Tube lens question.... Again...

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Harald
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Location: Steinberg, Norway
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Tube lens question.... Again...

Post by Harald »

Hello,
When putting, say Mitutoyo M Plan APO 5x, on a 70-200 lens. You will then get 5x if the lens is set to 200.
Calculating 5/200=0,025. Does this mean you get 2.5x if the lens is set to 100 (0,025x100=2,5)?
Kind Regards
Harald

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Pau
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Post by Pau »

Yes...with some caveats:

With a zoom from certain focal length downwards you will get vignette.
With my Canon 70-200 f4L IS I can go down to 140mm without vignette on Canon APSC, a 100mm prime would work at least on APSC.
Pau

Harald
Posts: 608
Joined: Fri May 13, 2011 10:33 am
Location: Steinberg, Norway
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Post by Harald »

Thanks Pau,
Does it mean that I can go down to about 100mm on my 7D with the 2.8?
Canon EF 70-200 f/2.8 that is....
Kind Regards
Harald

Lier Fotoklubb / NSFF
AFIAP / CPS
BGF / GMV
http://www.500px.com/blender11

Pau
Site Admin
Posts: 5130
Joined: Wed Jan 20, 2010 8:57 am
Location: Valencia, Spain

Post by Pau »

Harald wrote:Does it mean that I can go down to about 100mm on my 7D with the 2.8?
Canon EF 70-200 f/2.8 that is....
No, it doesn't. It may be better or worse, not easy to guess without testing. This is more related with the lens design and in special the position of its aperture diaphragm than with the maximum aperture
If you have the lens just try it, if not don't buy it just for this purpose.

Likely someone else has tested it and could answer, although I doubt it could achieve 100mm without vignette.
Pau

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