In article
>Bob Neuman (d_ruether@hotmail.com) wrote:
>: In article <51747s$gnm@inet-nntp-gw-1.us.oracle.com>, jtjioe@us.oracle.com
>: says...
>: >What can I use for Nikon 105/2.8 AFD Micro lens to be able to focus
>: >real close? Should I use extension tube or close up filter/lens?
>: Nikon 4T achromat or Sigma achromat, tubes, and/or teleconverters
>: will all give good results alone or in combinations, if you use
>: f11-16.
>How can i calculate the tube lenght? and the effect in ther apperture?
Since the 105mm f2.8 Micro-Nikkors are not fixed FL lenses (they zoom
a bit to shorten the extension that would normally be needed for close
focus), figuring exposure loss with (or without) tubes is not straight
forward. Adding an achromat (or other close-up lens) shortens the FL,
and also makes figuring difficult. (There is a one stop loss when using a 1.4X converter, and two stop loss with a 2X, in addition to the losses
due to extension.) Unless you are using TTL flash and/or ambient light metering, you may find it easiest to bracket a set of slide exposures
of a medium grey subject (1/3rd stops, toward overexposure) for each combination and magnification of interest, keep good notes, and compare exposures of the best frames with a normal exposure metering of the same subject in the same light.
Hope This Helps