Re: Home made Lenses ( soft focus )

Richard is correct, as usual ;-)

I should have said:

The older soft focus lenses, like my/your Wollensak Veritars, are very
simple two element lenses. Nothing more than a couple single element
diopter "filters" (single element "close up filters"). This, given the
current pricing madness, is the joy of John's article. They are simple
and cheap to build!

Filters (above) is in parentheses because a closeup filters (the common
name for them) are really not filters. They are really simple lenses
(usually single element, but Nikon makes a double element close up
"filter" as well).

On Friday, March 4, 2005, at 11:38 AM, Richard Knoppow wrote:

> I don't want to be picky but the meaning of diopter is not a single
> lens element. A diopter is a unit of focal length defined as 1/FL in
> meters, i.e., a lens of 1 diopter has a focal length of 1 meter.
> Diopter measurement is useful where a lens is used primarily in
> combination with another lens as in spectacle lenses or close up
> lenses for cameras. The reason is that the combined focal length of
> two leneses is 1/(( 1/A + 1/B) - 1/D) where A and B are the focal
> lengths of the two lenses and D is the distance between them.
>
> ---
> Richard Knoppow
> Los Angeles, CA, USA
> dickburk@ix.netcom.com
>
--------------
Tom Ferguson
http://www.ferguson-photo-design.com
Received on Fri Mar 4 15:26:10 2005