Manual Extension Tubes:
1. Are less expensive than the Auto Tubes
2. #1 is because they do not have the mechanical linkage to automatically
stop the lens down to its aperture setting, nor do they have the mechanical
linkage to bias the meter when turning the aperture ring. Thus, the TTL
metering measures actual light coming through the lens and tube, not the
lens wide open and the meter biased for the aperture setting as it does
with an Auto lens or Auto tube.
3. In use, because of #2, one focuses with the lens wide open, then stops
the lens down to a proper exposure aperture, then trips the shutter. If
using a body like the OM-1[n], you might have to wait a little for the
meter to adjust to the changing light. This is due to the type of meter
cell in the OM-1[n] and its Manual mode only for setting exposure. This is
similar to using the 35mm f/2.8 or 24mm f/3.5 PC Shift lenses which are
manual stop-down (the shift lenses have a stop-down button). (Is this true
for the OM-2[n] meter if used in Manual Mode also?)
Auto Extension Tubes:
1. Are more expensive than (Manual) Extension Tubes.
2. #1 is true because they have the auto stop-down and meter biasing
linkage just as the Auto lenses do, to connect these linkages through the
tube to the camera body.
3. In use, because of #2, you use them just as you would an Auto lens
alone. The TTL metering does not need any compensation for the loss of
light due to an extension as it sets the baseline wide open and bias from
there. Thus, the Auto Extension Tubes are faster, more convenient, and
less prone to exposure error (forgetting to stop down after focusing) in use.
-- John
At 15:33 1/4/01, Hefin asked:
Hi all,
What's the difference between manual and auto extension tubes, and what are
the benefits ???
Cheers, Hefin.
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