Taken from the forum : http://photography-on-the.net/forum/showthread.php?t=721809
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I'm assuming you're not intending on imaging the Moon and planets only from your comment about a computerized mount. First and foremost I would think about a mount that is capable of good results at such focal lengths. Without one it won't matter what you place on top of it.
To address your lens/scope comparison question depends a great deal on the optical quality of each instrument. Is your 500 a Canon "L" f/4? For discussion sake I'll use it to expand on a few things. The Canon 500L would hold its own very well against Achromat refractors and even some of the ED doublet refractors of the same focal length. It would have an advantage in most cases with its faster focal ratio. But for deep-sky long exposure work you would have to be willing to accept some field curvature(distortion that both refractors and lenses have, visible by distorted stars at edges and corners of images) from the 500 lens since correcting the curvature wouldn't be possible. A refractor or Newtonian(called coma in reflectors) can have this corrected by placing a field flattener/reducer between the camera and the scope. I'm not aware of any that will work for a lens. I use the 1.4X TC for daytime use with my 500L with good results but I don't think I would use it for astro work since some quality would be lost and focal ratio would be increased as well.
One other thing about using a lens is the diffraction spikes you'll see on bright stars. Some people like them some don't, just thought I'd mention it. You can see them here:
http://photography-on-the.net/forum/...hlight=antares
Your 30D will do very well. I use a non-modified 20D and am very satisfied with the results. Once you get a mount that can get you the length of exposures you want you'll need to fine tune alignment and set up skills as well as learn how to best process the exposures you get. There's much to learn so take it slow and continue to do you homework before jumping in too deep. There are plenty of knowledgeable people here that can help so don't be afraid to post any questions you may have.
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I'm assuming you're not intending on imaging the Moon and planets only from your comment about a computerized mount. First and foremost I would think about a mount that is capable of good results at such focal lengths. Without one it won't matter what you place on top of it.
To address your lens/scope comparison question depends a great deal on the optical quality of each instrument. Is your 500 a Canon "L" f/4? For discussion sake I'll use it to expand on a few things. The Canon 500L would hold its own very well against Achromat refractors and even some of the ED doublet refractors of the same focal length. It would have an advantage in most cases with its faster focal ratio. But for deep-sky long exposure work you would have to be willing to accept some field curvature(distortion that both refractors and lenses have, visible by distorted stars at edges and corners of images) from the 500 lens since correcting the curvature wouldn't be possible. A refractor or Newtonian(called coma in reflectors) can have this corrected by placing a field flattener/reducer between the camera and the scope. I'm not aware of any that will work for a lens. I use the 1.4X TC for daytime use with my 500L with good results but I don't think I would use it for astro work since some quality would be lost and focal ratio would be increased as well.
One other thing about using a lens is the diffraction spikes you'll see on bright stars. Some people like them some don't, just thought I'd mention it. You can see them here:
http://photography-on-the.net/forum/...hlight=antares
Your 30D will do very well. I use a non-modified 20D and am very satisfied with the results. Once you get a mount that can get you the length of exposures you want you'll need to fine tune alignment and set up skills as well as learn how to best process the exposures you get. There's much to learn so take it slow and continue to do you homework before jumping in too deep. There are plenty of knowledgeable people here that can help so don't be afraid to post any questions you may have.
__________________
Steve
Canon Gear: 1D Mark II / 5D / 20D / 500L IS (f/4) • 100-400L
My Astro Gallery http://s3.photobucket.com/albums/y67...OTN%20Gallery/
Steve
Canon Gear: 1D Mark II / 5D / 20D / 500L IS (f/4) • 100-400L
My Astro Gallery http://s3.photobucket.com/albums/y67...OTN%20Gallery/
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