Calculating best resolution of 4 inch scope

[mbushell]

I have a basic question that I should be embarassed to ask. I have begun solar imaging with an NP101is and a Solarscope 100mm hydrogen alpha filter. The question is about what kind of resolution I can expect to get. The Dawes limit on a 4 inch scope is about 1.6 arcseconds I believe. Since the sun is about half a degree that means it is about 1126 Dawes limits wide. Does that mean that there is no purpose in trying to produce an image of the sun that is more than 1126 pixels in diameter (whether it is done by varying camera pixel size or scope focal length)? I have certainly seen images out there produced with a 4 inch scope that have better resolution than this. So I am probably grossly oversimplifying this or calculating from ignorance. Thanks in advance.

[hunterknox]

Firstly, what a fantastic setup!

He's mostly on another forum these days but fortunately markt's got you covered: http://brierleyhillsolar.blogspot.co.uk/2013/01/nyquist-sampling-theory-undersampling.html?m=1

[mbushell]

Thanks hunterknox. What a fantastic article. It appears that for my setup (NP101is/Solarscope 100/PointGrey 3.45 micron camera) the ideal is 1051 mm. That is almost exactly double the native folcal length so a 2x Barlow should do the trick. I have tried that and got nice images, with dark and light bands. When I can deal with those I should be able to make some nice pics!

Is it possible to post pcs here? They inser OK in the message but I get a posting error (oddly it says the post is too small).

Thanks for the link. It was a big help!

Mike

[JamesF]

I did similar calculations some time back for planetary imaging, but the first section applies here too:

http://www.tanstaafl.co.uk/2012/03/focal-ratio-capture-length-planetary-imaging/

I've approached the problem from a different end I think, but we're both after the same results.

No reason it shouldn't be possible to post pics here unless you need a minimum number of posts before you're allowed to. I'm not aware of that if it is the case though.

James

[mbushell]

James, Very nice and helpful article. I also like your sense of humor.