On Wed, Jun 14, 2000 at 11:52:36AM -0700, Lex Jenkins wrote:
> Me:
>
> Ahh, interesting. I've been puzzled about what's appropriate when using
> other-than-macro lenses with various close up devices (close up diopter
> lenses, extension tubes, Vivitar's macro focusing 2x teleconverter). For
> example, is it considered best to leave a normal lens focused at infinity
> for best results and move the camera or subject to within focus range? Or
> is it okay to use the lens' focus mechanism to get maximum magnification
> when combined with diopters, extension tubes, etc.? I've never read a
> definitive answer on this. My own informal tests of 2D objects doesn't
> reveal any particular difference, but I may be less critical than some.
When the lens has no Floating Elements there is no difference weather you use
it at infinity or close focused with extention. Floating-Element Lenses sould
be used
with lens focus mechanism set to minimum distance. But I guess this influence
is only
significant when you use the lens wide open - What you usually don`t do in
Macro work.
> That reminds me ... with a lens like Vivitar's old 90mm f/2.8 macro (the
> non-Series 1 version) that goes 1:1 without an extension tube - does this
> type of design inherently involve either a loss of effective focal length,
> effective aperture, or both as it's extended to maximum magnification?
> Again, I haven't been able to find a definitive answer anywhere.
Easy to find out. For 1:1 magnification a lens mus be elongated for it`s focal
length.
Take a ruler and meassure the lenght of the lens when focused to
1:1-magnification,
and subtract the lenght when focused to infinity. If it matches the focal
length, it
loses 2-f-Stops. If it is the same (IF-lens), it loses half of effective focal
lengh. If it is
in between, It losses an (smaller) amount of both.
Frieder Faig
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