Multiple day exposure sessions

[SimmoW]

Since my backyard is 'tight' and may not permit more than a couple of hours' imaging sessions each day, I was wondering - how on earth do you guys & gals reposition the mount and scope in exactly the same way each night?

Yep, I don't have the luxury of a permanent Obs.

I am guessing that I'll be placing the mount tripod in close to the same orientation each night (I'll be getting some pavers to help stabilise the thing), and of course it'll be 2 or 3 star aligned.

Assuming I remember to save the actual position of imaging on my NEQ-6 mount controller, can I assume that if I just slew to the same place each day, the way the mount works on the Alt/Azimuth axes, will mean that its orientation to the horizon will be the same each time? I reckon I'd go crazy perfecting alignment otherwise!

Advice & ideas muchly appreciated.

Being only a beginner, I won't be doing very long exposures at first anyway, but I hope to be getting to 2-3hr sessions eventually, so am really curious as to what ppl do here!

Arggh, the wait to use my new Tak is killin' me. Claude is taking his time sending over the final bits and bobs so I can image. Eg. a tubeholder assists, just slightly...

Thanks

Simon

[RickS]

So long as you have a process for accurate polar alignment each time you set up the other thing you need is the ability to accurately point at the same FOV each time. The secret to that is plate solving.

A plate solver can inspect an image and compare it to a sky catalog to determine exactly where the scope was pointed when the image was taken. It may need some hints to do that (e.g. the image scale and a rough idea of RA and Dec) or it may be able to work it out without hints at all - this is called blind solving.

There are a number of plate solving software packages around. Pinpoint is a well-known commercial product and a "lite" version is bundled with MaximDL. Elbrus is a free package. The Astrometry.net solver can do blind plate solving and is also free. Astrotortilla is free package based on the Astrometry.net solver.

If you have some images from a previous night you can use plate solving to determine where you need to point your scope to collect more data on the same objects. You can also use plate solving to assist with accurate pointing by slewing to your object, taking a test image, and solving it. You may find that the scope isn't pointing exactly where you thought. Sync the mount position to the result of the plate solve and slew again. Repeat if needed...

Automation software like ACP, SGPro, CCD Autopilot and CCD Commander will do all this for you and makes multi night projects a lot easier.

Cheers,
Rick.

[SimmoW]

Thanks Rick, great explanation. Just wonderful, I'll get to Fiddle with even more software!