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

On 7 Sep 2006 08:48:06 -0700, Bill Hilton wrote:

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:

Ah, that's the post I was thinking of ... thanks for digging that up
... which lens was he using, the 500 f/4 (which is what I think I
remember) or something else?

Good memory. :) Here's more from the message. I didn't save the
original (which was from eawckyegcy@xxxxxxxxx), so what I have is
taken from quotes in one of Roger's messages.

The lens was an EF 500/4, but others (EF 20/2.8, EF 300/4) didn't
change much. Note the relatively low impact of using IS, and the
large impact of the AFing (the lens was racking from close to
infinity). Also note the low image write current.

Peak current of 1.15A was measured during a 9 "raw" frame pipeline
fill/drain episode. This peak was unaffected by IS or AF, suggesting
that it is still an underestimate (unlikely given the Fluke meter I
was using), or that AF (the larger of the two) is briefly disabled
during mirro flip, shutter open, etc. Note that the act of taking a
picture should demand a fair amount of energy given how fast these
moving parts are moving.

===================================================

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%.

I think the 'typical' way people use these is with IS and AF both on so
from this measurement IS adds another 7 mA or 1% ... that sounds about
right to me based on how little effect I seem to have with my battery
life. The two big power burners are just having it on for the displays
and internal electronics and running AF, from his data.

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 low number makes sense to me, though I admit I'm surprised it's
*this* low ...

It would be easy to measure and compare (base + AF) vs. (base + AF
+ IS) if all three measurements were steady, unvarying over time.
The AF current, if you could see it displayed on a scope would be
pretty ragged, and the amount of current consumed for two different
measurements would be *very* difficult to duplicate, since the
camera controls the current being fed to the motors by what it
"sees" and what is being measured is only the peak value. That's
why I can't automatically accept the 665ma and 672ma values, because
if done again, the tests might produce 648 and 697 (49ma) or even
678 and 671 (minus 7ma). The latter would seem to indicate that
using IS helps to recharge instead of delete the battery ( <g> )
when actually it's just what you'd expect from time to time when
sampling fluctuating voltages and currents.


But depending on how
IS and AF are used, IS can use more battery energy than AF.

I disagree :) At least based on the available measurements and actual
usage in the field.

I didn't say that IS would always use more battery energy than AF.
It would depend on how the camera was used. The more rapidly you
take pictures the greater the effect of the AF's power consumption.
Taking shots rapidly may very well be typical of the way you take
shots in the field (when the camera is no longer hibernating). An
extreme opposite example would be someone wandering around with the
camera ready to shoot, set for continuous IS, but not continuous AF,
the AF only occurring when the shutter is at least partially
depressed. If only one or two shots are attempted per hour, the AF
system won't use much power at all compared to the camera's other
subsystems. But the IS would be chugging along non-stop, and
whether it's only 7ma or 15ma, it'll still add up. Not to the point
that you'd think you were getting shorter battery life. Just that
it's possible for the IS to use more energy that the AF in some
cases, and they don't have to be as extreme as the example shown
here. It just requires a thrifty photographer that thinks he/she's
still shooting film. :)


So more than a 2:1 difference between the min (920) and max (1,838) ...
the lower ones were all in colder weather, either Bosque at sunrise
when it's near 0 F or Alaska (Pribilofs and Katmai) where it's probably
40-55 F ... at least one of these (Pribilofs) was with the 400 f/5.6 L
which doesn't have IS at all ... the one with 1,838 was in Tanzania
where it was very warm and also where I shot about 3x as many in one
day as I usually do. Every single one of these 1,838 was shot with the
500 f/4 L IS with IS on. I can rationalize this high number of frames
because a lot of the power (more than half) is wasted in Idle mode with
the displays etc so shooting a lot in a short time means the % time
spent in a non-shooting but power burning mode is minimal. At least
that makes sense to me.

So from this I think the number one factor is probably the temperature
and number two is probably how long is spent between shots (where power
is wasted by the display etc). IS just doesn't register as a factor,
the way I see it.

Temperature is an important factor in determining how many shots
you'll get per charge, but it's no more significant than if you used
a battery of 1/2 the capacity or a 3 pound external monster. At
least for what I was discussing, which was the relative amounts of
energy used by the IS and AF systems. I have no way to test it, but
I think if you were restricted using standard Canon parts and to
loading the camera up with batteries only once, when the temperature
is extremely low you might get by far the longest life from filling
a battery grip with lithium AA batteries. That temperature might be
way too low for the photographer, though. :)

.

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