03-04-2011, 09:42 AM
[quote name='genotypewriter' timestamp='1298941874' post='6409']
Thanks for the link... right after I put my question in to words, it occurred to me that any AF varifocal zoom lens can be made a parfocal lens if the lens (or the body) can read the focal length in real-time and then automatically adjust the focus to the last manually set focal distance. In the case of lenses with a built-in AF motor, the lens itself can do this without needing the body to do anything but just providing power.
In the past I'm sure this was done using additional elements. But still what I said could be mechanically (i.e. not electronically) implemented if the focus variation when zooming is linear or something... maybe.
GTW
[/quote]
Actually, if AF is adjusted by th ecamera continually, it si technically not a parfocallens.
A parfocal lens keeps focus all by itself when zooming, no further intervention or transmission of data required, i.e., it is mechanical rather than electronic/electrical.
Yes, in the past this has been done with additional elements, but is also a matter of very tight tolerances and very complex moving mechanisms. Actually, normally it is a combination of the two, which is quite logical <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/biggrin.gif' class='bbc_emoticon' alt='
' />.
Kind regards, Wim
Thanks for the link... right after I put my question in to words, it occurred to me that any AF varifocal zoom lens can be made a parfocal lens if the lens (or the body) can read the focal length in real-time and then automatically adjust the focus to the last manually set focal distance. In the case of lenses with a built-in AF motor, the lens itself can do this without needing the body to do anything but just providing power.
In the past I'm sure this was done using additional elements. But still what I said could be mechanically (i.e. not electronically) implemented if the focus variation when zooming is linear or something... maybe.
GTW
[/quote]
Actually, if AF is adjusted by th ecamera continually, it si technically not a parfocallens.
A parfocal lens keeps focus all by itself when zooming, no further intervention or transmission of data required, i.e., it is mechanical rather than electronic/electrical.
Yes, in the past this has been done with additional elements, but is also a matter of very tight tolerances and very complex moving mechanisms. Actually, normally it is a combination of the two, which is quite logical <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/biggrin.gif' class='bbc_emoticon' alt='
' />.Kind regards, Wim
Gear: Canon EOS R with 3 primes and 2 zooms, 4 EF-R adapters, Canon EOS 5 (analog), 9 Canon EF primes, a lone Canon EF zoom, 2 extenders, 2 converters, tubes; Olympus OM-D 1 Mk II & Pen F with 12 primes, 6 zooms, and 3 Metabones EF-MFT adapters ....