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# How do the internal elements of a 28-80 mm lens differ from a 28-200 mm lens? Answered

I'm trying to follow an I'ble posted by Patholio (fisheye lens, https://www.instructables.com/id/cheap-fisheye-lens/).
He used an element of a 28-200 mm lens. I have disassembled a 28-80 lens, but the results are less spectacular even though the focal length at the low range (28mm) is the same. I can imagine that the elements of both lenses differ, hence the difference. Is this the explanation?

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## 11 Replies

Yes, the radius of curvature of the lenses is the key to the depth of your fish-eye effect.

Steve

bertus52x11 (author)2010-03-24

So the radius of the element that causes the fish-eye effect in a 28-80 lens would be larger than the radius in a 28-200 lens?

steveastrouk (author)2010-03-24

yup

You could have just said "About 120 mm".  ;-)

bertus52x11 (author)2010-03-26

I'm not sure I understand your comment.

Joke. 200mm - 80mm = 120 mm difference.

bertus52x11 (author)2010-03-27

ok, I get it!  :-)

I never said it was a funny joke....

bertus52x11 (author)2010-03-27

Reminds me of a joke of an old teacher who said: water boils at 100 degrees (C) and not 90, because thats a straight angle.

BobS (author)2010-03-25

I disassembled a 100-300 mm zoom lens, and no fish-eye component came out...

bertus52x11 (author)2010-03-26

But that makes sense...