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I also use an Atlas focuser on my Riccardi Honders.
Its quite easy to use and is very precise. At present I am not using Focusmax or other software but about to implement one.
One thing that does concern me about automated focusing is the fact that all electronic focusers I have used including the Atlas (the most precise) seem to focus best moving out towards the focus point rather than in.
So you manually focus, you get a spike in the sharpness graph (I use CCDsoft at the moment and about to stop using that as well in favour of Sky X). Then if you go past it its not a matter of reversing the same number of steps. It will be further away. I suppose this is some friction or fighting gravity.
I wonder how that impacts on V curves.
Anyway, focusing is a breeze with the Atlas and precise focus is easy to achieve and obvious. The image also looks a certain way.
Roland Christen focuses using a single star and I think probably in the centre of the image. Use subframing to get a good look at the stars and you can compare them when the new image downloads to see if they get smaller.
I would rough focus on 2x2 binning and then use 1x1 if I wanted a tad more accuracy.
This is at F3.8.
Another factor is unless your camera is perfectly square to the scope then the whole image will not come to focus at the same focus distance.
You can see the top or left or right side being sharp but the other side not as sharp. That is your camera not square or it is flexing slightly.
In that case, square up your camera and pack out the offending sides or if still a slight error a compromise focus position will be required. An automated focus routine must do some average of the image or just uses one star so it would be safest to pick one in the middle where these flexes revolve around and is really the midpoint.
Roland also focuses in such a way to allow a bit of change as the temp shifts.
How much it shifts with temperature is something you'd have to log with accurate temp info.
The Atlas has a temp sensor in it but its inside the focuser and I find its slow to respond to ambient and is always showing it as warmer than the ambient. I tried to work out how much the focus shifts with 1C and it was a bit hard. My best guess is about 50 steps out as it cools (AP RHA). That's not much.
I focus at the beginning of the session and then again after an hour or so and it usually refines a little. Luckily the RHA is pretty temp stable focus-wise but there is a change. Not like an FSQ which shifts a lot.
Focus can also be hard in bad seeing. Comparing 2 images becomes hard as one has better seeing than the other so even though you are improving focus it can look worse. So if you think you are on track to sharper focus but the next image looks worse, wait a second and take another to check.
I use Astrodon LRGB Gen 11 filters which promote they are parfocal. Its very handy. I do find that they are in fact parfocal so I focus using Luminance and that seems to be correct for RGB Ha O111 and S11. Very convenient! Baaders promoted that they were parfocal and they were way off. That was a few years ago so I don't know if they have fixed that. Also they promoted they were 1:1:1 colour combine and they were way off! Gee honesty in advertising!
Hope this helps.
As I say I am about to use FocusMax Pro so I will be posting questions soon myself! I am overdue to using it. But I am confident my manual focusing is super accurate and that's the Atlas. Its a beautiful piece of astro gear. Super expensive but amazing.
Some scopes hold their focus better than others. My CDK is all carbon fibre and it does not shift focus that much but there is a minor change with temp.
The old RCOS carbon fibre promoted focus and forget and same focus night after night and that was somewhat true. Perhaps not entirely.
Greg.
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