Re: Home made Lenses ( soft focus )

----- Original Message -----
From: "Michael Briggs" <MichaelBriggs@earthlink.net>
To: <alt-photo-process-l@sask.usask.ca>
Sent: Sunday, March 06, 2005 8:14 PM
Subject: Re: Home made Lenses ( soft focus )

>
> On 04-Mar-2005 Tom Ferguson wrote:
>>
>> 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.
>
>
>> On Friday, March 4, 2005, at 11:33 AM, John Cremati
>> wrote:
>
>>> Tom,
>>> I believe the commercial Soft Focus Lenses go
>>> far beyond the
>>> mounting two or 3 diopter lenses in a barrel.... As a
>>> example the lens
>>> which
>>> I had purchased is a color corrected Wollensak
>>> Veritar. It is a 3
>>> element design engineered to reduce chromatic
>>> aberration , so it is
>>> suitable for color. It achieves its softness by
>>> controlled Spherical
>>> aberration...
>
> The resolution is that the Veritar consists of 3 elements
> in 2 groups. This
> is what is shown in the cross-section view in an original
> Wollensak brochure
> that I have. The number of elements is confirmed by
> shinning a flashlight at
> the two groups: the front shows two reflections, while the
> rear shows three.
> There is more to the design of the Veritar than placing
> two single-element
> lenses on each side of the aperture. AFAIK, Wollensak
> only used this design
> for the Veritar. You can check yours with a flashlight --
> unscrew the groups
> from the shutter and count the reflections.
>
> --Michael

 This is interesting. Kingslake states that the Veritar and
Verito were "simple uncorrected lenses similar to the
Steinheil Periskop." Obviously, he was wrong about this.
Its hard to know why the compounding was done. Perhaps for
chromatic correction but it also may have been for other
reasons. A cemented surface can be used to either correct or
generate spherical aberration. A cemented doublet can also
mimic the properties of some unavailable glass type.
  The more complex structure of these lenses helps to solve
the puzzle of why they have such a unique reputation.

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