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ASTRO: Milky Way - Sagittarius thru Scutum
A 12 minute exposure with Canon Rebel DSLR and Tameron 28mm-200mm lens
riding on an Orion EQ-1 mount. Taken in Sept 2007 from the shore of Indian Lake in New York's Adirondack Park. George N |
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ASTRO: Milky Way - Sagittarius thru Scutum
George Normandin wrote: A 12 minute exposure with Canon Rebel DSLR and Tameron 28mm-200mm lens riding on an Orion EQ-1 mount. Taken in Sept 2007 from the shore of Indian Lake in New York's Adirondack Park. George N What focal length was it set for? What's the 35mm equivalent for that or does that camera use a full 35mm sensor? I see some distortion to the left on all stars. I wonder is stopping it down a bit would help. That's an odd distortion as it doesn't point to the center but all one way. I saw a shot taken with an NP101 that had the same problem using the same camera so might be after the lens. He was all worried about his NP101 which was brand new as it shouldn't have that type distortion. Yours is worse than his but otherwise looks and acts the same. What happens with a different lens? Rick -- Correct domain name is arvig and it is net not com. Prefix is correct. Third character is a zero rather than a capital "Oh". |
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ASTRO: Milky Way - Sagittarius thru Scutum
"Rick Johnson" wrote
... George Normandin wrote: .....Canon Rebel DSLR and Tameron 28mm-200mm lens......... What focal length was it set for? What's the 35mm equivalent for that or does that camera use a full 35mm sensor? I see some distortion to the left on all stars. I wonder is stopping it down a bit would help. Rick, I generally set the lens at between 35mm and 50mm. Using the manual setting the camera reports the lens is working at F/4. The Tameron lens is designed for the film version of the Rebel so it might not be the best match for the digital camera. I "push" the camera to "ASA 800" which is noisy, but at lower settings the camera hardly records anything in the night sky. I was also using jpg files rather than Canon RAW, which increases noise. Since it's not my camera I don't have the Canon software to read raw's, and they are huge!! The distortion seems be coming from some sort of internal reflection in the system - perhaps from the camera's IR filter or chip cover slip? Bright stars have dim out-of-focus circles off to one side. The chip in this older version of the Canon camera is about the size of APS film - smaller than 35mm film. Finally, I found at the end of that night that the lens was dewed up and I had lost half of the night's work. I never had dewing problems with it before and it was so dark I didn't see the dew until it was too late. This image is processed with drizzle and VanCittert deconvolution to pull out some additional resolution, and then reduced to about 40% of original size (for posting). The original (and huge file) is naturally somewhat better. The camera does have its original "kit" lens designed for a digital camera, but it only zooms to 55mm and is slower. That makes it difficult to focus and polar align the mount. I do both by zooming to 200mm and then back to wide-field. George N |
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ASTRO: Milky Way - Sagittarius thru Scutum
George Normandin wrote: The distortion seems be coming from some sort of internal reflection in the system - perhaps from the camera's IR filter or chip cover slip? Bright stars have dim out-of-focus circles off to one side. I'll pass this on as he was really worried about his new NP-101. Rick -- Correct domain name is arvig and it is net not com. Prefix is correct. Third character is a zero rather than a capital "Oh". |
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