My comments here are certainly my own and it should be said that I am no expert by any means. My path to better guiding is based on both my successful outings and my less than optimal sessions. What I have experienced in the way of achieving sub arc sec guiding consistently throughout the night is opposite of what I read and hear from social media. Trying to guide with half sec exposures and increasing the aggression (and other guide related settings) have not provided good results for me. The opposite has proven successful and I think I know why. When atmospheric turbulence is high or transitions high during a session the perceived movement of the stars will send a guide pulse to the mount in conjunction with the exposure length you select. If that exposure is to short you are “chasing the seeing”. I found 2-4 seconds allows the software to average out the perceived motion and send one corrective pulse verses many incorrect ones. All of this is of course my findings and during times where conditions warrant adjustments. Sometimes you just guide all night at ½ arc seconds and all is well. I trend towards not however.
Better guiding through trial and error
Steven Rengers · Dec 23, 2025, 07:26 PM
“chasing the scene”
I think it’s chasing the seeing ;) Anyway, I’ve had great experience with 1-1.5 second guiding exposures myself with the 150i.
Another thing I personally do that most everybody would say is wrong, is I calibrate at my target. I don’t worry about doing it at the celestial equator near the meridian.
The guidance I have seen for strain wave mounts is that they must be corrected more frequently than conventional mounts, hence exposure times of 1-1.5 seconds. I’ve had good results using 1-second exposures with my Wave 150i, but I do not adjust any other parameters specifically for the mount (aside from the recommendations that come from the Guiding Assistant). I have gotten guiding as good as 0.3” but typically I’m between 0.5” and 1.0”.
I confess I don’t think I’ve tried guiding with this mount using exposures longer than 1.5”. Maybe I’ll try 3” just to see what happens.
Steven Rengers · Dec 23, 2025, 07:26 PM
Trying to guide with half sec exposures and increasing the aggression (and other guide related settings) have not provided good results for me
What does that mean? Worse FWHM and eccentricity of the stars in your sub exposures? Or just a nicer guide graph?
Many people concentrate too much of what the guide graph says. What only matters are your sub exposures. I would be surprised, if longer guide exposures would work for your strain wave mount as almost all of them come with greater amounts of periodic error. But your local seeing may mask underlying tracking errors, too.
Steven Rengers · Dec 23, 2025, 07:26 PM
If that exposure is to short you are “chasing the seeing”
Should not matter too much with todays guide programs and multi star guiding. Unless you are using an OAG and can only find 1-3 guide stars.
Steven Rengers · Dec 23, 2025, 07:26 PM
“chasing the seeing”
For example, I guide videobased with 50-80 frames per second on one star and get a total rms during the night of 0.2-0.4”. The only time my guiding struggles with “chasing the seeing” is when the seeing is so bad, that imaging that night is not worth it at all (3-4” star FWHM).
My point was to say that my seeing sometimes (not always) gets worse during the course of my session. My previous tendency has been to shorten the exposure. Now I find longer exposures work better assuming the issue of bad seeing is determined after all the other variables have been eliminated.
I have used Chatgpt to analyse the PHD2 log file, it then produces a recommendation for the guide settings, after a few sessions you get to understand what settings to change for yourself, my guiding is now regularly hovering just under 1 arc second.
I went through similar preponderances until…. Until I stopped moving my scope from night to night. I realize some/many can’t do that. But if you can set up in your own backyard, cover your scope in place, then come back to it the following night/nights you will see improvements in your guiding. I did.
So much so, I don’t move my mount so it maintains its polar alignment very well, and ASTAP can set it on the object for the night easily.
It’s all a part of the learning curve, soon you’ll get your guiding as low as it will go. Then, the seeing will drive you nuts because it varies a lot and affects your guiding without anything apparent.
But, for me, the less my mount was moved the better things got for me. Over the years I settled on a good spot in my backyard, and I keep things as stable as I can. (Even in spite of covering and uncovering every session.)
I won’t tell you my guiding. No need to hurt your feelings.
What are you using to Polar Align? I use Sharp Cap and have for years. it is worth the buy in to me just for its Polar Align scheme. But once I was really curious, so I did many, many polar alignments one night. Every one asked for adjustments each time even though nothing had moved or been changed from the previous half a dozen routines. 😖 I believe what was going on was variations in the seeing, or atmospheric changes.
What matters the most is not the figures, while they do give you reference. What you get for your results is more important. Just try and do your best each time and the results will improve eventually.
Don’t tear your hair out. 😉
I use PHD2 and started with PHD1 a long time ago.
Once you are plopped down for the night, do your Polar Align, build your model (alignment), and try some bright stars to see how your mounts guiding is. Another thing I do is to build my modeling with many stars. I like to do 10 East, then 10 West. The more the merrier. Because each alignment star helps your mount zero in on the sky. The more you put into it, the more you’ll get out of it. If you do 1, or 3, you won’t be as apt to land on your objects as if you train your mount more.
This is supposed to be fun, not taxing.
Well no hair left to pull out so that’s a win. I agree with everything all of you said. I do worry about the roundness/elongation of the stars in the subs first and foremost. But so far bad guiding usually goes hand in hand with bad stars to a degree. I realize bad seeing combined with bad guiding does not always mean your subs are bad. I guess I am just particular about the guiding numbers. Perhaps I will learn to get over that!
Steven Rengers · Dec 23, 2025, 11:29 PM
Well no hair left to pull out so that’s a win. I agree with everything all of you said. I do worry about the roundness/elongation of the stars in the subs first and foremost. But so far bad guiding usually goes hand in hand with bad stars to a degree. I realize bad seeing combined with bad guiding does not always mean your subs are bad. I guess I am just particular about the guiding numbers. Perhaps I will learn to get over that!
