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Bert,
It is never a waste of time accurately focussing your system !
Using FocusMax will take about 60 seconds and nail it every time and do it automatically. No human error.
At least do it all once so the focus offsets are accurately quantified and recorded in your software and then focus the first filter so you have an accurate relative starting position each night.
A night of bad focus will ruin the whole night, a season of relying on unreliable information could potentially ruin a season.
At least in terms of capturing the best FWHM that could have otherwise captured - meaning much better nebulosity detail, you would want to use a quantifiable focussing methodology.
You spent a small fortune getting a wonderful OTA and an electronic focus system that can focus your stars to a tight point and then to rely on a Bhatinov mask and leave it up to the gods that nothing will change throughout the night !
The CFZ on the RH200 is about 21 microns (in the blue) I think for your OTA, so you have a system that is quite sensitive to focus.
According to your figures, the focus position varies from 68µm to -34µm although at least LRGB is almost parfocal to within 17µm.
So this will be a much greater problem for narrowband than LRGB
So that is a maximum range of around 100µm with a system that only has a focus range of round 20ishµm.
That indicates to me that Focus is likely to be the weak link in your imaging systems fine tuning.
Given the CCD has 9µm photosites and the OTA can focus to 8µm (central area) any variation in focus is going to bloat your stars.
So I wouldn't discount the necessity to focus no matter how little time it might take - which just isnt much if you are using Focusmax
Just my 2c worth for what its worth.
Rally
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