[pure-silver] Re: Large Format Tilt
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Thu, 29 Nov 2007 13:16:01 -0800
----- Original Message -----
From: "Helge Nareid" <hn.groups@xxxxxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Thursday, November 29, 2007 12:25 PM
Subject: [pure-silver] Re: Large Format Tilt
BOB KISS wrote:
Forgot to mention (before Richard pounces)...in reality
all of the distances
regarding the lens are measured from the entrance and
exit pupils of the
lens which are not necessarily the same as the physical
surfaces of the
lens.
You don't need Richard for this.
As a matter of fact, for this kind of calculations, the
distances should be measured from the front and rear nodal
points of the lens, which are rarely the same as the
physical surfaces _nor_ the entrance and exit pupils of
the lens.
- Regards
Helge Nareid
The exact locations of the principle planes (same as
nodal points when the entire lens is in air) may be
important for some special circumstances such as micro or
macro work but are not for general work. In any case they
are pretty easy to find as are the locations of the pupils.
I've posted a simple method several times to variousl
mailing lists and to the large-format news group. I will
repeat them here if requested. The measurement requires
determining the exact focal length of the lens. However, if
you trust that the marked focal length is correct the
principle planes are, by definition, one focal length from
the image plane to the lens. Turn the lens around to get the
other one.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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