[LargeFormat] quiet, projects, magnola

[Guy Glorieux]

Frantisek wrote:

>         Clive, wheelie bin is a bit too "huge format" for me :) Although it could
> be the most unconspicious camera around...
>         BTW, do you have any good URLs on wideangle pinholes? What is the max.
> image (degrees) / circle of coverage you can get before vignetting starts?
>

I checked Eric Renner's book "Pinhole Photography - Rediscovering a historic
technique" and it has that information on page 126 (1st edition).  The diameter of
the maximum angle of coverage is 3 times the focal length if you shoot on a flat film
plane.  This means that if you use a 60mm focal length it will cover a circle of
180mm diameter.
Of course, you will lose details as you move away from the center of the image
towards the edges.  This is because the effective f-stop stops down (about 2 stops)
as the distance from the pinhole to the film plane (your focal length) increases
towards the edges, as in the diagram below:

                                        ---  ----        <------Pinhole
                                           /  |  \                     <-|
                                         /    |    \                       |   Focal
lenght = 1X
                                       /      |      \                     |
                                     /        |        \               <-|
                             -------------------------    <----- Film plane
                                    |<----3X----->|           <-----Angle of coverage



So, you can work out the diameter of the circle that will fully cover the emulsion
you want to use and divide it by 3 to get the shortest focal length without
vigneting.

This said, if the shadow area falls in the corners of the image and the highlights
area is in the center, you will have some vigneting if you expose for the average.
If you expose for the shadows on the edges, and want the highlights to come out OK in
the center, then adjust your processing time accordingly.  My own preference with
pinhole photography is to leave some vignetting on the negative.  I can always crop
it in the darkroom.

You should remember that, since the distance from pinhole increases as you move
towards the edges, the focal length will also increase if you use a flat film plane.
With short focal lengths - I use a 4X5 Leonardo camera with a focal length of 1.5 in.
which gives me terrific ultra-wide angles - the change in focal length from center to
edges will create some (nice) distortion in the image.  If you use a curved film
plane, then you will of course avoid both the distortion and the stopping down of the
effective f-stop.

There are several basic Web sites with all the formulas you need to work out the
optimal pinhole diameter depending on focal length.  They will also give you the
effective f-stop of your camera.

You will find all the adresses if you check the "Pinhole photography links" page on
my web site at:
http://www3.sympatico.ca/guy.glorieux/
(remember to click on the british flag to get to the english version).  The links are
towards the bottom ot the menu page.  There are about 5 galleries of pinhole
photography towards the middle of the page, mostly 2 1/4, shot with a modified
Brownie HawkEye camera.

Have fun!

Guy