Henning, Now here I agree with you. The build is more like a consumer lens, but it is optically superior to other wides. BTW, I did some checking and what you say about extension tubes on fast lenses may be true. One reason why in some Zeiss lenses they have floating elements, but the 135mm F2 is another story. I think this is due to something called the optical invariant or Abbe's optical invariant and not well covered in texts. Also, a lens with fixed elements (most of them) can be corrected completely for spherical aberration and coma at only one distance. At other distances some aberration is increased. Normally, camera lenses are designed to be optimum at about infinity and maintain corrections well down to about ten focal lengths. For this reason camera lenses generally are not ideal for close up work or for enlarging although a relatively slow, normal angle, lens will do OK. Perhaps I will stick with macro lens for macro work. BTW, you would not believe how good the Sigma 70mm is. If you get a chance to try one check it out. Its just bad at F2.8, but at smaller apertures, especially F8, and F11/16, wow!!!! Peter K
Hi Peter,
I have checked out the Sigma, since macro is an interest of mine. All of the Sigmas have been decent, including the 70 which is one of their better ones, but the two samples I tried didn't do nearly as well as the 60 EF-S. I do like the 180, though. The 150 was appealing, but I only tried one sample and it wasn't really good. With Sigmas variable QC, that might have been a dud. They have a lot of good optical designs, but I wouldn't ever buy a Sigma without being able to exchange it or try a number of samples.
The thing with the extension tube thing is that since non-IF lenses have to be corrected over a wider reproduction range than IF lenses, other compromises are made to allow this, but then going a bit further out of their optimum reproduction range doesn't upset their correction as much as IF lenses, which in normal use don't have to make any allowances for different reproduction ratios due to movement of the whole lens assembly.
-- * Henning J. Wulff /|\ Wulff Photography & Design /###\ mailto:[EMAIL PROTECTED] |[ ]| http://www.archiphoto.com * **** ******* *********************************************************** * For list instructions, including unsubscribe, see: * http://www.a1.nl/phomepag/markerink/eos_list.htm ***********************************************************
