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Hi Matty
My experience with unguided long focal lengths of around 2000mm is that exposures of anything more than ¼ to ½ second will not be critically sharp due to the Earth’s rotation. Although a focal reducer will perhaps allow exposures up to maybe 1 sec without trailing, the real answer to long exposure imaging is a Polar Aligned Equatorial Mount.
Tracking in Alt-Az mode may lengthen the exposure time at the centre of the Field Of View (FOV) but other field stars will show increasing trails the further you move away from the centre.
I have an excellent German Equatorial Mount (GEM) and even when accurately polar aligned, I personally find long exposure imaging (60 secs or more) quite a challenge even when using auto guiding let alone simple tracking of the Earth’s rotation.
Anyhow, give it a go as there is nothing like practical experience to help you understand the concepts, processes and results from experimenting with what you have, before rushing out to purchase new equipment.
You should be able to see Ceres and the brighter Minor Planets on the notebook display with sub 1 second exposures. Here is an example of the effect of different length exposures using my DMK on the Trapezium. With an F12 ‘scope and an x2.5 Barlow I was working at an effective focal length of 5400mm which is around F30 for the system, albeit on a GEM whilst tracking (not guiding).
Cheers
Dennis
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