jlind@xxxxxxxxxxx writes:
<< Close-up lenses screwed onto the filter ring will not change exposure
settings, but an extension tube will! There are tables that show the
exposure adjustment required if you ever use tubes on a *non-TTL* metered
camera. However, TTL metering compensates for it just as it does for
filters. Just remember with an extension tube on you do lose some light,
the longer the tube, the more light lost.
>>
A more subtle fact not mentioned by John is that many 35mm SLR lenses are
very
assymetrical designs (retofocus etc),this results in much greater light drop
off than the tables
would suggest, because the rear element is too small for macro use. Thus an
advantage of
macro lenses is that they have much lower light drop off as they are racked
out to
high magnifications. Lenses from rangefinder cameras which are often more
symmetrical
are probably better for macro use. I would guess using reversing adapters may
help reduce
light drop off when standard lenses are used for macro, as the rear element
is then large.
Tim Hughes
Hi100@xxxxxxx
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