Re: ATM RE: 12" refractor

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

-----Oorspronkelijk bericht-----
Van: Roger Ceragioli <rogerc@dakotacom.net>
Aan: atm@shore.net <atm@shore.net>
Datum: vrijdag 9 juli 1999 19:21
Onderwerp: ATM RE: 12" refractor


>
>Kevin,
>
>Jokes aside, if you look in the March 1978 S&T you'll find an article about
>Jeff Schroder who built an 11" portable refractor.  He used to transport it
>in and on top of his car: the tube rode over the passenger compartment.
>The instrument was, of course, enormous.
>
>The best way to shrink the tube and make the scope more portable is to
>employ two folding flats in an "N" arrangement with the objective at the
>top of the right vertical stalk of the "N", the first flat at its bottom,
>and the second flat at the top of the left vertical stalk.  Tilt the
>mirrors slightly to make the light go through.  This reduces the tube
>length to 1/3 of normal.  And you still view from the bottom up.
>Incidentally, these "flats" don't have to be very flat to work well.  They
>can be curved by several waves and you won't detect the difference in the
>image.
>
>In this way, a 12" ft. tube can be reduced to 4"--much more manageable.
>Still the scope will be heavy--maybe 100 lbs? because of the weight of the
>glass (flint weighs several times as much as crown), the cell, the folding
>flats, and the solid tube itself.  And you'll still need a stout mounting
>and way of elevating the scope up to the equatorial head.
>
>For a really first class scope, you will probably want to buy the glass
>from Ohara or else from Schott directly.  Newport glass sells kits, but
>Newport isn't necessarily reliable.
>
>Personally, I suspect that a very well-made Cassegrain of f/25-30,
>employing a small secondary, aluminum tube that's well ventilated, and
>capped with an optical window will perform as well or better than your
>proposed refractor.  It will also be cheaper, lighter, probably shorter,
>and totally apochromatic.
>
>Good luck, whatever you decide on!
>
>Roger Ceragioli
>
>
hi Roger
            Just read your proposal to fold the lightpath of this 12" ref.
with 2 flat mirrors
In my opinion they should be flat better then 1/10th wave if not there will
be astigmatism .Although a small amount may be unnoticed due the quite
severe chromatic abb. in a 12"  F 12 refractor.(With standart glass)

Greetings,
Klaas Honders
k.honders@worldonline.nl