Focusing the PST

[baggywrinkle]

Just looking for some tips and advice.

I am having some real difficulty focusing my PST when using either a Canon 650D or my Olympus  micro 4/3rds both of which have live view.

I have been using the limb at about x5 magnification on the viewer, but still no sharp focus. Should I use an available sunspot instead?

I am also trying to work out what exposure allows the disc and any prominences to be seen equaly well. Befiore I attach the camera I check that the etalon tuning with an eyepiece shows the prominences to their best.

[michael.h.f.wilkinson]

I hear reaching focus without a Barlow can be a problem on many PSTs. Are you using a Barlow?

[JB80]

Focus with a dslr can be really tricky, a sunspot would be a good way to get the best focus you can.

Problem with the dslr is you are getting the Green and Blue channels as well as the Red and they do interfere with the overall picture as you only want the Red channel. I'd try to get the best focus you can and then take the pic to some editing software and isolate the R channel and see if that improves the image.

For disc and proms I always used two different exposures, the proms were always over exposed.

[baggywrinkle]

I hear reaching focus without a Barlow can be a problem on many PSTs. Are you using a Barlow?

No I am not but I will try..

My Canon is a modified one , so shouldnt that help?

[JamesF]

It's quite possible that the camera won't reach focus at all without a barlow.  The focal plane isn't far enough back to reach the camera sensor with many cameras.  You might find it easier to reach focus (without a barlow) with the Neximage 5 and it might well be big enough to capture the entire disk in one go.

James

[JamesF]

Oh, and I don't see that using a modded camera would provide any significant advantage.  The Ha band is in the visible spectrum, so a standard camera should pick it up.

James

[JB80]

I would say if you think you are close to fine focus then you probably don't need a barlow.

The Ha band is really only picked up in the Red channel though so you need to separate it as the other two will muddy the image so what looks like bad focus might just be interference.

Kev has a good write up on his website here http://www.photosbykev.com/wordpress/photography/pst-solar-imaging/

Are you using your Baader Zoom? That is how I used to do it and I think how Kev did it, focus shouldn't be an issue just the fiddly fine focus is tricky.

[pmlogg]

I also had a terrible time trying to get a good focus with my PST using a 450D.  Eventually I gave up and bought a DMK41 - results were much better; even single-frame.

[Gazabone]

Thanks for the Barlow hint. I can get some shots with my Orion solar system camera but they aren't very good. My Canon is an Eos 1DX so the full frame sensor migh cause me problems......

[David Smith]

Getting to an exposure that will capture both surface and prom detail via a DSLR is very tricky. I did play around with imaging through the PST with my 1100D and a 2x barlow for a while before I got my QHY mono cam. I never found an exposure setting that achieved this, I always ended up doing two different exposures and then layering them (usually very badly in my case )

Example of layered image with 2 seperate frames taken for proms and surface

20140421Ha by David Smith, on Flickr

[Pete Presland]

I also have never had much luck using my DSLR with the PST.

[Merlin66]

Guys,

You must appreciate that the PST was designed by Coronado as a visual instrument. It was never intended as an imaging system.

This is why the back focus is marginal for almost everything other than webcams.

The 55mm backfocus requirement of the DSLR is impossible to accommodate without either serious mods to the eyepiece holder/ black box or the introduction of a relay lens/ barlow.

Such is life.

[baggywrinkle]

Thanks everyone, much food for thought.....and more bits to buy.