Consider my C14 at F7.7 using the ASI2600 MM PRO on a 1x1 bin. This has an effective resolution (probably never achievable on Earth) of 0.28 arc secs per pixel, so vastly over sampled.
I'm currently guiding at 0.88 arc secs per pixel through the ONAG using the ASI174 mini which is the same focal length of the main optics on a 2x2 bin.
There is no doubt about the need to bin however would you be binning 2 or 3- 4 might be a bit limiting if a spate of superb seeing suddenly hit but even a 4 bin would only be putting the optics at a theoretical 1.12 arc secs per pixel which would need superb UK seeing conditions.
It is quite a hard choice to get things right- I'm tempted to think x3 with potential drizzling. This would put my guiding and main image scale around the same.
Let me know your thoughts & I can do some tests.
It is attractive to bin, better guiding results and SNR along with smaller file sizes.
I wish you all good seeing at the theoretical limit of your optics (when you get to the moon).
Oversampled, no way. Bin, why? You want a decent image do you not? Drizzling when you have the native resolution is not the best idea. Subframe to keep down the file size if need be. BXT works better when oversampled, I and many believe. Take some test shots, these old myths will be dispelled.
Your RMS error as I'm sure you know = sqrt(seeing²+ guiding_error² + stack_error²). While seeing is dominant, BlueXTerminator - which I assume you have - can deconvolve a fair amount of it. You likely can get down to 1.2 arc seconds per pixel or even better. The defraction limit of your scope is likely under a third of this value, so you want to use the full power of your optics right! I'm at around 1.02 arc/px after BXT. 0.88 arc seconds per pixel guiding error isn't great, but not unusual. Try going unguided and take short exposures like 5 to 15s for the brighter targets, there are a lot of them. Take 5s for stars, you generally do not need a longer exposure. On many of the brighter narrowband targets, 12 - 15s Ha and Oiii works really well.
Here are some links to example images taken on a 16" F8, at the same resolution as your setup, 0.238 arc/px. Binning would have lost noticeable resolution. A compromise is perhaps to bin 2 the colour info, and bin 1 the luminance. UK skies mean you got to get stuff in a hurry so LRGB is not a bad way to go. You have 4x the light gathering power in the L. The detail, as you know is also in the L.
https://www.astrobin.com/d1ci91/C/
https://www.astrobin.com/qpe1cz/
https://www.astrobin.com/b6o690/
The proof is in the pudding!
Edited by Higgsfield, 24 June 2025 - 10:00 AM.