RE: [APML] New All Sky Camera Images

["Chris Schur" <cschur@cybertrails.com>]

Gene, it is my experience that the f ratio stays the same, and the aperture
decreases considerably.  Skyfog is reached in exactly the same amount of
time as the 50mm lens alone.  but the stars are much fainter.

Chris Schur

Astrophotography: http://www.psiaz.com/schur/astro/index.html


-----Original Message-----
From: owner-astro-photo@seds.org [mailto:owner-astro-photo@seds.org]On
Behalf Of Gene Horr
Sent: Friday, March 08, 2002 2:49 PM
To: astro-photo@seds.org
Subject: Re: [APML] New All Sky Camera Images


Aplanatic@aol.com wrote:

> In general, the f/ratio of the system is increased from that of the camera
lens by
> the following factor:
>
> (1 + 2d/R)
>
> where R is the radius of the sphere and d is the distance from the camera
lens to the
> nearest point on the sphere.

Maybe my brain is drained from work this week, but something doesn't seem
right about this.  Shouldn't the f/ratio be decreasing as you are
effectively
shortening the focal length (assuming that the sphere covers the full
effective
aperture of the lens in use, no adjustment for reflectivity, etc.)?

Gene Horr
genehorr@texas.net

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