After my recent foray into Astrophotography, last night I thought I'd go back to basics with just a telephoto-lens and see how that compares with a telescope on something relatively easy Astrophoto-wise, the Orion Nebula, M42.
Here's an image taken through my Sigma 150-500mm tele-zoom at 500mm, with an EOS 6D, both mounted on a telescope tracking mount so that I didn't get star-trails during the 1 minute exposures.
I took 57 x 1 minute exposures at f/8 ISO800 and stacked them using a piece of software called Nebulosity. The same software was used to de-noise the images, using a technique called dark-frame subtraction, whereby you take a number (twenty in this case) of dark images with the lens cap on, average them to determine where any "hot" pixels are located and whether you have any non-random noise, and then subtract this noise-information from each of the original captures.
Nebulosity then "stretches" the images dynamic range in a fashion akin to Photoshop's levels adjustments, so that the minute differences between the darkest and lightest areas of the image are stretched to utilise a much greater proportion of the histogram (exaggerating small differences so they become visible). I then used Lightroom to crop, adjust, sharpen and tidy the images, and finally the oft-maligned Photomatix to pullout even more detail from the image.
Below the tele-zoom image is the previous weekend's telescope image for comparison. Considering that the tele-zoom image was captured with the half-moon pretty close, washing-out the sky, I'm pretty pleased with the result! The fine-detail isn't so obvious, and the colours are far more muted, but overall I'm pleased with how much has been captured with basic equipment :)
EOS 6D, Sigma 150-500mm @ 500mm, 57 x 1 min @ f/8 ISO800
M42 Sigma by S.J.P, on Flickr
EOS 6D, Celestron 750mm focal-length telescope, 40 x 1 min @ f/5 ISO800
M42 Tonemapped by S.J.P, on Flickr
Here's an image taken through my Sigma 150-500mm tele-zoom at 500mm, with an EOS 6D, both mounted on a telescope tracking mount so that I didn't get star-trails during the 1 minute exposures.
I took 57 x 1 minute exposures at f/8 ISO800 and stacked them using a piece of software called Nebulosity. The same software was used to de-noise the images, using a technique called dark-frame subtraction, whereby you take a number (twenty in this case) of dark images with the lens cap on, average them to determine where any "hot" pixels are located and whether you have any non-random noise, and then subtract this noise-information from each of the original captures.
Nebulosity then "stretches" the images dynamic range in a fashion akin to Photoshop's levels adjustments, so that the minute differences between the darkest and lightest areas of the image are stretched to utilise a much greater proportion of the histogram (exaggerating small differences so they become visible). I then used Lightroom to crop, adjust, sharpen and tidy the images, and finally the oft-maligned Photomatix to pullout even more detail from the image.
Below the tele-zoom image is the previous weekend's telescope image for comparison. Considering that the tele-zoom image was captured with the half-moon pretty close, washing-out the sky, I'm pretty pleased with the result! The fine-detail isn't so obvious, and the colours are far more muted, but overall I'm pleased with how much has been captured with basic equipment :)
EOS 6D, Sigma 150-500mm @ 500mm, 57 x 1 min @ f/8 ISO800
M42 Sigma by S.J.P, on Flickr
EOS 6D, Celestron 750mm focal-length telescope, 40 x 1 min @ f/5 ISO800
M42 Tonemapped by S.J.P, on Flickr
Of course, if you think of them as a set of tubular steel legs, a couple of bearings, and two lego-motors then they're ridiculously expensive 
They're also far cleverer than your common-all-garden photography tripod in that they know where everything interesting is located, so tell it where you are and what the time is, and in the press of a couple of buttons the tripod moves itself off to align with whatever you've selected - magic!
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