RE: [OM] Extension tubes?

[Brian P. Huber]

Jerry,
By extending the lens from the camera body, focusing becomes closer and the
photograph of the object will become larger (magnification). When you attach
an extension tube, you are adding 7 or 14 or 25 or other "extension" from
the film.  This extension will allow you to focus closer, but will also
prevent focusing to infinity.
A 50mm lens needs 50mm of extension to reproduce to life size (1:1).  If you
extend the lens 25mm, you will have a 1/2 life size photo (1:2).  Guess
what, a 100mm lens needs 100mm of extension for life size (1:1).
When you use a bellows, you will get continuous extension , unlike the
extension tube stepped changes.  This allows for easier composition and
control, but a bellows also costs more and is not as portable as extension
tubes.
Another factor of tubes and bellows is that as you extend the film to lens
distance, you must also increase exposure to compensate for the falloff of
light.  There's a formula for this, but TTL takes care of it automatically.
In all cases (99% anyway) you must use a tripod or other support device.
Just like you would use a tripod for a 300mm lens.

Brian Huber
-----Original Message-----
From:   owner-olympus@xxxxxxxxxxxxxxx [mailto:owner-olympus@xxxxxxxxxxxxxxx]
On Behalf Of Jerry Stackhouse
Sent:   Tuesday, May 25, 1999 7:29 PM
To:     Olympus (E-mail)
Subject:        [OM] Extension tubes?

Can someone explain the functions of extension tubes in general and how
they relate to the OM Macro lenses &regular lenses? Where does the bellows
enter the picture? Thanks.


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