view camera notes

ViewCamera Notes
Jno Cook
http://jnocook.net/vcamera/index.htm
This material is Copyright (c) 1983 - 2006 Jno Cook under the terms of the Creative Commons license. See the [Notice] at the bottom of this page.

Introduction

(Update Mar 2005 - rev 1/06) These notes cover all the aspects of view camera usage except your aesthetic input: Optics, lenses, control of perspective, magnification.
Detailed technical information is found further below. For the benefit of those less inclined to apply math and geometry to everyday life, I have included this 'introduction.' It more or less follows how the course "Introduction to View Camera" at Columbia College, Chicago, is taught.
Zero the Equipment

Learn to level the tripod and the camera when you set them up. Then bring the camera adjustments to a starting point. You will be amazed how much time this saves in the field.
Focus with the back

Don't focus with the front. If you focus with the front, it changes the location from which an image is taken. It doesn't matter much with landscapes and far views, but, with a subject closer to the lens (even portraits) it makes a lot of difference. For extreme closeups it becomes impossible to focus with the front.
The image cone

The lens projects an image in a cone from the rear (and "sees" in a cone at the front). The cone obviously gets larger and larger the further the cone is from the lens. Inside this projected 'image cone' are the images of everything in front of the camera.
Move (focus) the back to find your subject. The back or front can be used to 'frame' the image by shifting left and right or up and down -- up to the point where part of the negative falls outside the image cone.
Learn to inspect the corners of the view screen for coverage by the image cone. Do this by looking through the missing glass corners of the screen. If you can see the light coming through the lens, the image will extend to the corner of the negative -- at the selected f-stop.
In checking focus, note that the edges of the view screen will look dim if viewed by looking directly at the screen. Looking in the direction of the lens -- where the light is coming from -- will make the image appear brighter.
Focal Length

Learn what a 'focal length' is, and know the focal lengths of the lenses you use. Every lens has a focal length measured in inches or millimeters. Know enough to approximate the focal length of your lenses with a finger span. Use a finger span to represent (for example) three or six inches, or use a ruler.
If you know the focal length of a lens, you will instantly know where to place the back at start up. If the film (back) is located one focal length from the (middle of the) lens, the negative will be at 'infinity focus.' All objects which are closer than infinity require moving the back further away from the lens to bring them into focus.
Dead Zone

The focal length of a lens also determines a 'dead zone' where you cannot make an image, and you cannot focus on an object. This is the region from the lens to one focal length in front of the lens (cannot focus), and the region from the lens to one focal length behind the lens (cannot make an image).
Remembering this will avoid a lot of needless racking back and forth to 'find' an image, but can also be used as a quick check on how much to extend the back to bring a close-up object into focus.
Use Newton's formula (developed 300 years before photography!). Newton's formula is:
a * b = F^2

Where 'a' and 'b' the distances in front of and behind the lens, but measured beyond one focal length in front of or behind the lens, and F is the focal length of the lens.
If you think focal lengths, then F^2 reduces to 1. Thus:
a = 1 / b

Where 'a' and 'b' the distances in front of and behind the lens, but measured in 'focal lengths' and, again, each represents the distance beyond one focal length in front of or behind the lens.
Example: if your subject is 6 focal lengths in front of the lens (thus 5 FL beyond the dead zone), the bellows will be extended 1 plus 1/5th focal length. This works in reverse with enlargements also.
Same Size images

Image reduction (or enlargement) is simply the ratio of the total distance in front of the lens divided by the total distance behind the lens (with the object in focus).
If the object and the negative are located 2 focal lengths in front of the lens, and 2 focal lengths behind the lens, the image will be the same size as the object.
Simple, except for the fact that focusing is nearly impossible at this 1:1 ratio. It is best to set the back to exactly two focal lengths, and then slide the object into focus.
Do that by first focusing on something far away, and mark off the focal length of the lens on the front and back standard (on pieces of masking tape stuck to the front standard and the back standard). Then set the back standard at two focal lengths by measuring two focal lengths between the front mark to the rear mark.
Extreme Close-ups

