[pure-silver] Re: Large Format Tilt

Richard Knoppow wrote:

[... big snip ...]
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. 

Sorry Richard
You are of course right - I was being somewhat excessively pedantic in my previous post. One definition of a nodal point is that the image does not move if the lens is rotated around the nodal point, that is indeed equivalent to the nodal point being exactly one focal length from the focal plane (at infinity). This can actually be moderately useful for large format photography, in that if your lens is mounted in such a manner that the rear nodal point coincides with the rotational axis of the front standard, there will be minimal requirements for reframing and refocusing with a lens tilt or swing. However, this is rarely the case with any practical camera/lens combination.
However, having worked with bottom tilt axis, central tilt and swings axes and asymmetrical axes (as used by Sinar), I will concur with the advice that you really need to check your focus with a high magnification loupe on the ground glass - don't trust any of that fancy stuff.
Of course, for any movements, it helps if the swing or tilt axes are actually within the image area - bottom tilts always require refocusing of the entire image, which can be a right pain at times.
Personally, I tend to prefer front tilts and swings - rear movements do affect the perspective of the image (as in converging lines). As for shifts, except for close range work, it doesn't really matter which standard you use.
Finally, any rear swing or tilt can be shown to be equivalent to a front swing/tilt combined with a camera rotation and a shift (and for that matter vice versa). The proof of this can be left to the student ... 

- Helge Nareid
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