Noob Questions about SCTs and Astroimaging witha DSLR

[Zaphod_B]

Hello all,

Apologies in advance for the noob-ish questions.

Just starting to get into astro-imaging with my Canon 400D DSLR. I have a Celestron NexStar 6SE telescope with a 2" Meade diagonal.

My first test shot, taken this afternoon of a church spire on the horizon, was rather disappointing, - OK it is rather hazy but nevertheless, disappointing.

I have put Celestron's 1 1/4" T-adapter into the EP hole of the 2" Meade diagonal, fitted the T-ring to my camera, focussed the image using the focus knob on the 6SE and, with the camera set to "auto", pressed the button. The image is OK, but hazy.

Am I correct in thinking that instead of using the 2" diagonal, I should couple the camera to the back of the telescope buy using an SCT to T Mount adapter?

Am I also correct in thinking that this is prime focus imaging?

Is there any way of adding an eyepiece to increase the magnification? The Celestron 1 1/4" adapter seems to be able to accept some sort of accessory as there is a knurled screw sticking out of the side,

How do you add an EP to the setup.

Also, where would you put a filter, such as a Moon filter? I know these screw into the end of the EP's - but where do they go if you aren't using an EP?

(Writing this at work at the moment - so not able to look directly at the bits & bobs. Some of the answers to the above may become self-evident when I have a closer look at the adapters).

Thanks in advance

Zaphod

[Merlin66]

Here we go.....

Don't use the diagonal, use as you rightly suggest a SCT to T thread adaptor

This will give you prime focus imaging.

If you really want to increase the magnification ( why!??) there's a couple of ways of doing it.

You can use a Barlow lens, x2, x3 etc and then put the 1.25"-T2 adaptor in the end of the barlow tube.

or, you can buy a cheap "eyepiece projection adaptor" which lets you put your favorite eyepiece inside a "tube" which then allows it to act as a ----- projection lens. By varying the distance from the eyepiece to the camera, usually with spacers, you can change the magnification ratio ie x4, x5 etc.

The filters can either screw onto the SCT thread, or (hopefully) onto the end of the Barlow or the eyepiece.

Hope this helps

[Psychobilly]

other things to think abotu are mirror lockup on the DSLr... as when the mirror flips this will cause vibration ... mirror lockup puts a delay betweent he mirror raising iand the exposure being taken... and how did you release the shutter either use a cable release, do it remotely from the computer usign the EOS utils or use the self timer...

Billly...

[Zaphod_B]

Thanks Merlin:

This is just what I suspected, but I thought that I'd check first.

I'm not sure what you meant by your question about increasing the magnification however. If you put your camera onto the scope via the T-mount/T-adapter, don't you just get a single magnification?

Psychobilly:

Thanks for your input too. I'm planning to activate the shutter via the IR remote (or via the self-timer). I can't remember offhand if the 400D has mirror lock-up (I suspect that it possibly has) and if so, after centering the object, I'd use that to minimise vibrations.

Looking to update with a webcam of some description at some stage and any advice on a CHEAP but DECENT webcam would be appreciated.

Thanks for the replies guys.

One question about prime focus imaging. Where would you place a 1 1/4" filter (such as a Moon filter) if using the SCT to T-mount adapter and T-mount on the camera?

Zaph

[Psychobilly]

Mirror lockup will be buried in the custom functions menu...

Philips SPC900 or the older Toucam II Pro (840K) are useful webcams with loads of info on moding them for long exposure etc.

1.25" filters will almost inevitably lead to vignetting with APS-C sized sensors... although steppenwolf has come up with a novel solution...

Billy...

[Merlin66]

A barlow infront of the T adaptor will change the magnification.

Fitting the filter is a little more problematic!

[Zaphod_B]

Mirror lockup will be buried in the custom functions menu...

Philips SPC900 or the older Toucam II Pro (840K) are useful webcams with loads of info on moding them for long exposure etc.

1.25" filters will almost inevitably lead to vignetting with APS-C sized sensors... although steppenwolf has come up with a novel solution...

Billy...

Hi Billy

Yes, now you come to mention it, I think it is (just dashes off to check). Yes, it is CF #7 - set to 1 for Mirror Lock Up (two presses of shutter button to take photograph. 1st press moves mirror, 2nd press opens the shutter - or you could use the self-timer in which case setting the timer locks the mirror up).

Zaph

[Psychobilly]

Yes mirror lockup can be linked to the self ... A single shutter press locks up the mirror then takes the shot after the self timer delay.

Billy...

[Zaphod_B]

Thanks for the reminder Billy

Zaph