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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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