focusing/magnification

[musherrob]

Hi All...Have just taken a few tentative steps into imaging.I am using a Tal 2m and Canon eos 300d and trying to acheive prime focus my starting point will be the moon.The problem is it is difficult to see thro the viewfinder if focus has been reached.I appear to get the sweet spot but when the sample images are downloaded they are not crisp.The settings are iso 200 and manual/bulb mode.I use a shutter release cable.Would the Auto mode be a more accurate considering the Mag of the Moon.?In the focal plane i have fitted a LP Filter.

Because of the focal length of the Scope are there limitations ?My ideal conception is to be able to magnify the image somehow under the present set-up and then focus in on that.Anyhelp appreciated !! Ta Rob

[tooth_dr]

Are you attaching the 300d directly to the scope? If so I find it's best to get close to focus via the view finder on the camera, then zoom in on the LCD using the buttons on the back of the camera, and check focus. Next turn focuser on scope slightly and take another image and zoom in again. Repeat until focus is 100%, if you go past the sweet spot the image will become out of focus again. I often focus on a bright star as it's easier to see if the focus is right. DSLR focusing with a scope is a widely covered area, and some methods suit better than others. Have a search around the site for threads covering this topic.

You can alter the settings in manual mode until the Moon exposure is correct, I wouldn't bother with auto modes imo.

[musherrob]

Hi and thanks for reply,The camera is attahed to the focussing tube via a M 42 adaptor.Not certain if i am able to view thro the LCD as i think this model does'nt have the Live View facility.Correct me if i am wrong.Thanks Rob

[tooth_dr]

It doesn't have liveview, I use the same camera! What I mean is that once you've taken the image, review it on the camera LCD screen at max magnification (press the + button). If the focus is not really tight the stars will be much larger than the 'dot' that appears at the bottom of the screen inside the small box. Adjust focus slightly in one direction, then take another exposure. Zoom in again on the camera LCD review, and this time use the wheel on top to flick back (left) to the previous image. This will keep the image magnified as you flick back to the previous image, and allow you to assess whether the focus has been adjusted the correct way. Repeat until star is as small as possible. I hope that is clearer.

It takes time and patience, but I find good focus quickly, you just get a feel for it.

Hope that helps!

Adam

[mint_mark]

Hi and thanks for reply,The camera is attahed to the focussing tube via a M 42 adaptor.Not certain if i am able to view thro the LCD as i think this model does'nt have the Live View facility.Correct me if i am wrong.Thanks Rob

If you can attach the camera as though it were an eyepiece (using a 2" or 1.25" adapter), then you can use a Barlow lens between the camera and scope to increase your magnification. The amount of magnification you get depends on the distance between the Barlow lens and the camera's sensor... a 2x Barlow will probably give near 3x magnification with a DSLR. That's what I found anyway.

I sympathise with focussing issues... my telescope has a focus locking screw, but when I tighten it the focus moves unless I am very gentle.