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Old Jan 18, 2003, 1:21 AM   #1
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Default Just got A40 Telephoto lens, questions

I have just got the Canon telephoto lens and adapter for my powershot a40. Whilst playing with it today I noticed that unless I had it on maximum optical zoom when the telephoto lens was connected, the images all enclosed in a "circle" with black around the outside....as you zoom in more this circle gets bigger and bigger until (at maximum zoom) you have a "normal" image again. Is this what it's supposed to be like? surely not? that means that for the telephoto lens if you want a decent picture you are forced to use the maximum zoom to eliminate the "keyhole" effect (I think that is what i'm referring to?) Any help would be appreciated, thankyou.

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Old Jan 18, 2003, 10:09 AM   #2
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What you are seeing is normal for a telephoto lens. The process is call vignetting.

From the digicam dictionary

"Vignetting - A term that describes the darkening of the outer edges of the image area due to the use of a filter or add-on lens. Most noticeable when the zoom lens is in full wideangle. "
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Old Jan 18, 2003, 10:18 AM   #3
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What you're experiencing is vignetting, albeit a very severe case of it. I don't know much about the Canon A40 or the telephoto lens attachment. Only one thing comes to mind is to make sure you have the lens mounted as close as possible to the camera lens, assuming you're using an adaptor tube or ring. Otherwise, I'm clueless.... You may want to consider a different attachment lens, such as the Olympus B-300 which has received very high marks. Take a look at Pemaraal (http://www.b-300.com/index.html) - a well respected site for the B-300 and some nice examples (look at the examples for the A-220 lens (http://www.b-300.com/a200pics.html) and an example of very slight vignetting.)

Good luck.
Paul in NoVA
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Old Jan 18, 2003, 11:14 PM   #4
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Most zoom lenses will vignette if used in wide angle mode, but why would you want to? I understand you want to properly frame your subject, but most folks use the teleconverter to get the largest view of a distant subject possible.

The range of your camera's built in zoom and the range of your teleconverter should overlap in the region where you experience vignetting while using the teleconverter. See if you can't remove the tele lens and frame the shot you want with your camera's built-in zoom.
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