Headnote
Before you begin to actually I’d like to clarify two very important points:
First, I am in no case do not call to abandon industrial blends. Not such a costly product that will certainly seek to replace them with primitive homemade. Use a homemade hood should, in my opinion, in exceptional cases, such as:
1. During the journey you have lost or broken proprietary blend and are not able to buy a new one in the near photographic shop.
2. You have decided to take pictures with the old unique lens for which to buy a full-time hood is very difficult or impossible.
3. You are shooting a home-made non-standard lens (eyeglass, camera obscura, etc.)
Secondly, it will not lower the optimal (ideal) blend, and about some simple surrogate substitutes. The proposed product will certainly help to cut off a significant part of the lateral beams, but a certain amount of unnecessary light still penetrates into the lens. Of particular worry in this regard should not be: many proprietary blend also not optimal.
So how does it make?
As a simple alternative to proprietary blend, I propose to use a square lens hood, made of thick black paper or cardboard (eg, black matte paper for watercolor paintings). It is easy to manufacture and very efficient. In addition, a bonded blend of this type can be compactly folded and put, for example, in the wallet.
Fig. 1 shows a scan of such a blend. Drawing is very simple and speaks for itself. The required parameters can be computed by scanning the above formulas. (To avoid trigonometric calculations will help you some typical values of a / r, referred to in Annex 1.) Useful to remember that the focal length of lenses indicated producing firms with some error. Therefore, the calculated value of the angle beta should be reduced by several degrees: Let your hood will be a little wider. (If necessary, use a step by step procedure, as set out in Annex 2.)
The length of the segment and should be equal to the diameter of the rim, which is expected to wear a hood. If the hood is made of not very thick cardboard, it is recommended to cut and do a little less. In this case, when putting the lens hood will have to give it a little barrel distortion, due to which the hood will be a firm hold on the lens barrel.
With regard to the depth of the lens hood (the difference between the radii of two circles in Fig. 1), then a simple rule: the deeper shade, so it effectively. However, very deep blend cumbersome and might hinder the use of other photographic supplies, such as flash. As a quite good first approximation, you can select a depth equal to the diameter of the front lens element.
And what does the pyramid?
The same scan can be used for making paper models of the pyramid (a = 0). For example, for making a reduced copy of the Great Pyramid of Cheops must take the angle alpha equal to 63.4 degrees. Comparing the height of your pyramid with the height of the true pyramid of Cheops (146.5 meters), you can easily assess the scale of the model.
* * *
As we know, the pyramid is often associated with many mystical phenomena. Both inside and outside the pyramids formed special energy field. Therefore, when using the proposed blends should pay attention to any unusual events. Who knows? Maybe you can contribute to the answer to the mystery of pyramids?