If the object moves closer than two focal lengths in front of the lens it will result in an enlarged image. The maximum enlargement will happen at the edge of the front 'dead zone' -- the image would become infinitely large (and the bellows would be infinitely extended). In this case it is also much easier to focus by sliding the object back and forth, rather than attempting to focus with the back.
If you want to make a maximum enlargement, use the shortest lens you have, extend the back all the way, and measure the total bellows extension from the lens. Subtract one focal length for the dead zone. That will leave you with a magnification about equal to the remaining focal-lengths.
As an example: Using a 3 1/2" lens, with a maximum bellows draw of 14" (not untypical for a studio camera), you have 14" of bellows extension. Divide 14 by 3.5 gives you '4' -- subtract 1, and that will be the magnification. That is right: the image will be (about) 3 times as large as the object.
The inverse of the '3' -- the three additional focal lengths that the back is extended beyond the rear dead zone -- will be the location of the object beyond the dead zone in front of the lens -- also measured in focal lengths. So, for this example, 1/3rd focal length beyond one focal length. One third of 3.5" is about one inch. So the object is located at 3.5 + 1 = 4.5" in front of the (middle of the) lens in order to be in focus.
Bellows Extension Compensation

Light falls off rapidly when the back moves away from the lens. The notes below reduce all the calculations to simple notions: You need to add one stop when the bellows are extended a half focal length beyond infinity (beyond the rear dead zone), and two stops when it is extended one full focal length beyond infinity. After that add one f-stop for each additional focal length that you move the bellows further from the lens.
But do not change f-stops, change time instead.
Swing and Tilt of the Back

The back is used to 'shape' an image. You can change the perspective and the size with the back. You can make trapezoids look like rectangles. You can make buildings assume radical up-down or left-right perspectives. You can also compensate for buildings which cannot be photographed except from an angle.
But when you swing the back (for example) the image at the right and left will go out of focus. The center will stay in focus, because the center of the film plane will still be the same distance from the lens. The left and right will be either further from the lens (and thus out of focus) or closer to the lens (and thus out of focus).
On some cameras the center will not stay in focus because the back does not rotate on a line through the film. So, make a small adjustment in focus.
Then return the focus to the left and right side (for the above example) by rotating (swinging or tilting) the lens in the opposite direction from the swing or tilt of the front. Again, since on some (if not most) cameras the rotation does not happen at the center point of the lens (the 'rear nodal point'), there might be some shift in the focus at the center. Fix that, and continue rotating the lens. You will see the left and right pop into focus. Amazing!
Nice? but check for lens cut-off, for it is possible to swing the lens enough that part of the back falls outside of the image cone.
Swing and Tilt of the Front

Except to correct focus, the swing and tilt of the front standard does nothing. The image stays in the same place -- the same place on the negative. The image may be cut-off as the image cone swings away from the center of the negative. It does not even make the image go out of focus (a little if the axis of rotation is not correct). But this principle can be used to make panoramic images, by rotating the whole camera about the axis of the rear nodal point of the lens.
Shift and Rise-drop of the Front or Back

Shifting (left-right) or raising (or dropping) of the front or back simply shifts the image left-right or up-down. Do this with the back to make small adjustments in composition. The front has much more effect, and is used by portrait photographers to compensate for the height of subjects -- without having to raise or lower the tripod.
I would recommend you do not shift (or raise / drop) the front or back when you are using swing and tilt unless you can imagine exactly where the image from the center-line of the lens will fall at the back, and can mentally compensate for it.
Technical Notes

To download all the files as a zip file click [http://jnocook.net/vcamera/vc.zip] and download. This is a large DOS/Win or Unix zip file (compatible with Unix/Linux/OSX, VMS, OS/2, DOS, various Windows, Minix, Atari, Macintosh, Amiga, and Acorn RISC OS, and compatible with Phil Katz's PKZIP for MSDOS systems). It contains this page, the gif files (in a directory labled 'bin'), and the depth of field tables as text files -- 339 KBytes total. After downloading save it to some directory you can remember, unzip, and then use your browser to point to the index.htm file to read and view.
Almost all the "pages" below are giant image files. You may want to print the images individually, for the complete page is 340 Kbytes.
Jump to various topics below..

[1: nomenclature, movements]
[2: focal length, image limits, 1:1]
[3: image cone, cutoff]
[4: normal lenses, perspective]
[5: plane of focus]
[6: rotating the lens and film plane]
[7: photographing the Giza pyramids]
[8: basic perspective control]
[9: lens to film and lens to subject distances]
[10: magnification]
[11: bellows extension factor]
[12: long and wide lenses]
[13: image resolution and f-stops]
[14: hyperfocal distance]
[15: depth of field]
[bellows factor and depth of field tables]
[16: closeup lenses and changing focal length]
[17/18: image location]

Bellows Factor and Depth of field Tables

These are available as separate text files, as follows

[Bellows factor] for 6 and 3.5 inch lens
[Critical DOF] for 6 and 3.5 inch lens
[Close focus DOF] for 6 and 3.5 inch lens

This material is Copyright (c) 1983 - 2005 Jno Cook. You may redistribute or modify this material under the terms of Creative Commons license. A copy of the license is included on the page entitled Creative Commons Deed 2.5

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