Jupiter
in [Digital Cameras]
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From: Troy Piggins on 23 Oct 2009 19:46 * Jeff R. wrote : > Troy Piggins wrote: > [---=| Quote block shrinked by t-prot: 19 lines snipped |=---] >> that may have been too long. Maybe should have kept it down to >> 60 secs or so. Jupiter spins so fast you have to get in and get >> out real quick, so you're using as fast a fps as you can get. >> Some guys are shooting 45-60fps. The avi file size I took for >> this was 1.5GB! Just to get a measly little 15kB image! > > Cooled camera? Nope. This one: http://www.theimagingsource.com/en_US/products/cameras/usb-ccd-bayer/dbk21au04/ I'm considering (don't tell my wife) a cooled CCD for longer exposure, deep sky stuff. They're the duck's nuts. But won't be getting the top of the line ones. They go for $10k or multiples thereof. Reckon something like this will do me: http://web.aanet.com.au/~gama/QHY8.html > Hand or auto-guided? No guiding. Not for 90 secs or so. Mount was just tracking sidereal rate on its own. > Suburban location? Country? Centre of Brisbane. Don't think you could find a much more light polluted location in Queensland :( Fortunately light pollution doesn't seem to affect planetary imaging so much because the targets are so bright. I'm talking Jupiter, Saturn, Venus, Mars, even Mercury here. For Uranus and Neptune you use more deep sky imaging techniques I think - longer exposures and light pollution does come into it a bit. This sort of stuff it's more about atmospheric conditions, the jetstream, and scope focus and collimation. I have yet to come to terms with tweaking all that. > (fun, idd'n it!) Oh, ya! -- Troy Piggins
From: Jeff R. on 23 Oct 2009 20:55 Troy Piggins wrote: > * Jeff R. wrote : >> Cooled camera? > > Nope. This one: > http://www.theimagingsource.com/en_US/products/cameras/usb-ccd-bayer/dbk21au04/ > I'm considering (don't tell my wife) a cooled CCD for longer > exposure, deep sky stuff. They're the duck's nuts. But won't be > getting the top of the line ones. They go for $10k or multiples > thereof. Reckon something like this will do me: > > http://web.aanet.com.au/~gama/QHY8.html > Long time since I knew much about them things. ISTR colour didn't exist, and you had to use filters and three exposures with a mono unit. I have patience, but not that much. Waddy'a reckon that unit would retail for? (Any point in asking if you've tried a DSLR ?) >> Hand or auto-guided? > > No guiding. Not for 90 secs or so. Mount was just tracking > sidereal rate on its own. Fairy nuff. > This sort of stuff it's more about atmospheric conditions, the > jetstream, and scope focus and collimation. I have yet to come > to terms with tweaking all that. Even with all that, don't neglect widefield stuff. Point your camera somewhere around Crux, and do a wide-angle shot for a few minutes (piggy-backed, of course) and the results will astound! I couldn't believe how much I could see in a short exposure, even here in the 'burbs where the clouds light up like fireworks from the streetlights. > >> (fun, idd'n it!) > > Oh, ya! :-) -- Jeff R.
From: Ray Fischer on 23 Oct 2009 22:31 Troy Piggins <usenet-0910(a)piggo.com> wrote: >The astrophotography has been keeping me occupied lately. This >is my first attempt at planetary imaging. Lots to learn, I know. >Don't see much astrophotography here so thought I'd share. > >Taken with a 8" f/10 scope with a 2.5x powermate (like a >teleconvertor) giving it an equivalent focal length of around >5000mm. Camera was a DBK21 CCD camera. > >The dark spot is the shadow of one of the moons, and you can just >make out the Great Red Spot at the top. > >http://piggo.com/~troy/photos/2009/2009_10_23/Jupiter091023_1.jpg Pretty nice for an 8" scope. Single shot or composite? -- Ray Fischer rfischer(a)sonic.net
From: Damn 35 F. Rain - Staying Warm Inside Is Winning Today on 23 Oct 2009 23:47 On Sat, 24 Oct 2009 07:21:39 +1000, Troy Piggins <usenet-0910(a)piggo.com> wrote: > > >How does one stop down the aperture of a fixed aperture scope? >The bare scope is f/10. With the 2.5x powermate it becomes an >equivalent f/25. I haven't heard of people using those masks >you're referring to. I'll look into it. Thanks. A simple round hole cut into some opaque plastic, cardboard, or thin aluminum sheeting will suffice. Placed over the opening of your telescope. For a refractor this is easy (no central obstruction). Just place it concentric with the optical axis. For a reflector the choice is not so easy. The secondary mirror's size is optimized for the light path and f/ratio. Larger reflector telescopes can use an aperture mask offset to one side, so as to use an unobstructed region of the mirror between the outside diameter of the primary and the outside diameter of the secondary, and situated between the spider-vanes. Consider too the number of spider-vanes you have. If 4 vanes you will have to cut your mask smaller so its diameter fits within an open quadrant