First of all, you would need a very dark sky to avoid sky fog. My last batch of slides were limited to 10 minutes because of the sky conditions. With my two-star alignment with my polar scope, I could have gone up to 30 minutes unguided with my 50mm lens if the sky conditions would of allowed it. A fish-eye lens would be even more forgiving as far as tracking goes. Does your mount have PEC? The best mounts, provided they are accurately polar-aligned and PEC trained, can be left to track unattended and unguided for 30 minutes or more. Of course, the longer exposure the more there is a chance of getting airplane trails. My 2 cents, Debbie
From: Chuck Hards <chuckhards@yahoo.com> Date: 2004/12/07 Tue AM 09:41:29 MST To: Utah-Astro <utah-astronomy@mailman.xmission.com> Subject: [Utah-astronomy] Fisheye lens
Has anyone (Rob? Patrick?) tried tracking fairly long-exposures with a "fisheye" lens? I'm wondering if, guiding on a star near the center of the field, if the edge stars trail because of differential atmospheric refraction? A few years ago I acquired a nice fisheye lens with a FOV darned near 90 degrees, and would like to try it on the sky when the weather warms up. Any meaningful input based on experience is welcome.
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