Round stars using a guidescope at 1000mm - possible?

Provided you have a stable base for the mount and a mount with sufficient load-bearing capacity for the telescope, it is no problem to obtain round stars with a guidescope at 1000 mm focal length. 50 mm and 60 mm guidescopes with focal lengths of 180 mm and 260 mm are no problem with my 130/910 mm refractor. If there have been oval stars across the entire field of view, it was always due to a differential movement between the telescope and the guide scope. The cause was either insufficient attachment of the guide scope or cable pull on its camera or dew strip.

Pete

I’m imaging with an AT130mm EDT.

Probably similar in weight to your ZWO. My rig from the clamp up currently is 36 pounds which likely includes more weight than yours. I’m using an Svbony 106 60mm guide scope piggy-backed with my main telescope.

One stark difference is your guide camera. I’m using an ASI290MM Mini.

Which I think mine was one of the last 2.9um X 2.9um they sold, because the same week ZWO came out with the 220 which has a courser sensor. And I chose mine over the 120 to get more pixels for finer guiding. And in real world use it has panned out in much tighter guiding steps in PHD2. (@ 1 second sampling). Seeing can affect your guiding, but mine is down in the 0.2 and 0.3 totals, so it is damned fine.

You said you took your new scope out for a test spin last night. How good was your Polar Alignment? How stable is your tripod set-up? Is it possible to leave your equipment set up for, say, weeks at a time? To give it time to settle. So often I read where someone does a quick setup, then wonders why their guiding is so marginal.

The guiding may not be as marginal as you think. It may be a combination of things fighting you. Starting with your mount not being as stable as need be for sanitary guiding.

How much does what you are mounting weigh in comparison to your mount’s capacity? Are you grossly overloading, or near its top limit (44 pounds)? How carefully have you set the balance? Often, I read where quick setting up has brought mediocre results. Changing equipment won’t compensate for sloppy practices.

That is why a pier setup can hold its PA and guiding much better than a portable mount. And why I keep my mount and equipment in a setup state on a semi-solid foundation. I explained to Scott Losmandy my goal was a Portable-Pier configuration, and he understood completely. I can’t sink a pier where I’d like my equipment to be. So my “Portable Pier” setup is the best option for me.

I suggest you explore your physical setup before you go looking at changing equipment around, throwing money at a problem isn’t a good answer. Make sure it isn’t going to be wasted.

Interested to know what most people with this kind of setup would guide with? I read somewhere that shifting the guidescope from the finder shoe at the rear of the scope closer to the front (e.g. mounted on the tube rings) might be helpful, but I don’t know how I would do that.

To answer this directly, My telescope has very similar rings as yours. I simply used the upper mounting where your handle is as my spot for a second D-bar. I have two 14” Losmandy D-bars top and bottom of my telescope rings. The bottom D-bar is of course for mounting everything in the DEC clamp. The upper D-bar is for mounting my 60mm Svbony 106 guide scope, guide camera, and my home-made 12” dew/light pollution shield. I was told my idea wouldn’t work. Wrong. It works admirably, and my guiding specs run 0.2 to 0.3 . A damsite better then the coveted 0.5.

No pictures, didn’t happen. Maybe a picture (or 2) will be better than a thousand words. But here’s a proven successful answer to your question.

📷 Equipment

https://app.astrobin.com/i/boe07s/

📷 Equipment, East side view

https://app.astrobin.com/i/m4ot9s/

There are lots of things that can cause an elongation that have already been covered. If your final stack has round stars I wouldn’t worry much about a few subs. I my experience this is very common and can be caused by a number of things. Just remove them and push on down the road. If you are loosing to much integration time by culling then shorten your sub exposure length, you won’t loose any photons.

If you are seeing star out of roundness in your final stacks that you can’t fix by culling a few subs then yes, it’s time to dig deeper. As others have mentioned, mounting your guide scope on a small shoe is asking for trouble. To minimize differential flexure you need something much more solid. You don’t absolutely need to go OAG but that is certainly one solution to the problem. My last bit of advice is don’t try to analyze the system when you’re getting poor guiding RMS numbers. Do it on a night when you are consistently near your lower figure of 0.5”

TiffsAndAstro · Feb 5, 2026, 06:54 PM

As others have said, everything feels like it's made of goo.

I liken it to an Earth made of Jello mud. 🤣

Brian Puhl:
Esprit 150 on an EQ6 and typically guide in the 0.3 to 0.4 arc second, frequently dipping in the 0.2’s on good nights.