Imaging through a Goto Scope

Hi everyone.
When it comes to imaging Im very very new to it but can anyone advise. I have an ATIK 16ic ccd and a Celestron CPC925. For exposures <300seconds can I simply plug the camera into the rear of the scope and let it track once the target has been located. The camera weighs 12ozs.
By the same token can I expect reasonable results in whole sky imaging with a DSLR piggy-backed onto CPC.
Or do I have to "fork" out for a wedge and an ED 80 for deep sky imaging.
Silly question I know.

Silly question I know.

The only silly question is the one you dont ask!!

John, by and large what you suggest is ok. However a couple of things you need to keep in mind.

Firstly no scope will track perfectly for 300 secs or anything like it. Really any exposures over 30 seconds will require a means of guiding the telescope. Autoguiding is the best way to do this, however you should gain more experience using much shorter exposures (moon planets etc) before going down that road.

Any Alt-Azimuth mounted scope such as the CPC will exhibit 'field rotatation after a certain length of exposure. This will show up as an apparent rotation of the stars around the centre point of the image. The only way to permanently get rid of this is by using a wedge, and even that has issues with wind and stability.

The good news is that you can get over both of the above (to a degree) by taking manay short exposures and stacking them together using something like the free 'Deep Sky Stacker' software. Try taking 50 x 30 second images, manually remove the ones with star trailing and stack the rest. You'd be amazed at what you can do this way.


Using a DSLR piggybacked is a great way to start, you still suffer from the above two problems, but to a lesser degree because the lens has much lower magnifaction than the scope and doesn't exhibit the symptoms so fast.

Hope some of this helps.

Dave, will periodic error show up in 30 sec exposures, or any exposures as a sudden movment of the mount, or is it periodic error that prevents perfect tracking for longer than 30 secs and causes a gentle degredation of the tracking like you mentioned previous?

Fintan,

Most scopes should be capable of tracking for 30 seconds, with a reasonable alignment done. Periodic error should not be a problem since periodic error only reaches its maximum after one complete revolution of the RA worm. In an Alt-Az scope periodic error can be present in both axes but by the nature of how an alt-az scope moves, can be less of a problem.

Periodic error shows up as a gentle tracking error. Sudden movements may be realted to wind, electrical problems or grit/grime inside the drive train (or maybe the scope being bumped by your mutt:)

Dave
Many thanks for your reply. Have DeepSky Stacker downloaded I have registax already. So I will try for shorter exposures say at 30secs. So how many on average would you think for reasonable Mars images.
How do you rate the Atik 16 anyway?
General pice of info. Sky at Night magazine has gorgeous screensavers on the cd.
Anyway thanks for info and will try it next clear night if there is to be one in our lifetime!!!!!
Have a good one

John,

The ATIK16IC is really a deep sky camera. For planets I suggest using a webcan which can capture thousands of images in a video file which can them be processed by registax.

For deep sky imaging with the ATIK 16IC, I suggest that you get as many images as the conditions allow, remember you will lose some to tracking inaccuracies so take more than you think you will need.

I often put over 6 hours of exposures. You might consider that excessive, but its not. Using shuch short exposurtes you will really need at least 100 to get anything really decent.