Re: [ATM] The Public Terrestrial Telescope Project: An Update

[fhh@npgcable.com]

Re David's post:

> Regarding the optics, the objective will be one of the inexpensive 80mm.
> clear aperture lenses available from the Surplus Shed or Hands-on Optics. As
> of today, I've ordered an F5 from the Surplus Shed ($29.00) and an F7 from
> Hands-On ($59.00). I need to experiment with them to decide which one I
> want.

I have made five 15x80 finders using the Surplus Shed 80mm f/5
objectives.  Five out of five needed to have the lenses flipped
front-to-back in the cell for proper operation.  All five had the
negative element forward, and the positive element rearward.
Perhaps someone in the factory instructed that the "thick" lens
goes in front, and the worker(s) decided that meant the thickness
as seen at the edge (rather than the center) of the elements.

Once my club members helped me figure that out, I found the images
satisfactory.  David, inspect your f/5 objective when it arrives
and see if this might be true for yours.

(Also, bought one at a higher price from Apogee Inc., same cell,
same lenses also needing to be reversed.)

Add the 27mm Kellner Focusable Reticle eyepiece from Meridean
Telescopes, and you have the essentials of a finder with the
focusing done within the eyepiece.  The objective cell needs to
be shimmed up to fit the 4-inch drain pipe at Home Depot;
fortunately, the rim of a Haagen-Dazs pint lid is just right,
so every finder has its sacrificial pint of ice cream in its
construction.  (Your flavor may vary.)

Fred Harris


----------------------------------------------------------------
This message was sent using IMP, the Internet Messaging Program.


_______________________________________________
ATM mailing list http://www.atmlist.net/