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    Re: Taking the mirror out of the equation
    From: Ken Muldrew
    Date: 2006 Mar 14, 09:21 -0700

    On 13 Mar 2006 at 18:10, cfi@licfi.com wrote:
    >  I taken steps to take the mirror out of my
    > equation by ordering a first surface optical flat mirror from Edmund Comm.
    > Opt.  3" X 4" for $22. Hopefully being a 1st surface mirror will fix my
    > 'blurry'reflected image and being a optical flat from Edmund should take
    > the possible mirror-angle errors out. A couple of quick question before my
    > mirror arrives:
    >       how 'sensitive' is a 1st. surface mirror to (a)placing a light weight
    >       sensitive level on it.
    Are you wondering whether the mirror will bend under the weight of the
    level? If so, I don't think that will be a problem. But leave the level in
    place when you take your sights as removing the level might take the
    mirror out of level.
    > and (b)is there a scratch /corrosion resistant
    >       coating over the aluminization?
    Usually there is, but you can call Edmond to find out for sure.
    > (c) how was $22 as a price?
    Cheaper than Melles-Griot and more expensive than Surplus Shed, but
    nothing to worry over. Before the mirror arrives, I think you should use
    the accuracy of your spirit level to calculate the error in your altitude
    measurement, otherwise you may be surprised with the result.
    Ken Muldrew.

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