between any two spider-vanes. The huge plus of this for planetary imaging is that now you have an obstruction-free telescope. Of reduced aperture but for bright subjects and due to "seeing" problems this can be a huge plus too. Many people buy 12" or larger reflectors with the intent to only use it as a stopped-down off-axis planetary imager. (8"-10" telescopes too, but you then start to lose resolution due to primary size alone when stopped-down off-axis.) There is a huge cost-savings in buying pre-fabricated easy to make manufactured telescopes much greater than the size needed, as opposed to buying or building an off-axis (asymmetric) reflecting telescope design (see below), or prohibitively expensive refractor of those diameters which is now fraught with CA problems. With the aperture offset you are no longer plagued with diffraction from secondary mirror and its spider supports. Since this is a reflector, you now have a telescope that is free of all chromatic-aberration, making it much better than a refractor of the same size (large and astronomically expensive refractors bought with planetary imaging in mind). Special asymmetric reflector telescopes are designed this way, but grinding and figuring the offset curvatures are extremely difficult and many ingenious methods were tried and found to try to circumvent this fabrication problem. One of the more ingenious is to grind an achromat corrective lens for use with a standard parabolic mirror set at an angle. This achromat ground to the proper figure by using a creative method found for the home telescope builder, but then you introduce CA problems. Often, to simplify things, they'll just buy a much larger pre-figured mirror and then cut it up into 2 or 3 smaller offset-telescope primaries. (I don't think I could bring myself to do that, even though I have the means. It would be like cutting a favorite child into 2's or 3's.) By using an offset aperture mask on a large telescope you now have the best of 3 worlds. An exceptional planetary imager (the same as a prohibitively expensive asymmetric reflector telescope), no CA problems as exists in all refractors, and when the mask is removed you now have a very very nice deep-sky light-bucket. Aside: This is precisely why I chose the size telescope I now have (16" dia.). The 16" also not chosen arbitrarily due to costs nor other issues. When researching I found that due to even the most pristine seeing conditions (unless I am on a mountain-peak), that without adaptive optics the resolution of this size telescope is the same as that of Mt. Palomar's 200" telescope. The weakest link now being caused by the atmosphere itself. There was no appreciable gain in resolution by buying larger. Light-grasp yes, resolution no. (Keep in mind too, this was before image-stacking became popularized to increase resolution. And since I was going to primarily use it for visual astronomy this didn't enter into my decision-making equations. Then, nor now.) Another plus to an offset mask is that you can rotate the aperture-mask to find a "sweet spot" of your mirror where the figure is the most pristine. This can greatly improve on its 1/8th to 1/20th wavelength of light tolerance across its whole surface. For smaller telescopes you can try an aperture reducing mask placed concentric with the axis of the telescope, but then the smaller you stop down the aperture the more that diffraction becomes an issue due to the larger percentage of central obstruction vs. the useful light path. Experiment.
From: Damn 35 F. Rain - Staying Warm Inside Is Winning Today on 23 Oct 2009 23:52
On Sat, 24 Oct 2009 07:30:59 +1000, Troy Piggins <usenet-0910(a)piggo.com> wrote: >* Rich wrote : >> On Oct 23, 11:43�am, Troy Piggins <usenet-0...(a)piggo.com> wrote: >> [---=| Quote block shrinked by t-prot: 14 lines snipped |=---] >>> tweaking of the collimation which should give a sharper image. >>> Will have to try that next time, haven't done it before. >> >> You need at least 25,000mm to really shoot Jupiter. Nice shot at >> 5000mm though. > >Anthony Wesley, the guy who discovered the that most recent >impact scar on Jupiter, takes these sort of shots with an >effective focal length of around 9000mm. > >http://www.iceinspace.com.au/forum/attachment.php?attachmentid=65884&d=1256210105 > >I'd be extremely happy if I can get anywhere near as good as >that. Have you ever tried to image with something of the sort of >focal lengths you're suggesting with back-yard amatuer gear? I'd >love to see examples. Don't mind Rich, he's just a troll that regurgitates what he's read other trolls invent, or he himself invents. He doesn't even own a camera, much less a telescope. Proved many times by many people. He's only here to play "pretend" with his role-play life, using bits and snippets of info that he happens to find anywhere on the net. He believes anything he reads on the net, with no real-life experience to know the difference of when he's being bullshitted. |