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Attaching a camera to telescope


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I am a newbie to telescopes and astrophotography.

Yesterday I bought my first scope celestron nexstar 90GT.

I am a hobbyist photographer so I own a couple of DSLR cameras.

Now I have been doing some research and I believe that I need a 1.25 T2 and also a T mount to suit my camera.

Am I correct or am I missing something?

Thanks in advanced

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Firstly, an ALT / AZ mount isn't ideal for imaging faint deep sky objects due to the field rotation of the object.

Rotation-Animation-With-Box-Small.gif

When using an EQ mount the telescope is rotated thus keeping the subject "fixed" in the field of view

Rotation-Animation-With-Box-EQ-Small.gif

However, you could always use a web cam and stick with luna and bright planets where field rotation won't be an issue due to the short exposures.

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There are two webcams that are popular - the Phillips spc880 / 9i00 and the Microsoft livecam.  The Philips is now quite hard to get hold of, and if you do find them are typically £80 ish   To use the Phillips you need nothing more than a 1.25" nose cone so you simply substitute the eyepiece for the camera.  The MS LIvecam needs a little more modification by fitting the innards into a modified case... but still easily doable 

The next phase would be to buy a dedicated planetary camera, and then a fast CCD camera that can take short exposures of faint objects, thus removing some of the field rotation issue... but these are not cheap, and you would be better off investing the cash in an EQ mount and using the correct T ring to mount the DSLR camera body to the scope.

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You are correct on what you need. You'll also need to learn how to shoot flats (have a look at the Deep Sky Stacker help) as 1.25" fittings will introduce a lot of vignetting.

As long as you can achieve a reasonable balance (by moving the tube forward) you should be able to get a start on some Deep Sky imaging. There are some inherent challenges and limitations though. You will be limited in exposure time depending on where you're aiming... 30 - 40 seconds in North-South and overheard, up to maybe 2 minutes, low in the east and west. Also, the drive accuracy may not be up to manageing many 2 minute exposures. My NexStar SLT was pretty good up to 1 minute, dropping maybe only 1 in 10 frames due to drive errors, but at 2 minutes, I was losing 50%. Shoot a very large number of frames, and see how you get on (I was able to get the bubble nebula with an unmodded dSLR). 

Good luck.

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