I think you are probably like most here, trying to do your best.
Just don’t forget to have fun while trying.
I couldn’t tell you how many nights I flat gave up. Even still do have the occasional still. I bet we all do.
I have always used 1 second exposures for my guiding. Just a nice round number, not too short, and not too long. I like to set it and forget it as much as possible.
Wear a hat to keep your head warm. 🫡
Hi,
I can share my experience from the last four years. During that time I used several mounts, ranging from an EQ5 up to a 10Micron 2000 QCI. In between I ran two EQ6-R Pros, an EQ8, an EQ8-R Pro, and briefly tested an RST300 borrowed from a colleague.
I experimented a lot, read extensively, and spent quite some time optimizing settings to get the best possible performance. What I eventually found is that the key factor is not so much the atmosphere itself, but the image scale you are working at, meaning arcseconds per pixel.
If you want consistently round stars and to extract the maximum detail, I find it works best to keep guiding accuracy within roughly 50% of your image scale. If you want some margin, even 30–40% is a good target. In my opinion, the mount type is less important than how well it is configured and operated.
This is where turbulence comes into play. As you mentioned, mounts can end up guiding the seeing, which hurts the final result. The way to avoid this is by using the right PHD2 algorithms and carefully tuning aggressiveness and min-move.
As an example, with an image scale of about 1.5 arcsec/pixel, I guide in RA using Hysteresis with roughly 60% aggressiveness, depending on how the mount reacts. Min-move in RA is set around 0.28–0.30 pixels, which means the mount only reacts to real errors, not seeing noise. A min-move of 0.5 pixels would already correspond to about 0.75 arcsec, while 0.3 pixels keeps corrections closer to ~0.45–0.5 arcsec.
In theory, such small deviations are seeing-limited anyway, but in practice too many corrections tend to wash out fine detail. The goal is therefore to generate as few guide pulses as possible while staying below roughly half of the pixel scale.
Regarding guide exposure time, my rule of thumb is: the better your polar alignment, the longer you can expose. Longer exposures calm the guiding and average out seeing, while still reacting to real mount errors rather than atmospheric noise.
My current setup:
150 Quattro at 518 mm focal length on an EQ6-R Pro, guiding via OAG with an ASI220MM (4 µm pixels). Image scale is about 1.5 arcsec/pixel.
PHD2 settings:
RA: Hysteresis
DEC: Lowpass 2
RA: Aggressiveness 60%, Min-Move 0.28
DEC: Aggressiveness 80%, Min-Move 0.35
With this configuration I typically see a total RMS between 0.35 and 0.55 arcseconds, mainly driven by wind rather than seeing.
CS Nedim
Nedim Bevrnja · Dec 24, 2025, 11:29 PM
Hi,
I can share my experience from the last four years. During that time I used several mounts, ranging from an EQ5 up to a 10Micron 2000 QCI. In between I ran two EQ6-R Pros, an EQ8, an EQ8-R Pro, and briefly tested an RST300 borrowed from a colleague.
I experimented a lot, read extensively, and spent quite some time optimizing settings to get the best possible performance. What I eventually found is that the key factor is not so much the atmosphere itself, but the image scale you are working at, meaning arcseconds per pixel.
If you want consistently round stars and to extract the maximum detail, I find it works best to keep guiding accuracy within roughly 50% of your image scale. If you want some margin, even 30–40% is a good target.
At 0.33”/px, I don’t think I’d see guiding at 50% of that even if I had 1” seeing, let alone 2.7” at very best…. Maybe because I’m so oversampled, but I find keeping total RMS below a third of the seeing at the time is sufficient. Also, I can have terrible total RMS and round stars, and low RMS and oblong stars; if RA and DEC are roughly equal, stars may be bloated but round, and the more RA and DEC differ, the more misshapen the stars, even if small.
Cheers,
Scott
Thank you all for sharing your collective experience’s and personal settings and tweaks. It’s so beneficial to see what experienced users do to achieve the amazing results we see posted here on Astrobin.
With my AM5, I always change settings according to atmosphere which -I think- affect the guiding the most.
In PHD2, 1 second is my sweet exp, always calibrate at celestial equator, Ra & Dec. Agg. is between 40-60%, and PA with Sharp Cap. most of the sessions I got RMS 0.5-1
Sometimes when I see the bad atmosphere I know I will get high RMS and it happens !
Cables arrangement is sometimes I missed.
Imaging scale is what decide RMS is ok or not, so don’t stick with numbers range too much.
I used to ruthlessly chase low RMS numbers but these days I really don’t pay much attention to it. I just calibrate as close to 0 dec. as my site allows and don’t re-do it unless the guide camera has rotated. After a cal. I run the guiding assistant and accept the recommendations. I used to use predictive PEC on RA but I think that caused more problems then it solved so I just use hysteresis in RA and resist switch for DEC. The only other change was camera gain to make up for my rather bright, B8 sky. My guide exposures at 2.5 sec. That’s with an EQ6r-pro mount. Oh, and I do use a 25A red or IR pass filter.
For my rig, wind seems to be the major enemy. I shoot at 900mm and 1800mm at 0.66 and 0.33 arc/sec per pixel. I get round stars after culling out the few subs that exceed my eccentricity limits. The bottom line is I don’t sweat the numbers but rather, just let FWHM and eccentricity be my guide. Averaging is a wonderful thing!