Determining exposures for the pinhole camera

Brian Young shows us how to measure our exposure times for our pinhole cameras a little more precisely than “bright sun” or “hazy sun”.

Introduction

The purpose of this short article is to encourage pinholers to adopt an objective means of determining the long exposures required for pinhole cameras. The subjective “bright sun, hazy sun” approach is all very well but it lacks rigour.
The method is based on extrapolation of the familiar EV Chart (see below). Imagine this chart being extended downwards for ever-increasing f-numbers and to the left for ever-increasing exposure times until we are in a region of interest to pinholers.

EV chart exposureThe EV Chart was conceived for use with lensed cameras which may be set to a variety of f-numbers. With a pinhole camera, the f-number is fixed and this introduces a major simplification which makes the task of extrapolation much easier. Instead of a 2-dimensional EV Chart for a particular film sensitivity, we have 1-dimensional EV Line.
Extrapolation works for any negative as long as reciprocity holds. Fortunately, in the author’s experience, film or paper sensitivities of ISO 25 or less do not appear to exhibit reciprocity failure, even for exposures of several minutes.

The Exposure Table

An Exposure Table will be found at the end of this article. Here there are exposures (in seconds) for a typical paper negative with a sensitivity of ISO 12.5. Across the top of the table are a range of f-numbers (N) in half-stop intervals from 45 to 1024. Down the left-hand side are exposure values (EV) from 7 to 16 in steps of 0.5. You are free to interpolate if your f-number doesn’t happen to be one of those shown.

"Am Knieproderstrasse" by Brian Young.

“Am Knieproderstrasse” by Brian Young. This picture was shot with my Black Box camera (f = 175mm, d = 0.5mm, N = 350) on Adox Pan 25 ISO 4in x 5in cut film. EV was 13.5 and exposure was 42s.

Thanks to the assumption of reciprocity, the table can be used for other film or paper sensitivities. For example, some papers have a sensitivity around ISO 6 (one stop down from 12.5) so you will double the time shown. My favourite 4in x 5in cut film has an ISO of 25 (one stop up from 12.5) so I will halve the time. If you use ISO 100, then divide the time shown on the table by eight.

Finding the EV

If you have a light meter, well and good, since they measure EV directly. Just make sure that you set the film speed to 100 ASA or ISO. You can often find good light meters in flea markets; don’t buy a Russian one since they use the GOST standard.

A conventional camera may also be used as a light meter. Set the ISO to 100 and read off the aperture and shutter-speed readings. Then enter the EV Chart for ISO 100 (above) to find EV for the scene.

Set your camera to show half-stops in aperture and/or shutter speed and you will end up with half-stops for EV, which is fine. Some cameras offer an option of one- or two-thirds stop intervals which should be declined.

I do hope that you find the EV approach to exposure useful and rewarding. Happy pinholing!

Exposures (in seconds) for 12.5 ISO paper negatives

f-number in half-stop intervals

EV

45

54

64

76

91

108

128

152

181

215

256

304

362

431

512

609

724

861

1024

7.0

128

181

256

362

512

724

1024

7.5

91

128

181

256

362

512

724

1024

8.0

64

91

128

181

256

362

512

724

1024

8.5

45

64

91

128

181

256

362

512

724

1024

9.0

32

45

64

91

128

181

256

362

512

724

1024

9.5

23

32

45

64

91

128

181

256

362

512

724

1024

10.0

16

23

32

45

64

91

128

181

256

362

512

724

1024

10.5

11

16

23

32

45

64

91

128

181

256

362

512

724

1024

11.0

8

11

16

23

32

45

64

91

128

181

256

362

512

724

1024

11.5

6

8

11

16

23

32

45

64

91

128

181

256

362

512

724

1024

12.0

4

6

8

11

16

23

32

45

64

91

128

181

256

362

512

724

1024

12.5

3

4

6

8

11

16

23

32

45

64

91

128

181

256

362

512

724

1024

13.0

2

3

4

6

8

11

16

23

32

45

64

91

128

181

256

362

512

724

1024

13.5

1

2

3

4

6

8

11

16

23

32

45

64

91

128

181

256

362

512

724

14.0

1

2

3

4

6

8

11

16

23

32

45

64

91

128

181

256

362

512

14.5

1

2

3

4

6

8

11

16

23

32

45

64

91

128

181

256

362

15.0

1

2

3

4

6

8

11

16

23

32

45

64

91

128

181

256

15.5

1

2

3

4

6

8

11

16

23

32

45

64

91

128

181

16.0

1

2

3

4

6

8

11

16

23

32

45

64

91

128


Beginners guide to pinholing
From pinhole to print – Inspiration, instructions and insights in less than an hour
by Gary Fabbri, Malin Fabbri and Peter Wiklund
The quick and easy way to learn how to build a pinhole camera!
From pinhole to print will guide you from drilling your first pinhole to printing your first pinhole photograph. It is an easy to read, step-by-step guide to making a pinhole camera and creating images.
Strongly recommended for beginners

3 Trackbacks

  1. […] Determining exposures for the pinhole camera (alternativephotography.com) […]

  2. […] Determining exposures for the pinhole camera (alternativephotography.com) […]

  3. By Lochkamera | wer bastelt mit? on May 11, 2014 at 4:59 am

    […] Die Blende (f) errechnet sich sie folgt: f = Brennweite / Lochdurchmesser z.B. Brennweite: 130mm (13cm), Lochdurchmesser: 0,5mm 130 / 0,5 = Blende 260 Das ist ja sehr nahe bei “Standardblende” 256. Allerdings muss bei der Belichtung noch der Schwarzschild-Effekt (engl.: reciprocity failure) berücksichtigt werden. Dieser ist bei unterschiedlichen lichtempfindlichen Materialien sehr unterschiedlich – Ausprobieren ist nötig. Die Blendenreihe (in den “höheren Regionen): f/16 f/22 f/32 f/45 f/64 f/90 f/128 f/180 f/256 f/360 f/512 f/720 f/1024 AlternativePhotography.com: Belichtungstabelle für Pinhole-Kameras […]

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