Sept. 2002
President's
Message
Photo FAQs
Photo FAQs
Eric Kissa
Q: Where does the expression "belly button" photography come from?
A: In older days twin-reflex cameras were very popular. The upper viewing lens was held at the chest level and the lower taking lens was not far from the belly button. The habit of keeping the camera at a constant height resulted sometimes in an unfavorable, so called belly button, perspective. After Zeiss introduced the pentaprism, the belly button perspective was replaced by eyelevel photography with its own perspectival distortions.
For a natural perspective, the camera should be as high as the center of the object being photographed.
Q: With archival longevity in mind, can color slides be stored on a CD?
A:No, color slides cannot be stored on a CD, only their scanned image files. Once the slide has been scanned, it cannot be retrieved in its original form. Much information is lost when the slide is scanned because the file size has its practical limits and the color space of the image is changed, usually to the CYMK or the RGB color space.
Kodachrome film has a longevity
of at least 20 years and is an alternative to storing slides on a CD.
Color negatives are less stable than color slides. A CD may be the best
storage medium for color negatives, especially when the files of the scanned
negatives are used for printing anyhow.
Q: I am currently living in Bermuda and saw some of your Q&Aís on The Delaware Photographic Society web page. I have a Pentax ZX-5n with a 135mm f/3.5 lens and a 2x teleextender. The 270mm focal length is still not long enough for bird photography. I am considering the Sigma 70-300mm f/4.0-5.6 DL or APO lens but wonder whether it will be usable (in a manual mode) with a 2X extender.
A:The images obtained by using the Sigma APO 70-300mm lens with the 1.4x and 2x Kenko AF Teleplus PRO 300 teleextenders are acceptably sharp, although the 2x extender is softer than the 1.4x extender. The 1.4x extender also has a larger maximum aperture at the long end of the lens (f/8 versus f/11). In good light my Nikon F100 can auto focus the lens extended to 420mm but this may not be possible with all AF cameras. If the 420mm focal length obtainable with 1.4x extender is not sufficient, then obviously the 2x extender will have to be used. The APO version of the Sigma 70-300mm zoom is sharper than the DL version and this is especially important when using teleextenders.
Optically superior alternatives exist to the 70-300mm + teleextender system but they are more expensive, large and heavy. The Sigma 50-500mm/4-6.3 is a good lens but huge. The single focal length telelenses are large and even more expensive.
Mirror lenses are not popular because of their optical performance, impaired by an uneven light distribution and the fixed lens aperture.
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Send questions concerning photographic
equipment (cameras, lenses, accessories, filters), photographic techniques
(other than digital), and film, as well as information on international
photographic exhibitions, to: ekissa @aol.com.