P3D Kingslake's "Optics in Photography" - III

["Dr. George A. Themelis" <DrT-3d@xxxxxxxxxxxxxxxxxxxxxxxxxxx>]

Chapter 7 is about lenses. 

The author writes: "At one time, not long ago, photographers were very 
much aware of the type of lens were using on their camera, and it was 
a matter of price to own a Rapid Rectilinear or some type of 
anastigmat,  Gradually, however, knowledge of lens structure has 
become less important and today most photographers have absolutely no 
idea or interest in the structure of their lenses.  So long as the 
lens has the desired focal length and aperture, priced within their 
means, and gives good definition with adequate depth of field, most 
photographers are satisfied.  This is not a unique phenomenon, as most 
people have no knowledge of the workings of their refrigerators, 
calculators, typewriters [would say computers here] or many other 
appliances of everyday use.  However, there are some how are 
interested in lenses and it is hoped that this chapter will give them 
some useful information."

I could not put it any better.  He then goes on to say that most 
lenses fall into 7 easily recognizable classes and describes them in 
detail:

- Low aperture single-element lenses (inexpensive throw-away cameras)
- Medium aperture 3 or 4-element lenses (most stereo cameras and upper 
  level fixed FL P&S)
- High-aperture Gauss or Sonnar types (modern 50/1.4 lenses)
- Telephoto lenses (long lenses)
- Reversed telephoto (wide angle lenses)
- Zoom lenses
- Catadioptric or mirror systems

Chapter 8 is about "lens Attachments", covering hoods, filters, 
supplementary lenses , afocal, fish-eye, anamorphic, photography 
through a telescope or microscope.

I learned a lot reading about "close-up" lenses.  Did you know that 
the focusing point with a close-up lens is independent of the lens in 
the camera?   For example, if the camera if focused at infinity and a 
+1 diopter lens (positive lens with 1000 mm FL or 40 inches) is 
attached, then the sharp focus is at 40 inches.  With the same lens 
focused at 2 feet, sharp focus is at 15 inches.  If you derive these 
formulas (as I did) then you will know why the FL of the lens is not a 
factor).

BTW, let me say here that a cheap pair of +1 close-up lenses can be 
bought for a few dollars from the drug store as +1 reading glasses!  
You can just stick the glasses in your stereo camera and make it see 
closer!  (This is routinely done with the NimsloÖ use rubber bands to 
hold the glasses in front)

To be continued.... -- George Themelis


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