Deep Space Objects (imaging)

[Keithp]

This may seem like a stupid question to the more experienced dso imagers here...but I'll ask it anyway seeing as I got all the kit ready to go and just waiting for a break in the clouds and rain:mad:.

When you do a series of subs over several days/weeks etc how to you line back up with the object to take further images to add into the stack?

Do you have to start at the same time each night? So the object is in exactly the same spot when you did the previous images...

There you go I've asked it:)

Regards

All

Keithp

[brianb]

There is a certain amount of tolerance, but:

1. Align the camera the same way - I would usually have the long side of the frame running E-W which is easy to achieve either by watching the drift with the drive switched off or slewing in RA

2. Centre the same object in the frame

Stacking programs like Deep Sky Stacker will cope quite happily provided the aim is reasonable i.e. 75% of the frames are overlapping. Much less than that and you will probably have issues with image quality anyway as some pieces of the image may not have much exposure time.

[Keithp]

Cheers Brian, the other part though...would you start imaging when the object is in the same part of the sky each time, or so long as the viewing frame is complete it wouldn't matter ie the object could be in the SE, S or SW?

[roundycat]

I think it stands to reason that you will probably image in the same part of the sky as you will start as early as you can. It doesn't matter though, any time (direction) will do.

I have alignment marks on my cameras so I can align them as accurately as possible with the mount. Point the mount to the meridian and set the camera to landscape or portrait mode and take care to repeat the positioning if you have to move it. With practice you can get within 1-2 degrees.

When you have a set of subs but want to add to them, roughly combine the first lot and give a sufficient stretch to see the image, don't worry about quality. Save it as a jpeg and have it on screen for when you start a new imaging run and use focus mode to compare the new picture with the old one. I find that doing a quick re-cal on the same, close star before doing a go to will help with the accuracy. You may then only need to give it a minor tweak.

Dennis

[brianb]

.would you start imaging when the object is in the same part of the sky each time

Doesn't matter much but try to keep well away from the horizon ... distortion caused by differential refraction can be a problem at low altitudes.

[Keithp]

Many thanks for all the replies, hopefully I can get cracking this weekend.

Regards

Keithp