Two questions!

[EdF_uk]

Hello everyone,

I have been doing some research tonight about astro photography anfd have a couple of questions. I'm sure I'll find the answer when the book that I've just bought arrives - Making every photo count, but I thought I'd ask here first.

1) CMOS vs CCD. I've read somewhere that a CCD sensor is better than a CMOS sensor for a number of reasons so I naturally thought that Canon DSLRs would be CCD type, however they're not. I take it that decent CCD sesnors are much more expensive than a standard DSLR, is this correct?

2) I've seen lots of refrences to an autoguider. What is this and how is it used? Do you have to use one, as I thought a motorised mount can track?

Hope someone can enlighten me.

Many thanks

Ed

[JamesF]

1) I get the impression that a while back there was a definite difference in quality between CMOS- and CCD-based systems, but that gap seems to be closing now. A DSLR is still probably cheaper than a dedicated astro camera, though I'd not be surprised if it comes out fairly close if you have it modded, and the DLSR will probably have a far greater resolution for an astro camera in a similar price bracket. On the other hand, astro cameras are probably less "noisy" because they're cooled properly.

2) Guiding is basically a feedback system for the tracking. Tracking works by rotating the scope around the RA axis at a fixed speed, but doesn't generally allow for imperfections in the manufacture of the mount that mean the view drifts over time. If you have a second telescope pointed at a star somewhere close to the object you're imaging and camera (or an off-axis guider), it's possible for software to make small adjustments to the way the mount tracks to account for those imperfections, based on any movement of the star in the guide camera image.

James

[EdF_uk]

Thanks James.

I understand the guidescope now. Thanks

Looking forward to reading my new book when it arrives.

Many thanks

Ed