[pure-silver] Re: Large Format Tilt
----- 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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