Miha,
When you double the length the light has to travel you will have a two
stop loss. This means if you add a 50mm extension tube on your 50mm
lens, you would have to open up two stops. Or, your meter reading
should go from 1/60 @ F-8 to 1/60 @ F-4.
Alan
<<Date: Thu, 28 Feb 2002 09:26:51 +0100
From: "Miha Valencic" <[EMAIL PROTECTED]>
Subject: EOS Extension tube, light loss, CONFUSED
Hi all!
We've been trough extension tubes, light loss and TTL metering already.
BUT (you knew there was a but following, didn't you) I received weird
results.
I was using EOS 300 (Rebel 2000) with EF 50 f/1.8 and EF 28-135 IS with
Kenko extension tubes (12, 20, 36 mm).
I think I can safely state that there is light loss involved when using
extension tubes. So I'll go from there.
I printed my target (18% grey) and metered of it. The light source was
neon light (so there is no variation in luminance). I used partial
metering.
Now, the confused part. Without extension tubes, I get 1/60 @ f/4.
When I put 12, 20 or 36 mm tube on it, I still get 1/60@ f/4.
Confusing.
I then switched to 28-135.
I got 1/90 @ f/4 without the tube. Notice the difference?
1/45 @ f/4 with 36 mm tube.
1/60 @ f/4 with 20 and 12 mm tube.
Maybe there are subtle variations in light reaching the sensor so the
measurements are off a bit, but I should be getting around two f stops
of light loss with 36mm tube, right? Where is it?
Gerard, you used extension tubes if I remember correctly, what's your
experience with 28-135 IS and ext. tubes?
Kindest regards,
Miha.>>
=====
Alan Siegle ([EMAIL PROTECTED])
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