ST 80 or 50mm guide scope

[LouisJB]

Hi,

I've been deliberating over this for a few days, going around in circles. Seems to be pros and cons either way.

Options:

1. 50mm (finder style) guider with focal length around 160-175mm, as sold as guider scopes under various brand names. Seems more popular recently due to increased camera sensitivity, pixel sizes and better sub-pixel guiding SW

2. 80mm cheap refractor such as ST80, 400mm focal length and also used by many for guiding it seems

Some advantages/disadvantages:

1 : advantage: wide-field = more candidate stars, weight. Disadvantages: short focal length maybe not accurate for high focal length tubes?

2 : advantages: bigger objective lens, proper scope for other portable/wide-field purposes. Would guild a bigger (longer focal length) tube. Comes with many more accessories for only a small increase in price. Disadvantages: Narrower field, less candidate starts. Also heavier.

Initially I'm only guiding a small 130P (focal length 650mm, but I use a x2 so effectively 1300mm) - so probably either would be fine.

I'd like this to also work with a future tube, like a 8" astrograph, say focal length 1600mm or thereabouts.

Oh, camera = QHY5L-II (colour), for now.

Which is the better route? I'd quite like to go for option 2, but hesitate mainly due to field of view mainly. Skies where I am are not perfect but I can see to mag 5-5.5 on a good night.

Any opinions before I make an order? Thanks!

[Helite]

What mount are you putting it on?

[LouisJB]

good question! HEQ5 Pro synscan, ST-4 from camera to mount, planing to use PHD (or similar)

[Helite]

Well weight wise an ST80 should be fine from what I understand. From the information I have received on here I believe the HEQ5 can be pushed to handling a 200p/ST80 combo (heck i've had that scopes and synguider perched on my EQ5 and working reasonably)

I am biased but I would go for the ST80, just because I love that little scope and use it as a grab n go as well. Its a neat little thing and well worth the money, works great with the synguider too.

I have no experience of a finder guider, all I can do is recommend the ST80 as a great bit of kit and awesome addition to have. I am sure someone who has used both setups will be along to give better advice than I can furnish you with.

Good luck! 

[LouisJB]

Excellent info, if I don't hear too much bad against the ST80 it's likely that's what I'll go for.

What about finding stars to guide on, do you need to reposition the ST80 much if at all, and if you do you use guide rings to allow that?

I like the idea to hard mount the ST80 on a bar on top of my main tube rings to remove any flexture etc. That's only going to work of course if it generally always has stars in view to guide on.

This is my main concern - any thoughts either way?

[Crebles]

+1 for the ST-80. Cracking little scope. Took mine to Spain bubblewrapped in handluggage (with EQ1 and tripod in the big suitcase in the hold), and got some lovely holiday snaps of Sagittarius.

[Helite]

I just use the original tube rings on a dovetail then mounted straight onto the rings of the 200p. So far I have had no problem finding a guide-star with the synguider but to be fair I have not actually had much of a chance to use it. I will use it like that unless I find that I will have to get guide-scope rings, but hopefully I wont run into that issue.

[kirkster501]

I have the ST80 and echo some of the other comments.  Superb scope.  Lightweight and compact.

Be advised that to get the QHY5 to come to focus you will need a 40mm T Tube that will screw into the ST80's focuser.  Or you can use the supplied cheap barlow and take it to bits and do it that way. The QHY5 can then screw into this in turn and just comes to focus when fully racked out.  Ideally get a 50mm T Tube.

[JamesF]

Olly says he's never had problems finding stars to guide on with the ST80.  I'm not sure the "wider field of view == more stars to guide on" proposition holds true anyhow.  The ST80 will collect a lot more light than a 50mm finder given that the area of the objective is more than 2.5x greater, so whilst it may not have such a wide field of view, it will potentially show more stars in a given area of the sky.

James

[Helite]

Olly says he's never had problems finding stars to guide on with the ST80.

James

That's good to know, thank's James.

[hobsey]

I purchased the ST80 yesterday to try and mount on my 127 mak as a guide scope.

Fingers crossed it will work.

[LouisJB]

ok, that was all the convincing I needed really (some reassurance!). Looks like I'm joining the ST80 guiding club, just placed and order and for a dovetail bar to mount on top of my existing tube rings.

I'll see how I get on using the provided Barlow before deciding if T-thread extension tubes will be better.

Exciting to try this scope out and to try guiding/guided pictures!

Thanks for all the help everyone. If I remember I'll report back, while searching for info so many posts seem to fizzle on someone asking a question then not later saying what the outcome was!

[ollypenrice]

Be sure to check that everything is tight when you guide with an ST80. Check the three screws holding the rear focuser assembly into the main tube, lock the focus lock down hard, ensure that the extender and camera are tight. With this done you have a great guidescope.

Olly

[Guest]

I've got an ST80 and guide rings for sale if you want it

I use the Altair 60mm finder guider with a QHY6 now so it's redundant - but perfect for the application

PM me if you're interested but if you're anything like me you've already pressed the "Order Now" button :-)

David

[Guest]

I've got an ST80 and guide rings for sale if you want it

I use the Altair 60mm finder guider with a QHY6 now so it's redundant - but perfect for the application

PM me if you're interested but if you're anything like me you've already pressed the "Order Now" button :-)

David

Someone saw that post before they hit "Order Now" and that ST80 & Rings has a new home 

[LouisJB]

Thanks, I got a good deal on a new ST80 and rings, eyepieces etc. It's nice (and I've got it fitted on a top rail, locked down quite tight).

However the first time I went out I had trouble getting PHD to recognise stars - that's probably user error. It was windy and intermittently cloudy so I gave up and tried some unguided pictures of Andromeda. Will have a play around next time it's clear, hopefully once I've got some settings worked out (focusing onto the QHY5L etc) then I can leave it set for repeatable usage thereafter.

If I'm guiding a 650mm focal length tube with x2 Barlow to my DSLR, using the QHY5L and ST80, should I be looking to

a) defocus the stars a little for PHD

changing the default PHD guide parameters, if so any recommendations?

thanks, Louis

PS: yes I had already pressed 'order now', I was itching to make an order. The new ST80, rings, diagonal and eyepieces/barlow seems really great value for money!

[LouisJB]

Just a quick update; had the first chance to try this out last night, not for long as clouds then rain soon appeared but...

it worked! The guider and tube aren't perfectly aligned but I can work on that (for convenience, not sure it matters guiding wise) but I was able to calibrate and start guiding. Tried a 2 minute then a 4 minute test shot, stars look round, it was definitely working Not seeing thousands of guide stars, but there tended to be at least 2 or 3 decent ones, if not more.

I have no idea how to tune the PHD settings etc for optimum use in my setup, so that's something to work on next, but at least the theory has worked out (not that it shouldn't since many people use the ST80 for guiding, it's just everyone's setup is different and I wasn't sure exactly how it would pan out using the QHY5L-II sensor)

So, initial thumbs up for ST80 and QHY5L-II guiding with PHD.

Thanks for the help. Now just need some clear skies + spare time to perfect the setup and get some images. Fun!