errors, simply picking another tighter looking star gives instant improvements.

Also, often guide stars are double stars. If they are a bit out of focus they will look ellipsoid in shape. This would have to mean an inaccurate computation of the centroid as it is an ellipse not a circle. It certainly is good practice not to pick a double star as a guide star nor a guide star that has another brighter or similar brightness star nearby that could confuse the software.

Another point as well is sometimes when guiding you get a brief cloud getting in the road. A well focused star is more likely to shine through a partial cloud cover than an out of focus one.

What have you found with regards to having guide stars slightly out of focus and what is the theory about that?

This is an interesting thread. I'd like to hear what guidescopes people are using that they are happy with.

I suppose the requirements are:

1. wide enough field to be able to pick up guide stars easily. Also to have the guide stars bright enough to be useable.
2. Nice solid and easy to use focuser. No slop or too large an opening. The eyepiece holder has solid and powerful locking screws or compression rings so
you don't get a rocking motions.
3. Long enough focal length to give accurate guiding but not so long as to make it hard to pickup a guide star. Not sure about the ideal focal length
here - I'd love to hear what others say about this. AP's guide scope is 900mm and about 60mm aperture or so. I assume that is considered by them
to be ideal. Too high an F ratio is probably not a good thing either as guide stars become too dim and harder to find.
4. It has to be light and easily mounted.
5. No flex in the rings or the focuser or the rotator if it has one. Enough backfocus to be able to mount a guide cam without extension tubes.
6. Not too expensive.

The little AT66ED that cost US$200 2nd hand fufills the above quite well except for focal length as I think its only about 340mm or so. But as I say the Vixen 95LMC
with nearly 1 metre focal length was very hard to use as I had trouble finding a guide star. It is also F10 I think.

Greg.

[RB (Andrew)]

Originally Posted by nobbygon

Hey everyone,

What are some good guidescopes out there in the 60 - 70mm range?
I'm looking for something with a solid focuser too.
Cheers for the help,
Angus

I use an Orion Short Tube 80 with an Orion StarShoot Autoguider using PHD.
I've never had a problem with them.
The scope holds the guider perfectly and I even have an Orion XY Guidestar Finder on there too..

Just make sure you mount the guidescope as solidly as possible.
Good solid mounting rings, don't use the adjustable screw type guidescope rings.

[nobbygon (Angus)]

I ordered the losmandy 108mm VR guidescope rings. Should they be ok?

[mswhin63 (Malcolm)]

I was considering getting a guidescope for my DOB. Yes a guidescope for my DOB but I want to look at using the guide scope for widefield. I would interchang the DOB as a guidescope when doing widefield or visa versa. Obviously would need a good guide scope.