Focusing

[Bendeavour]

hi,

I was just wondering how do you get sharp, focused images when a camera is attached

thanks

[ronin]

Bahtinov mask and live view.

Stick mask on the front, aim at bright star, get image correct on the live view, lock the focus, take mask off, aim at the object to be imaged, do the imaging.

[sixbytes]

Without Bahtinov mask: Use live view to aim at a bright star, turn up digital zoom function to maximum and focus until star is smallest.

[JamesF]

Webcam, or DSLR?

James

[ollypenrice]

Without Bahtinov mask: Use live view to aim at a bright star, turn up digital zoom function to maximum and focus until star is smallest.

This doesn't work. It's a very rough guide at best. We can be sure of this because, when refining focus using a software tool which measures the width of the star at half its maximum brightness (FWHM) considerable reducions in measured diameter are imperceptible on the view of a zoomed-in star. Focus is absurdly critical in imaging and visual estimates simply don't get near to what is possible. The faster the focal ratio the shallower the depth of focal plane. In an F5 Newt it's shallow. In a Hyperstar it's terrifyingly shallow!! The effect of tight focus in imaging is enormous. My own routine is Bahtinov refined by FWHM. The length of sub exposure used to study the star's focus is almso important. I think around 3 seconds is optimal since it lets the vagaries of the seeing average about a bit. In 1 sec subs the star bounces around a lot and you learn very little. If you are oversampled you get a more consistent result and if undersampled a rather wild one.

A Y mask is a decent alternative to a Bahtinov and takes 2 minutes to make at almost no expense.

Olly

[Bendeavour]

by the way its a dslr and doesn't have live view unfortunately

[ndastgir]

by the way its a dslr and doesn't have live view unfortunately

try one of those DSLR video recording software. if you have a canon you can use EOS Movie Recorder.

[Bendeavour]

try one of those DSLR video recording software. if you have a canon you can use EOS Movie Recorder.

its a nikon and unfortunatly doesn't have video mode

Is my best bet trial and error on a bright star, planet or moon?

[poogle]

Buy or make yourself a Bahtinov as stated previously and take several shots until you get the focus right. Thats how I do it. Once you get a hang of it it'll only take you a couple of minutes to get it right.

If you have a laptop attached to the camera you can use http://www.digicamcontrol.com/ to control your Nikon and view the images on the screen, it'll make the process even easier.

/Patrik

[ollypenrice]

You don't need live view with a Bahtinov. Just take a pic and look at it.

Olly