Re: EF 28-80mm f/2.8L IS USM... when?

On 6 Sep 2006 18:30:30 -0700, Bill Hilton wrote:

Several f/2.8 L lenses already have IS, including heavy-weights like
the 300 f/2.8 and 70-200 f/2.8, which kind of shoots this theory down.

Well, I said it was a complete guess, and was based on an
erroneous claim that a large f/2.8 IS wasn't offered by Canon. I
wouldn't shoot down the theory so quickly though. It explains why
Canon hasn't produced any 70-300 f/1.4 L IS lenses. Among other
reasons of course. <g>


I use a 500 f/4 L IS and 70-200 f/2.8 L IS a lot with IS on almost all
the time and even the 500 doesn't seem to noticeably cut down the
battery life for the 1D M II batteries. I keep track of how many shots
I get with each battery (so I can tell when to recondition them) and
there's very little difference in total shot counts.

A couple of years ago someone hooked up a meter and measured the
current for different modes and I think AF took about half the total
current but IS was only taking a few percent, less than 5% IIRC. I
think he was testing a 500 f/4 L IS.

I looked in the rpd archive and found the discussion between you,
Roger and a few others back in Nov. 2004 that included the meter
measurements. Here's some of it:

Here are some current measurements of a Canon 10D. The power
supply was a single, full-charge, 3rd party BP-511, 8.2V. Various
operations:

off 0mA (probably something in the microamp area)

idle 98mA

active 406mA (shutter half-press; exposuring ongoing)
388mA (no shutter button contact)
421mA IS only \
672mA IS + AF > shutter half-pressed
665mA AF only /

AF measurements are "peak".

If I'm reading this correctly, the current used by IS can be shown
to be either 15ma (421ma -406ma) or 7ma (672ma -665ma), which
amounts to about 3.6% or 1.0%. That's close to the 5% you recalled,
since I'm suspicious about the 1.0% number and think it should be
ignored unless the test is redone using a better methodology. The
AF current is probably full of transients and I'd guess that "peak"
measurements would be highly variable if repeated several times.

So the current used by IS is probably too low for it to cause
problems when adding IS to a long, fast lens. But depending on how
IS and AF are used, IS can use more battery energy than AF. I'd
guess that continuous IS is used much more frequently than
continuous AF, so while the 15ma IS current is much lower than the
259ma AF current (665ma - 406ma), IS could use much more current for
these reasons. The 259ma value is based on peak measurements, and
the average or rms value might be much lower. To simplify
calculations, let's assume that it is equivalent to a steady 150ma.
Also, if AF is not continuous, the lens (unless it has problems and
is forced to hunt) won't consume 259ma for more than a fraction of a
second. I don't know how quickly your 1DS/lens focuses, so I'll
just guess (again) that it's about 1/2 second or less. At 15ma,
when IS is on continuously, it would only have to be on for 5
seconds to use approx. the same energy used by the AF system.
Discounting shooting continuous sequences of shots, most people
should go more than 5 seconds between shots, since at that rate
they'd take over 700 shots per hour. But as usual, YYMV.

BTW, you didn't change your IS preference, did you? Back in 2004
you said that you keep it turned off, but it was said while talking
about shooting birds in flight, so I assume that it's an exception
you made when shooting birds, and you keep IS turned on otherwise.

.

Relevant Pages

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