> -----Original Message----- > From: [EMAIL PROTECTED] [mailto:owner-eos@;a1.nl]On Behalf Of Keith Green > Sent: Saturday, October 26, 2002 1:54 AM > To: [EMAIL PROTECTED] > Subject: Re: EOS Missing EXif info > > > Chip Louie wrote: > > > > Craig Zendel wrote: > > > > Anyone know why my 50mm f/1.4 does not record the focusing distance in > > > D60. > > > Could it be due to the fact that the USM motor in the EF 50 > 1.4USM is not > > a ring type USM but a micro-USM and cannot give this type of positional > > data? > > I was just guessing as to why this seems to not work. The > "fact" part was > > related to the EF 50 1.4USM having a micro USM AF motor, not a ring type > > USM. I'd also venture a guess that most of the older non ring > USM lenses > > fail to give this information and that even the older ring USM lenses > > without internal or rear focusing groups work the same. But I > don't know > > as I have not been able to use an EOS D60 yet and even if I did have > > access to one I don't have any of the older non USM or USM > lenses without > > IF or RF groups to test it with. I'm sure that someone here > will fill us > > in as time goes by. > > > <Clipped> > > > > My thinking was given that a ring USM is made up of relatively large > > circular structure surrounding the focusing group cam tube they would > > offer a convenient location to put positional encoders with a very high > > level of resolution. A micro-USM motor cannot offer this same large > > diameter structure to work from and would offer much less accurate > > positional information without a more complex mechanical and electronic > > arrangement for a positional encoder. I suppose they could > have put them > > on the cam tube of the focusing group of the EF 50 1.4USM but this seems > > less convenient than simply using a ring USM's structure and electrical > > conduits for signal transmission for the encoder. > > Perhaps this is why Canon does not use distance information for flash > exposure calculation. > > Cheers > > Keith >
Hi Keith, Very good point and something I always wondered about. Distance to subject would seem to be a more reliable guide for flash exposure than trying to evaluate flash exposure during the exposure without knowing the distance. The problem with TTL or even A-TTL on EOS cameras is that there is no direct looking sensor for flash exposure evaluation, the sensors look at reflected light from the film. Film varies and much like using reflected light meters for exposure are thrown off sometimes. Cheers/Chip * **** ******* *********************************************************** * For list instructions, including unsubscribe, see: * http://www.a1.nl/phomepag/markerink/eos_list.htm ***********************************************************
