Help!

Jill Rahn's picture
Here Is A Quick Tip List On Letters For The Help! Desk:
Please confine yourself to only one question per letter. Both postal letters and e-mails are fine, although we prefer e-mail as the most efficient form of communication. Send your e-mail queries to editorial@shutterbug.com with HELP! in the subject header and your return e-mail address at the end of your message. Although we make every effort, we cannot promise to answer every HELP! letter.
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Projector Lens Use
Q. Is there any way to use the projection lenses from slide projectors? I have the regular Kodak and also Navitar 100-200mm lenses. My projectors are in need of repairs, but service and parts are not readily available. It seems a waste to junk at least the Navitar lenses.
Don Riley
via e-mail

A. That’s an interesting question, one that has never come up before in 20 years of writing this column. I’m personally unaware of any other uses for slide projector lenses since they don’t have focusing capability and no diaphragm so they have to always be used wide-open. I contacted several individuals who had been in slide-based audio-visual production for decades but they did not recall any other practical uses for these lenses. One person said they did use some of their excellent old Navitar lenses in LCD projectors after remounting the glass in a new barrel. But he said the newer offerings of LCD projection lenses are equal in quality to the Navitar so they no longer do it. If any readers have found some after-life uses for old slide projector lenses and let us know we will pass the information onto you.
You mentioned needing some parts for your Kodak slide projectors. The folks at Audio Visual Systems (315 S. Green St., Chicago, IL 60607; (312) 733-3370) told me they have a limited number of repair parts for Kodak slide projectors they kept on hand for their projectors and if you know specifically what you need, they might have the part.

Macro Math
Q. Common macro lens sizes include 50mm, 60-70mm, 105mm, and 150mm. Given an f/2.8 lens in any of these models, the closest focusing distances (specifically for Sigma 50mm, 70mm, 105mm, and 150mm) are: 4”, 10”, 12”, and 15”.
At the end of the day, doesn’t this make them about the same, given an increased lens size and an increased minimum distance? So, for all practical purposes, wouldn’t the longest lens be best because you can be more distant from the subject?
Frank Dutton
Many, LA

A. The classic definition of a macro lens is one that has been specifically designed to record relatively flat subjects in excellent detail. Thus they excel when copying flat subjects such as stamps, coins, documents, etc. Most macro lenses are universal in application because they can be focused for distant subjects at infinity then continuously focused right down to about half life-size without need of attaching any accessory (such as a close-up lens in front or an extension tube at the back). The advantage in having a macro lens with a longer focal length (than a normal lens for whatever camera format you are working with) is you don’t have to get as close to the subject to obtain a 1:1 or life-size image of the item. When you are not as close (literally mere inches away with a normal macro lens) it is difficult to direct additional light on the subject for proper illumination.
In addition, when you poke a lens up really close to a skittish subject they can become annoyed or move. You will also have more clearance from parts of a three-dimensional subject such as a flower that might poke the nearby lens. These are the reasons longer focal length macro lenses are preferred over normal focal length macros.
I would like to thank Jack Neubart for his valuable input and comments included in this response. He has worked extensively with many different macro lenses and written about them in his books.

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