RE: [ATM] 4 point mirror cell

["Rod Brackenridge" <rjbr@lycos.com>]

Hi Harro,

Thanks that is encouraging.  I would be interrested in your pictures.  I have some spare guitar tuners but can't imagine how you would use the to adjust the main mirror.  I had not thought of one point being fixed but I it makes sense.  Please let me know when your website is up.

Thanks,

Rod.

> Hello Rod,
> 
> I just finished a rebuilt of my mirrorcell for a similar mirror (12,5 inch,
> 2 inch thick pyrex  f 4,8.)
> Several people on the ATM-list have calculated this mirror in PLOP and they
> all found that a 3-point cell is sufficient !!   Though there is need for
> very small refocus.
> The three points are placed on 0,41*R (65mm) from the centre of the mirror.
> 
> Lately I finished this 3 point cell and the first results look very
> promising. Advantage of a 3-point cell is that it is easy to built and
> therefore very rigid and not too sensitive for building-tolerances.
> In my design I used one fixed point and two points which are adjustable. For
> the adjustable points I used two guitar tuning-mechanisms, which allow to do
> collimation from the side of the mirrorbox (instead of underneath). Another
> advantage is that the collimation can be done  very precise.
> I will place pictures of the mirrorcell on the internet soon.
> 
> Jan van Gastel is using a 4-point-cell for thinner mirrors.
>   This design is also easy to make.
> 
> Good luck
> Harro Treur
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