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Re: [APML] fast optics, even illumination [was: Lagoon and Triffid Region]

To: astro-photo@seds.org
Subject: Re: [APML] fast optics, even illumination [was: Lagoon and Triffid Region]
From: Chris1011@aol.com
Date: Wed, 29 May 2002 13:54:10 EDT
Reply-To: astro-photo@seds.org
Sender: owner-astro-photo@seds.org

In a message dated 5/29/2002 12:29:57 PM Central Daylight Time, matt@starmatt.com writes:

Does anyone have informed opinions about the Ash Lurie 200, which purportedly evenly illuminates medium format?

Is this scope an 8" aperture?

Keep in mind, for even illumination, the light cone at the focal plane is over 3.6" diameter, and with fast focal ratios spreads out very quickly as you move up inside focus. For a mirror system (Newtonian or Cass) it means the secondary mirror might be over 50% of the aperture if you really want 100% illumination in the corners. This means a 25% light loss due to secondary shading right off the bat, not counting mirror efficiencies.

Roland Christen

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