Getting good guiding results with short exposures on ASIAIR setup - But have lots of questions….

If it works, I’m not gonna tell you to stop, but you are going to be chasing seeing pretty heavily at that speed. Generally speaking with any mount that lacks encoders, I run 1-2s exposures. Things like the AM3/AM5 with the large periodic error feature actually do decently well at 0.5 but they so heavily rely on good seeing, it’s a tough balance.

With a mount like that, getting under 1 arc second seems really good, unless you are mistakenly giving RMS in pixels. Even that is perfectly acceptable.

I would probably go with 1 second guide exposures, but the ASIAIR is not something I’m familiar with. PPEC algo on the RA axis should help quite a bit, if it’s an option on the ASIAIR.

As for the guide star, size should be the HFD, peak is the ADU value. If you’re running 8 bit mode, it will peak at 256, if you’re running 16 bit mode it will peak at 65k. You want the guide star to have a nice point to it, not a plateau. If it’s a plateau you should consider either lowering gain, or tweaking your guide star preferences.

“Good Guiding” is when your system can perform UNDER your imaging scale. Most people say shoot for 70% of your image scale. Try not to confuse this with your guide image scale, as they are two different things. We want the performance to exceed that which our main imaging camera can see. If your image scale is 2 arcsec per pixel, then ideally I’d aim for 1.5 arc sec guiding or better. You want to keep the peaks inside that image scale as well. People with bigger scopes have much smaller imaging scales, and we must guide even better.

Focusing your guide scope is pretty simple. Get it somewhat close, i.e. round stars. Use PHD to grab a guide star, but do not guide on it. Rack your focuser slowly and watch the HFD number. You want it to be as low as you can go. Once you’ve found the lowest point, you’re golden. The basis on being ‘out of focus’ is because PHD uses a centroid algorithm to guide on the star. Personally, I do not agree with that consensus, but as an OAG user, there will always be some focus shifting when switching filters, which means that guide star will change size often.



I hope most of these will make sense for you, as ASIAir kinda dumbs things down, takes away some ability to tweak things. Theres tons of folks using them, but let me tell you, you’re better off with a nice inexpensive miniPC mounted on top, and using windows RDP to log into it.

Thank you Brian for the advice. This was super useful!!!

I was concerned that by having it with such a high frame rate, that the mount may not be designed to make adjustments at that rate of corrections.

Maybe a few years ago I would have gone with my own mini PC and a laptop. But just don’t have the bandwidth — I really would like to know what’s going on under the hood and the ASIAIR makes it difficult. Especially since documentation of what is an actually being shown is thin at best. Regarding guiding numbers, those are in arc min/arc sec. But the “size” is not clear to me if it’s pixels or arc sec. And if it’s FWHM.

But I want to thank you again for not being roosters (but in French) like people on CN. I had the worst interaction on CN when I posted this in the Beginner AP Forum.

BTW this was the result https://app.astrobin.com/i/e7ua1d

(I need to get a better image uploaded but it’s not terrible)

Quinn Groessl · Nov 9, 2025 at 08:00 PM

I probably wouldn’t dither as often. I dither once every 5ish frames for 5 minute exposures. Once every 10ish frames for shorter than that. That’s still more often than many people.

I believe that they recommend dithering in only RA for that mount because it is known to usually have a decent bit of backlash in the declination axis. And if it’s not that, the. It’s people mixing up the GTI and the non-GTI.

What are the drawbacks of dithering too often? I imagine it’s that you probably can lose a non-insignificant amount of time over the span of the night waiting for the mount to settle after dithering.

Lemme ask you a follow up question, would you answer it differently for a dedicated AstroCam vs. DSLR or just in general? I’d imagine the walking noise on a DSLR greater than with a cooled dedicated astrocam. I certainly would like to decrease my dither frequency. Gonna give your settings a try (if we have clear skies this month).

TY