Incoming duff question... camera focus

[aprecelton]

Hi everybody!

New here (can you tell)! I have a question that may need to be answered by someone with more knowledge on the matter than I have.

I am new to astronomy/photography. I have a Celestron Nextar 127SLT, to which I can attach my DSLR (pentax k100). So far so good. I can find DSO's etc that I use a number of different eyepieces to view and enjoy, but when I remove the eyepiece and fit the camera on via the t-piece, the object in question is out of focus.

Is this the way of things, that I have to then re-focus the telescope to get the image in focus for the camera? And if so, how can I be sure that the object is focused correctly 'cos the darn thing is so dim thru the camera, I cannot tell until after the exposure.

I would be grateful for any suggestions/guidance from anybody.

Cheers,

Adam

[Cornelius Varley]

Try focussing on something brighter first and then slew the telescope back to the target. You make also want to buy or make a bahtinhov mask to aid your focussing.

Peter

[Capricorn]

That is the way of things, the eyepiece and the camera are held at different positions so refocusing is necessary.

You can get a Bahtinhov mask - you find a bright star, then adjust focus to get the resultant image from the mask symetrical, then it is focused.

Problem is that unless the bright star is what you want to image then you then have to relocate the object with using your eye to do so.

Would be worthwhile accuratly aligning the scope and the finder, then focus the camera using the mask and a bright star and locate the object via the finder.

[JamesF]

What may help is if you can find an eyepiece that has a focus point close to that of the camera so that you can get it roughly right first. At least then you've got some idea where you're going. If you got the scope and camera focused on a distant object during the day and then found an eyepiece to suit that might work sufficiently well to get you close. After that it's as everyone else has said, I'm afraid. The only other solution I can think of is to throw money at the problem and buy a Canon EOS with live view

James

[Breakintheclouds]

To add to James's good suggestion, it's just possible you'll find that even if you don't have an eyepiece close to your camera' focus, you might be able to get this same effect when one of your eyepieces is, say, three-quarters of the way into its holder. If so, you might be able to make a mark on the eyepiece body so you can pop it back into the same place in the future.

[BuzzBomb]

You could get a parfocal ring for the EP? Astroboot often have them.

I use one on an old EP with Tal crosshairs to get close for webcam imaging.

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[JamesF]

And another alternative would be a flip-mirror. You'd need to get the camera to focus and then work on the eyepiece to get it in focus at the same point, but it might help. Parfocal rings are definitely useful, as are short extension tubes.

James

[BuzzBomb]

You can never have enough of either.

Well, maybe one of each would do

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[aprecelton]

WOW

Thank you all so much for your advice!

Will definately try to get a mask and see if that helps. Will also look into parfocal rings.

Having said all of that, might get a new toy in the shape of a canon EOS!

Thank you all once again

Adam