Imaging focus help with a PST

[Leebert]

Hi all,

I had a go at imaging with both the SPC900 and a DSLR with the PST and am really struggling to achieve a fine, sharp focus.

The webcam is through a barlow and the DSLR is 'a focally'. With both methods, I can go from blurred, into focus and back out the other side into blurred again but, looking at the screen, I can't really tell when the focus is at it's best. I end up adjusting the focus from blurred to blurred and then leaving it somewhere in the middle.

Are there any handy tips for getting spot on focus for imaging please?

Sample pictures...

Prominences by MrLeebert, on Flickr

http://farm8.staticflickr.com/7186/6949502553_95f02444ba.jpg' alt='6949502553_95f02444ba.jpg'>

The Sun by MrLeebert, on Flickr

[JB80]

This is something I struggle with too, what looks like the best focus possible on screen never actually is. I haven't cracked it yet.

With the DSLR are you using it through a laptop or using the cameras live view?

[Photosbykev]

With the webcam you could ramp up the contrast/gamma setting just for focussing, this gives you a sharper definition between light and dark. With the DSLR either use a live view x10 on the back of the camera or, for the best focus, use a magnified view on a laptop.

Even correctly focussed might look slightly soft because of the atmospheric disturbance which is where post processing of the images comes to the rescue

[Leebert]

Thanks for the tips.

On the DSLR, I use live view zoomed in (with a big jacket over my head which must look a bit odd at best!).

For the webcam, I wind up the exposure level to make it as bright as possible but will try the gamma/contrast method as soon as the sun makes an appearance.

Even with both of these methods, I can't seem to visually find the peak of focus.

I was thinking of getting a standard 52mm camera lens cap and drilling a couple of holes in it as a Hartmann Mask. No idea if that would work on a large light source though. Has anyone tried it?

[JB80]

Thanks for the tips.

On the DSLR, I use live view zoomed in (with a big jacket over my head which must look a bit odd at best!).

I've done that too, it gets hot under there.

If you can download or use the capture software that came with the camera it makes it a lot easier to see when it's on the laptop screen as opposed to the live view on the camera. It may improve things for you.

APT works good for Canons.

www.astroplace.net - APT - Introduction

You can try the demo first, it's a good little program.

[hunterknox]

If you can see the chromosphere as a separate layer at the limb then you're there or there abouts. The best tip I got on focusing a PST was someone on here (sadly I forget who) who suggested using a clothes peg on the focusing dial to get finer control.

I tried a Hartmann mask with large holes (didn't work) but might have another go with smaller ones.

Good luck!

[Leebert]

If you can see the chromosphere as a separate layer at the limb then you're there or there abouts. The best tip I got on focusing a PST was someone on here (sadly I forget who) who suggested using a clothes peg on the focusing dial to get finer control.

I tried a Hartmann mask with large holes (didn't work) but might have another go with smaller ones.

Good luck!

Thanks for the tip re the clothes peg.

What size holes did you originally use? I was considering around 6 to 10 mm holes but wasn't really sure.

Thanks

[hunterknox]

Probably about an inch if I remember correctly. Way too much. 6mm sounds good. Let me know how you get on.

[Leebert]

Thanks - I just need to pick up a spare lens cap and will try starting with 6mm holes.

I'll post back here and let you know how I get on.