Maximum Detail For Planets?

[BlakPhoenix]

Hi all,


I currently have the 190 MakNewt from SkyWatcher as my main tube and use it with the 290MM & a 2x TV Powermate for my planetary imaging. I'm finding that even with the 2x though the planets are smaller than I would like.


Would there be any benefit of picking up the 4x Powermate? Is there any extra detail that would be gained by doing this, or would the same detail be visible as now, with 2x drizzle in post?


Cheers!

[Stonius]

You want your focal length to be in the range of 6-8m. So you take your current focal length of 1m and multiply it by at least 6 to get in the optimum range. The catch is they only make 5x barlows that I know of.


It's a lot easier with scopes that have FL's closer to 2M where you only have to add a 2 or 3x powermate to get onto the zone.



Of course, then you get into the issues with the brightness falling off and the frame rate increasing along with blur but f the conditions warrant it, you may get some better shots.


since you're already using the 290MM, you won't get pixels that are much tighter than that so changing cameras won't help.


Cheers, Markus

[BlakPhoenix]

Thanks Markus.


I was worried about being detail limited by my aperture. It doesn't sound like this would be the case though? Is there a limit by which adding more powermates wouldn't actually get more detail due to the limiting aperture size?

[Tulloch]

For optimal resolution from your scope, capture with the focal ratio around 5x the pixel size of your camera. So for a 290MM with a pixel size of 2.9 microns, the optimal f/num is around f/15 (see maths below). Since the native resolution of your OTA is f/5.3, aim for a 3x Barlow. or add an extension tube to the end of your 2x to increase the magnification. You might find you are close enough with the 2x as is. You can determine the actual focal length of your system using the equation below (from here (http://www.wilmslowastro.com/software/formulae.htm)).
http://www.wilmslowastro.com/software/images/formula28.png

On the CN website, someone recently posted a series of theoretical images for Jupiter and Saturn based upon the aperture size of your OTA - aperture rules for planetary :)

https://www.cloudynights.com/topic/725085-maximum-resolution-images-for-comparison/

Andrew

[BlakPhoenix]

Thanks Andrew, that's exactly what I was after! Great information to know, and always nice when it can be summarised into one easy to remember formula.