ef 25-2

yooperdooperyooperdooper Registered Users Posts: 231 Major grins
edited June 12, 2011 in Cameras
hello:i have a cannon eos 30-d with a canon efs 18-200mm lens.recently i bought an extension tube made by canon an ef 25-2.it worked well when i tested it.my question is how much does it increase the focal length.?does it increase the focal length equally from 18mm to 200mm?can i use it for more than just macro? thanks john

Comments

  • craig_dcraig_d Registered Users Posts: 911 Major grins
    edited June 5, 2011
    Extension tubes don't change focal length. They just move the lens farther away, which allows you to focus more closely (at the cost of no longer being able to focus to infinity, or in fact, very far away at all). Focusing more closely effectively increases maximum magnification, which is why extension tubes are usually thought of as macro tools.

    The effect of an extension tube is greater with shorter lenses, so you might think that your zoom lens would get greater magnification when zoomed out. However, zoom lenses are tricky devils, and they often don't do what you might expect when put on an extension tube. Since you already have both the tube and the zoom lens, you may as well experiment to see what happens. But you might want to pick up a prime lens or two, probably starting with the ultra-cheap Canon EF 50mm f/1.8 II, if you want to do macro photography with extension tubes.
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  • yooperdooperyooperdooper Registered Users Posts: 231 Major grins
    edited June 6, 2011
    experimenting
    today i expeimented with both the canon 18-200mm and the sigma 18-50 mm using the ef 25-2.the longer lens did better in terms of focus on the flowers i shot but the focus wasn't real good.i held the leses 4-6 inches from the subjects.i set the camera to f-11 and 1/30s
  • QarikQarik Registered Users Posts: 4,959 Major grins
    edited June 6, 2011
    as explained above, it doesn't increase the zoom..it just shorten the minimum focal distance. were you tripoded and were you using a flash? If you were not tripoded and assumiong you were at 200mm, the shutter speed is very slow and maybe introducing camera shake which has nothing to do with with focus performance of the lens and tube. If you are using flash then the camera shake/shutter speed may not be much of an issue since the flash willtend to "freeze" the action. Even then your shutter speed may contrubute to some ambient exposure which may distort your apparent focus.
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  • yooperdooperyooperdooper Registered Users Posts: 231 Major grins
    edited June 8, 2011
    experiment
    i did use a tripod and not a flash
  • yooperdooperyooperdooper Registered Users Posts: 231 Major grins
    edited June 8, 2011
    today i used a flash and got good focus from both lenses
  • Brett1000Brett1000 Registered Users Posts: 819 Major grins
    edited June 11, 2011
    yooperdooper wrote: »
    today i used a flash and got good focus from both lenses

    good, if you do a lot of macro then a dedicated 1:1 macro lens is useful
  • yooperdooperyooperdooper Registered Users Posts: 231 Major grins
    edited June 12, 2011
    i only got good focus on a couple of shots using the flash-then the shots were back to out of focus.ive been using [EMAIL="f5.6&f8@1/30,iso"]f5.6&f8@1/30,iso[/EMAIL] 100.the weather has been overcast.i used an extension tube and a 200mm lens thanks john
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