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How to make a simple lens hood?
Recalling ancient pyramids
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Introductory notes

1. I am not going to convince you that home-made hoods are always the best solution. On the contrary, I believe, a good lens hood from a reputable manufacturer should always be your choice. Hoods are not that expensive to be manufactured at home. However in rare cases, a home-made hood can be the only available hood. For example,

- you may loose or break one of your regular hoods during your travels;
- you may want to experiment with an old lens, for which no hoods are available on the market;
- you may want to make a hood for your pinhole camera; etc.

2. This article does not deal with optimal hoods. Instead, it offers a rough substitution. Nevertheless, even such inexact things can be efficient enough.

How to make a simple lens hood?

The square hood, I am going to describe, is made from thick black paper or cardboard. For example, thick black paper for watercolor paintings will perfectly do. Such a hood is quite efficient and easy to make. Moreover, it can be folded easily, after which it will become almost flat. You may carry it in your wallet, if you like.

	f stands for the focal distance of your lens; d is the equivalent diameter of film frames d = 51mm in 35mm photography d = 85mm for frames 6x6cm (medium format) _______________________________________ Important Notes! 1. d is not 43mm for frames 24x36mm 2. tg stands for tangent TAN()
Fig. 1

The diagram in Fig. 1 is self-explaining. All the angles and other parameters can be calculated from the above given formulas. (Several frequent cases from Appendix will help you to avoid trigonometric calculations.) However, you should keep in mind one important fact. Manufacturers typically do not inform us about precise values of focal distances of their lenses. Thus, I recommend that you should make your hood a bit wider (slightly larger alpha) to secure your shots against vignetting.

The length of the line a should be equal to the diameter of the cylinder, onto which the hood is going to be installed. If the paper is not too thick, I recommend the line a be slightly smaller. In this case, a certain barrel deformation of the hood will be required to install the hood onto the lens, but the joint will be more reliable.

As far as the length of the hood is concerned (half of the difference between the two diameters in Fig. 1), I would say the bigger the better. However, very big hoods are bulky. As a good starting point, you may make your hood as long as the diameter of your lens.

		Fig.2 demonstrates an example of such a hood. In this particular case, the hood is attached to the pinhole lens, which is described in detail in another article “A pinhole camera based on a Pentax SLR camera”.
Fig. 2

Is there any connection between hoods and pyramids?

The hood I am describing here can be considered as a part of a pyramid, as you may guess. If a = 0, the diagram in Fig. 1 allows you to build a small paper model of a pyramid. For example, if you want to make a model of the Great Pyramid of Cheops at El Giza, Egypt, you should set alpha = 63.4 degrees. The height of the actual pyramid is 146.5 meters (ca. 480 feet). Compare it to the height of your model and determine the scale. * * * Pyramids are mystical things. Some sources claim, certain energies are accumulated both inside and outside pyramids. Thus, be prepared to meet any unusual phenomena, when using the lens hood from this article.

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APPENDIX

a/r ratios for several frequent cases

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