Re: 20" Lens/Mirror Blank--What to Do?

Maybe you're thinking of something like this <http://brightbytes.com/cosite/sanfran.html>, where a large (flat?) mirror is used?

Douglas Eagleson wrote:
On Mar 24, 8:39 am, "W. Watson" <wolf_tra...@xxxxxxxxxxx> wrote:
Hi, I'm not sure what this is saying. There is no focal point. It's a flat
blank and transparent blank. Are you suggesting we coat the blank with
reflective material, and put a light in front of it? What will appear on the
screen the viewer can see?
....
- Show quoted text -


A candle flame as the reflected object is commonly used to make the
measure of focal. And even a blank may have some curvature. Measure
it to see. It might have been grond a little and is hardly seeable.

Coating is relativly inexpensive. SO at a minimum you have a blank
low quality mirror if coated as is. You can still use this for a
camera obsura mirror!

A plain flat mirror is a type where the reflection appear the flat
plain and requires a convex transmission lens to expand the rays.
Making the image larger.

The extra lens is expensive.

Here is a modern obscura. Use a small camera from the computer to
magnify. And then you find you still need to do something neat with
the nice lens.

20 inchs is expensive. I guess pick out a place in astronomy history
for blanks.

--
Wayne Watson (Nevada City, CA)

Web Page: <home.earthlink.net/~mtnviews>
.

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