Re: ATM [Hist.][Long] Schmidt corrector plates in old televisions/Slumping Schmidt correctors

["Klaas Honders" <k.honders@worldonline.nl>]

Hi Matt,

            The following might be interesting.
Philips used a Schmidt system in a kind of projection tv used in I think in
1950 or so.
It was a box  which contained a Schmidt plate ,a large flat mirror with a
rather large elliptical hole central  in this mirror after this mirror was a
6" spherical
mirror the Schmidt plate measured about 4".
Something like below,

Schmidt plate
       ------------
                     /            I
                    /              I
            hole                 I
                                     I
              /                     I
            /                      I
      flat                        spherical mirror(f/d about  0.67)

 I saw this idea for the first time in Telescope Making #14 in an article
from mr.Sutherland
about the making of a Mak. telescope.
He used the mirror of this set for his instrument after regrinding for a
longer ROC.
I saw a complete set in a museum for old electrical household apparates.
Later I saw 2 complete sets in a dumpstore which I bought for about  $8
each.
They seemed to be in a good state except for one of the Schmidt plates which
showed
a brown coloration.
Later I noticed that this plate consisted of 2 layers one seemed to be a
kind of laquer and
the other was a glassplate the side on which the "laquerplate " was, was
slightly concave.
I don't know how these plates were made.
Maybe by rotation,laquer drying ond plate while this was rotating?
Or by using a masterplate with opposite Schmidt profile?
The spherical mirror was made of low expansion glass,pyrex may be but it is
very hard material.
Harder then Duran 50
The flat plate tested 1/4wave over 2"diameter.

yours

Klaas Honders

k.honders@worldonline.nl