Small telescope astrophotography site with tutorials

[rcpettengill]

My “not so bad” AstroPhotography & Astronomy site is up. Past the “all hat and no cattle stage”, it’s fast, clean, and full of new content.

All of the images are mine and available under a Creative Commons Attribution-NonCommercial-ShareAlike license.

New feature articles on getting started, earthshine moon photography, and printing astrophotography are in the “How to” section. 

http://astronomy.robpettengill.org/

The site features my astronomical images - mostly made from Austin with a small telescope or camera.
There are seven ways to navigate and discover related images: featured, target, keyword, title, date, shared keywords, 
and shared targets. A  slide show viewer pops up when any image icon in a related photos group is selected.

I have queue of improvements in the works including more “how to” notes”, a full month of lunar images, FAQs, 
and links to full resolution images.

Under the covers: It’s hard to make an image intensive site fast, so I built  an XML model driven, correct by construction, 
static managed site.   It takes less than a second to generate the nearly 200 files in the site from the XML content database. 
On the web, there is no slow wait for hidden database gears to grind or SQL Server error messages.

Let  me know what you think.

[ollypenrice]

I think you'll find that a good number of experienced astrophotographers would disagree with some of your advice. Your calculations based on the Nyquvist theorem, for instance, might be correct in theory but your conclusion that a focal length of 1.35 metres requires pixels below 4.25 microns would find plenty of sceptics. I'd be one. Both guiding precision and the quality of the seeing have a lot to say about useful resolution. Besides, reaching the maximum theoretical resolution is not a prime concern amongst many DS imagers. It isn't always a concern of mine, for instance, though sometimes it is. Getting good strong signal may well be a deeper concern.

At a focal length of a metre (350mm less than in your example) and using pixels of 9 microns (twice the size of those you recommend) one can take images like this. They do not reach the limits of resolution permitted by the sky or the optics but how much does that matter?

I advise against getting the Nyquvist theorem around your neck and, instead, experimenting with the kind of pixel scales which work well from a given setup and a given location. I also advise against going below an arcsecond per pixel unless you know what you are getting into. In the end, it isn't the theory you hang on the wall.

You also say, 'DSOs are a challenge to image on a small scope.' I think you'll find most imagers on here would say the opposite, in effect: 'DSOs are tough to image on a large scope.' That would certainly be the case if the large scope had a long focal length. 

Olly

[rcpettengill]

Olly,

Thanks for your comments and the beautiful DSO images.  My note on resolution matching is aimed at small scopes imaging planets where resolution is very important.  The science of sampling images is well established and if you under sample an image that data is gone forever.  Knowing the limits that nature imposes, guides experimentation in the real world in productive directions.  Paying attention to the right limits for your subject does matter.  DSO photography is very different than planetary photography.  Capturing photons is much more important with DSOs than resolution.  I'll update the note to make it clearer that it applies to planetary imaging and that DSO photographers have different concerns.

;rob

[ollypenrice]

Indeed, the business of planetary imaging is all about resolution. I'm not up on it but doesn't Damian Peach now say he can beat the Dawes limit? None the less, not everyone is convinced that the Nyquvist theorem holds good for light. I have no opinion on that one!

Olly

[rcpettengill]

Remember that Dawes is an empirical limit is based on visual discrimination. The Rayleigh criterion is better defined mathematically, but is still based on assumptions about visual discrimination of detail.  When an image is sharpened using a deconvolution (or wavelet in the frequency domain) based algorithm, then the assumptions of Dawes and Rayleigh do not apply.  It's not hard to to get better than Dawes Limit in images that have been deconvolved with approximate point spread functions.  Even better can be done with measured PSFs.  This is why I use Barlow lenses to over-sample my planetary images.  I get better results than when I just sample at Dawes Limit/2.

I plan to add a note to my site on an easy way to evaluate image resolution (provided that you have a higher resolution image of the same target) and will show an example where resolution is a bit better than Dawes Limit.

It's better to describe the Nyquist-Shannon sampling theorem as mathematics rather than physics.   It does without question apply to any analog measurement that is discretized.  Any confusion about it's validity is probably due to confusion about what it is applied to.  Whenever I see "diffraction limited", I mentally substitute "diffraction limited for visual observation".  The physics of diffraction are straightforward, however they can be reversed, just not by our eyes.

;rob

[RikM]

Hi Rob and welcome to SGL  

If you take a browse around our imaging sections you will find tutorials, tips and tricks and processing hints from some of the best in the game to help you take your astrophotography to a new level. You have made a good start. Keep pushing forward and you will get there