[ATM] confusing results

[Saqib Sajjad <saqibsajjad@yahoo.com>]

hello all,


before i plunge into mirror making i want to ask a
question about the last 6" mirror i received from the
vendor.it has bad reflective coating and the thickness
is about 10 mm. i have calculated the focal length to
be no more than 300mm. the sagitta is about 1 mm.
which by calculation should give focal length to be
1452mm. why is it not giving me high focal length ???

is short focal length due to bad reflective coating?
or due to less thickness-diameter ratio ?


Saqib

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