In article <533akr$181@kannews.ca.newbridge.com>, dchan@Newbridge.COM says...

>I have the following Nikkor MF Ais lenses and I like
>to take pictures of flowers and bugs with higher
>magnification.
>105 f2.8 Marco, 135 f2.8, 200 f4.0.
>I would like recommendations and explanations of
>which Nikon extension tubes I should buy?
>Any other accessories I should consider?

Tubes will disappoint you with the 135mm f2.8.
The PN-11 (2") tube will be the most useful
single tube with the other two lenses. The Sigma
achromat sold with the 90mm macro lens (available
from Sigma for about $35) is really excellent on
the 200mm f4 (non-macro) when it is on tubes or
converters for high magnification (sharp at 3X
at f11-16), and should give good results at
f11-16 on the other two lenses. Converters are
useful for macro work, too, though to be able
to use small stops, you may want to mount a TTL
flash at the end of the lens, pointed at the
subject (since the light source size is relatively
large compared with the subject size, the flash
light is very soft and natural-looking).
Hope This Helps