70-200mm f/2.8L IS @ 100mm vs. 100mm f/2.8?!?!

[JJD.Photography]

I am curious to what the difference is between the 70-200mm f/2.8L IS at 100mm f/2.8 and the 100mm f/2.8 lens. Does the 100mm just allow you to get closer for more detail of the subject?

I have read the 100mm works very well as a portrait lens. The 70-200mm also works very well as a portrait lens, but lacks detail when trying to get in close for macro work.

I also have the kenko extension tubes that I have been using on my 50mm f/1.8 How is this setup compared to the 100mm f/2.8 w/o tubes? Working distance with the 50mm + tubes blows as well for insects.

Thanks for any info.

[LordV]

Yes macro lenses let you focus much closer than normal lenses most achieving 1:1 magnification at minmum focus (ie 1cm of subject gives 1 cm of image on the sensor).

A 50mm lens with a full set of tubes can give just over this magnification level and can give excellent results with the two cons of rather close focus distance (about 2" in front of the lens) and loss of infinity focus.

A 100mm macro lens has a mimimum focus point about 5" in front of the lens, obvuiously can still focus on infinity and has a flatter focus field.

Brian V.