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Minus (diopter) lenses used on primes

 
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graphic6x9



Joined: 03 May 2002
Posts: 4
Location: New Orleans

PostPosted: Sat May 04, 2002 5:45 am    Post subject: Reply with quote

I had the great fortune (misfortune?) to have been the purchaser of a set of Spiratone minus (-1, -2, -3, -4) lenses, series VII.

Neither I nor the seller (she wrapped the boxed set in tissue, tied with a ribbon!)have directions for using these lenses.

If memory serves, these lenses provide a telephoto effect when mounted on normal or short tele lenses. Seems like they produced results that were claimed to be no great shakes as far as sharpness and contrast....

However, at under $ 20.00 for the set (on eBay), I wanted to play with them for wide-open, soft focus portaiture.

Any info, comments, or suggestions (no, I will not put them out in the trash) from actual users or knowledgable members will be greatly appreciated.

Thanks,

Wayne C.



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Wayne Catalano
Convention Photo & Video
P.O. Box 96
Chalmette LA 70044
voice/fax 504-271-1507

[ This Message was edited by: graphic6x9 on 2002-05-03 22:48 ]
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Henry



Joined: 09 May 2001
Posts: 1443
Location: Allentown, Pennsylvania

PostPosted: Sat May 04, 2002 2:14 pm    Post subject: Reply with quote

From "Kodak Filters and Other Lens Attachments" (1/52): "Kodak Telek Lenses 1-, 2-, 3-, and 4- produce telephoto effects---fascinating pictures of distant objects---by increasing the focal length of the camera lens. They can be used only with cameras having a ground-glass back and a double-extension bellows or its equivalent. Kodak Telek Lenses are supplied in Kodak Combination Lens Attachments, Series VI and VII only."

From Morgan & Lester, "Graphic Graflex Photography" (10th ed., 1954, p. 30): "Low-powered negative lenses are also available under such names as "Telek," "Telar," and "Distar." These increase the focal length of the lens somewhat and provide some degree of telephoto effect. However, they are only usable where the camera in question has sufficient bellows extension to accommodate the longer focal length resulting. It must be remembered that the additional extension required by these lenses alters the effective value of the marked f-stops of the main lens, and allowance must be made for the effect when calculating exposure. Tables are frequently supplied with the supplementary lens---or the Effective Aperture Kodaguide will serve.

"All simple lens attachments tend to upset the corrections of the camera lens to a greater or lesser extent; to overcome this difficulty it is essential to work only at the smaller lens apertures. The degree of interference with the corrections is greater with the more powerful negative or positive lens attachments."

Comment: all this probably doesn't tell you anything new. My limited experience with the minus lenses led me to earnestly seek out and purchase a long lens, namely, the 203mm f7.5 Optar for my Century. But you never know when you might need the attachment lenses for those "in-between" situations. I'm keeping them in my kit just in case. As for exposure compensation, I use trial-and-error!
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daveblaw



Joined: 11 Feb 2002
Posts: 2
Location: Ohio

PostPosted: Wed Jul 17, 2002 5:54 pm    Post subject: Reply with quote

Wayne, what happened when you tried the negative diopter lenses?

PS: if you want a theoretical explanation of what they do (and a calculator to show you the combined focal length), search on "Gullstrand's Equation"

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