Hi Julian Last year I did some measurements on macro lenses, which I'm quoting below: -----------------------------------------------------------------------------
I've just measured the various distances with my original non-USM EF 100 f2.8 macro which also has internal focusing, but which I understand has a different construction to the USM version. At 1:1, lens length front to back 15.2cm; lens front-subject 11cm; lens hood-subject 7cm; film plane-subject 31cm At 1:2, lens length front to back 13.0cm; lens front-subject 20.5cm; lens-hood-subject 16.5cm; film plane-subject 38cm. As an afterthought I've dug out my X-700 with my Vivitar 90 f2.8 macro and done the same measurements: At 1:1, lens length front to back 17.8cm; lens front-subject 13cm; film plane-subject 36cm; At 1:2, lens length front to back 13.5cm; lens-front-subject 22cm film plane-subject 40cm The Vivitar lens isn't an IF lens so keeps its 90mm focal length throughout, and its front element isn't so deeply recessed as the Canon. ---------------------------------------------------------------------- Interesting to see that the Vivitar (old-fashioned non IF type lens) returns a 1:1 film to object distance of 4x its marked focal length (as per simple text books, despite the optical cell having non-trivial depth), whilst the Canon non-USM EF100 measures out at 31cm, suggesting that at 1:1 it is something like a 77.5mm focal length. However, useful working distance at 1:1 becomes something of a joke when you put the dedicated Canon lens hood on the EF 100 f2.8 USM version, which I now have. (I've got rid of the non USM version which had a deeply hooded front element.) Incidentally on my EOS3 the EF 100 f2.8 macro USM focuses very quickly when it's away from the macro range - much faster than my 85 f1.8 USM which is a much older design. Malcolm Milton Keynes, UK ----- Original Message ----- From: Julian Loke <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Sent: Friday, November 08, 2002 12:00 AM Subject: Re: EOS Seeking macro information > But the whole point is that the REAL working distances are different from > the calculated values. What is more is the EFFECTIVE focal length at 1:1 is > half of the working distance. > > So, for a 100mm macro lens, working distance, should be 200mm, but it is > not. Hence, actual focal length at 1:1 for my EF 100mm f/2.8 USM Macro has > to be 74.5mm snip * **** ******* *********************************************************** * For list instructions, including unsubscribe, see: * http://www.a1.nl/phomepag/markerink/eos_list.htm ***********************************************************
