Re: [ATM] 25" mirror possibilities

["matt" <mariusrf@bellsouth.net>]

>
>
>-----Original Message-----
>  I need to make a sturdy stand before I can set it up for testing.  I have
>held a small led above the mirror at the end of a stick.  The ceiling is
>about 9.5 ft above the mirror surface and with the led at that point, the
>reflected image still appears somewhat larger in diameter than the mirror.
>Consequently I assume that the focal length is greater than 9.5 ft.
>According to what I've read, a Wright Schmidt design would have the
>corrector plate near the focal plane of the primary.  The original
>instrument had the corrector at about 12.5 ft from the primary.
So...that's
>the basis for my guess of about f6 for the mirror.  At least I can be sure
>that it is not really "fast" like f2.5.
>
>Thanks,
>Dennis
>
>

why don't you start with the basics and measure its sagitta ? Not so hard to
use even a makeshift device for that. Just take a straight ruler and place
it across the mirror then measure the depth at the approximate center (from
your long ruler that's resting on the mirror edges to the mirror center) .
That will give you a rough number , but far better than leds on sticks ,
trying to eyeball ceiling image etc.

best regards,
matt tudor

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