[rollei_list] Re: "Kaligar" Telephoto Accessory lens for Rollei Automat


----- Original Message ----- From: "SandyF" <sbf70@xxxxxxxx>
To: <rollei_list@xxxxxxxxxxxxx>
Cc: <cvug@xxxxxxxxxxxxxxx>; <camera-fix@xxxxxxxxxxxxxxx>; <idcc@xxxxxxxxxxxxxx>
Sent: Saturday, February 25, 2006 1:09 PM
Subject: [rollei_list] "Kaligar" Telephoto Accessory lens for Rollei Automat


A while back, I bought a "Kaligar" Telephoto Accessory lens for my Rollei Automat. I haven't used it for months, and now can't remember if this Accessory lens changes the effective speed of the f/3.5 75mm Tessar, thereby requiring changes in the exposure settings.
If anyone can help, it would be greatly appreciated.
TIA

Sandy F. Ö¿Ö¬

An afocal attachment has no effect on the stop scale. The entrance pupil is magnified (or reduced) in the same ratio as the focal length, so the ratio of its size to the FL remains the same.
The entrance pupil is the image of the stop as seen from the front of the lens. Its size is the _effective_ size of the stop.
This is true for both afocal attachments and for simple diopter mensicus lenses. The difference is that the menicus type has no correction and will introduce aberrations into the optical system where the afocal attachment is at least partially corrected so the optical properties of the system are likely to be better.

---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx

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