[LargeFormat] Macro photography and movements

[Mike Finley]

On Sat, 31 Jan 2004 14:46:19 -0800, "Paul Butzi" <photo@butzi.net>
wrote:

>> However, at 1:1 magnification the point of focus to film distance is
>> at a minimum for conventional cameras. Whether you increase or
>> decrease .or the lens to film distance, the focus point moves further
>> away from the film. Its this that makes me wonder what happens on a
>> large format camera.
>
>
>I don't understand.  On any camera with a lens that has a fixed focal =
length
>(e.g. no moving internal elements that change focal length as you =
focus),
>increasing the lens to film distance DECREASES the lens to subject =
distance,
>as described by the lens rule:
>	(1/f) =3D (1/v) + (1/u)
>Where f is the focal length and v and u are the lens to film and lens to
>subject distances.
>
>When u =3D f and v =3D infinity, you are focused at infinity and the =
bellows
>extension is the shortest it can be and have something in focus - focus =
is
>at infinity.  As you increase the bellows extension (increase the lens =
to
>film plan distance) the distance to the subject in focus decreases.  =
When u
>=3D v =3D (2 * f) you have the bellows extended to twice the focal =
length, the
>lens to subject distance is twice the focal length, and the =
magnification is
>1:1.  If you increase the bellows extension from that point, you =
continue to
>decrease the lens to subject distance and increase magnification.
>
>No matter what magnification you start with, increasing the lens to film
>distance will always increase magnification and shorten the lens to =
subject
>distance.
>
>At no point is it possible to move the film farther away from the lens =
and
>increase the lens to subject focus distance.
>

Agreed, but I was talking about the film to subject distance, not lens
to subject. I'll try to put it another way:

If you start with film and lens parallel, at 2xf, then the plane of
focus is 4xf from the film, or 2xf from the lens.

Where is the plane of focus if you then tilt the lens (using an axis
tilt)? Is it still a plane, with one part closer to the minimum
focussing distance for a conventional camera (ie film to subject less
than 4xf), or is it curved, with the focus at 4xf on axis, and further
away than 4xf both above and below?


Mike Finley, http://www.efikim.co.uk