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Tube lens question.... Again...

 
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Harald



Joined: 13 May 2011
Posts: 564
Location: Steinberg, Norway

PostPosted: Wed Jun 21, 2017 11:26 am    Post subject: Tube lens question.... Again... Reply with quote

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)?
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Harald

Lier Fotoklubb / NSFF
AFIAP / CPS
BGF / GMV
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Pau
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Joined: 20 Jan 2010
Posts: 4805
Location: Valencia, Spain

PostPosted: Wed Jun 21, 2017 2:34 pm    Post subject: Reply with quote

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.
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Harald



Joined: 13 May 2011
Posts: 564
Location: Steinberg, Norway

PostPosted: Wed Jun 28, 2017 10:50 am    Post subject: Reply with quote

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....
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Harald

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AFIAP / CPS
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Pau
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Joined: 20 Jan 2010
Posts: 4805
Location: Valencia, Spain

PostPosted: Wed Jun 28, 2017 11:15 am    Post subject: Reply with quote

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.
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