View Single Post
  #5  
Old 17-05-2012, 12:31 PM
bmitchell82's Avatar
bmitchell82 (Brendan)
Newtonian power! Love it!

bmitchell82 is offline
 
Join Date: Jul 2008
Location: Mandurah
Posts: 2,597
I guess what you guys actually need to start thinking about is not that a certain type of filter magically makes certain emission lines appear. Im sorry they don't.

Light as we know is electromagnetic, but we generally represent it as a sinusoidal wave. depending on the frequency of that wave is depending on what colour our eyes are stimulated to see.

So when you put a UV/IR block filter pretty much anything that lands outside the specified "band range" is stopped.

In an unmodified DSLR the IR block range is letting a TINY amount of hydrogen alpha range which is on the ass end of red but right on the start of Infra red hence half of it is moot.

Sometimes various nebula enhancing filters all they are doing is blocking out big streams of wavelengths which gives the impression that you are capturing more for instance Hydrogen alpha. Truth is your not, its just killed everything else!

This is why narrow band images appear to have so much detail, is the other bands of light aren't filling in the spots where there is no (for instance) Hydrogen alpha.

My advice for you on the Ha, OIII and SII filters for unmodified DSLRs is this.

Your running a RGGB bayer filter. Halpa is in the red neck of the woods hence your really only getting 1 pixel in 4 capturing usable data.

SII i believe is just under Ha and is in the red neck of the woods hence your using 1 piexel in 4 to capture useable data

OIII is in the bluey section of the wave lengths once again your only using 1 pixel in 4 to capture data, with a added smash in the face that OIII is actually hard to get as there isn't that much around!

So you have to start pushing your dslr in the OIII for huge hours of data, with 20+min exposures, your Ha well its like using a 16" telescope but stopping it down to 8". I would either modify your camera to allow the maximum amount of Ha in or just wait and save your dollars for a proper cooled astro CCD.

In saying this the filters will not be 100% useless its just they don't give much return back for time spent as apposed to other cameras. Of course if your handy with Photoshop you can magically make colours appear For reference Ha is not a deep red its more of a salmon red
Reply With Quote