Re: Home made Lenses ( soft focus )

----- Original Message -----
From: "Tom Ferguson" <tomf2468@pipeline.com>
To: <alt-photo-process-l@sask.usask.ca>
Sent: Friday, March 04, 2005 1:35 PM
Subject: Re: Home made Lenses ( soft focus )

>I agree that soft focus lenses are unique. Each model seems
>to do something different :-)
>
> I had never heard the term "Mechanical" versus "Chemical"
> focus. I wonder if the "Chemical" isn't focus shift as you
> stop down. I've always focused soft focus lenses ate the
> F/Stop I was going to shoot at (I'm not sure where I was
> taught that).
>
> I've never seen a three element color corrected and coated
> Veritar! My 10 inch is two single uncoated elements with
> nothing but space and an alphax shutter between them. My
> other Wollensak soft is a longer Verito. Similar
> construction, but HUGE. About 4 inches by 7 inches in
> size.
>
> On Friday, March 4, 2005, at 11:33 AM, John Cremati
> wrote:
>
>> The older soft focus lenses, like my/your Wollensak
>> Veritars, are
>>> really just a couple diopters. Very simple two element
>>> lenses. A
>>> diopter is simply a single lens element. This, given the
>>> current
>>> pricing madness, is the joy of John's article. They are
>>> simple and
>>> cheap to build!
>>
   Chemical focus is a very old term from the days when
plates were sensitive only to blue and UV light and lenses
not very well chromatically corrected. Chemical focus is
contrasted to visual focus. When focused by eye on the
ground glass these lenses could be noticably out of focus
for the blue light the plates were sensitive to. Decent
chromatic correction has been possible for nearly 120 years.
Further orthochromatic and panchromatic materials show best
focus at the same point as best visual focus.
   Most of the classic soft focus lenses are pretty well
achromatized. A few very early soft focus lenses used
chromatic aberration to get the soft effect but these are
not suitable for color work nor did they prove to be very
popular even when new.

---
Richard Knoppow
Los Angeles, CA, USA
dickburk@ix.netcom.com