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Post by zakalwe on Jan 27, 2012 11:04:16 GMT -4
Nice picture. What's your aperture? 80mm at f6.25 Aperture isn't that important in deep-sky imaging. having a fast f-ration (so you can minimize the exposure time) is far more critical. Long exposures need good guiding and also tend to bloat the stars. The longest exposures that I use are 10 minutes (though this was guided with a separate guidescope and software which "locks" on to a guidestar to control the mount), though if I was using narrow-band filters (hydrogen alpha sulphur or O|||) then I'd probably need 20 minutes.
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Post by ka9q on Jan 28, 2012 12:56:06 GMT -4
Thanks. I was comparing your picture with a 18,000 pixel square image of M42 from the Hubble. The Hubble has a 2.4m aperture, an area of about 4.5 m^2. Ignoring obstructions, your 80mm scope has an aperture of .005 m^2, a ratio of 900:1. So if you exposed for 2 hours, then the HST would have needed 8 seconds to collect the same amount of light *if* the fields of view were the same, which they're not. Your picture has a wider field of view, which is another way of saying what you said, that the f-stop is important too. Also, the HST picture seemed to have a longer relative exposure.
The HST has a focal length of 57.6m, so it's f/24 as compared to your f/6.25.
CCDs really have revolutionized astronomy, haven't they?
(edited to add HST f-stop)
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Post by zakalwe on Jan 30, 2012 3:38:45 GMT -4
Thanks. I was comparing your picture with a 18,000 pixel square image of M42 from the Hubble. The Hubble has a 2.4m aperture, an area of about 4.5 m^2. Ignoring obstructions, your 80mm scope has an aperture of .005 m^2, a ratio of 900:1. So if you exposed for 2 hours, then the HST would have needed 8 seconds to collect the same amount of light *if* the fields of view were the same, which they're not. Your picture has a wider field of view, which is another way of saying what you said, that the f-stop is important too. Also, the HST picture seemed to have a longer relative exposure. The HST has a focal length of 57.6m, so it's f/24 as compared to your f/6.25. CCDs really have revolutionized astronomy, haven't they? (edited to add HST f-stop) Yes, yes they have, along with the cheap availability of mass produced optics and tracking mounts. BTW, if youi want to see what's really possible with a small, fast refractor and amateur kit, then look at this image here . It was taken with a 60mm refractor, mounted on a cheap Synta EQ5 mount (albeit with a £3000 camera). Images like this just were not possible by an amateur until relatively recently. Heck, I'd wager that professional observatories would be hard pressed to emulate more than 50 years ago. The imagers website is here:
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Post by ka9q on Feb 1, 2012 4:46:05 GMT -4
Wow, that is stunning. Maybe it's time to dust off my 8" LX200 and shop for a CCD imager. Last I looked you could easily spend several times the price of your scope on the imager...and they were so small...
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Post by zakalwe on Feb 2, 2012 4:25:31 GMT -4
Wow, that is stunning. Maybe it's time to dust off my 8" LX200 and shop for a CCD imager. Last I looked you could easily spend several times the price of your scope on the imager...and they were so small... Whatever you do, make sure your mount is up to it. The mount is THE most important part in DSO imaging. And that image from that guy in Greece is stunning. it's amazing to think that some bloke is his back yard is able to produce an image like that. Professional observatories from not that long ago would have been proud to produce that.
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Post by ka9q on Feb 2, 2012 8:05:07 GMT -4
I have the original (non-GPS) mount with my LX200. Because of this, it's a bit of a pain to align (you basically do the equivalent of an Apollo 'P52' but from scratch) but once it's aligned it seems pretty stable.
I see that it's now possible to just stop sidereal tracking, point the scope at one fixed point on the sky, snap a long series of CCD images and then have software assemble them into a wide panorama as the stars move through your field of view. Wow.
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Post by zakalwe on Feb 3, 2012 5:33:44 GMT -4
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Post by mrspock on Feb 17, 2012 5:23:17 GMT -4
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