On 4/5/2010 8:16 AM, Ken Norton wrote:
> (I know, bad subject line...)
>
> Sooo, I'm trying out my new lens, a lovely (even though it's black-nosed)
> Zuiko 50 F1.4 lens--greater than 1,100,000 serial numbered jobby.
>
> I'm curious so I try to see if the aperture wide-open is truly F1.4. Well,
> not so sure. (to be fair, I've always questioned the accuracy of wide-open
> apertures with many lenses, so bear with me).
>
I've often thought that much of the endless discussions in film days
about proper exposure indices and so on were mostly driven by
inaccuracies in and differences between different peoples equipment.
Every step of the way, there are manufacturing tolerances. Mostly, they
cancel each other out, but in some systems, they are additive.
> Using three different cameras
Inadequate info to theorize much. May I assume that on the OM bodies,
the physical aperture stayed wide open as you twiddled the ring, while
on the E-1, the physical aperture changed?
If so, all you are measuring on the OMs is the linearity of the internal
mechanical linkages within the lens, between lens and camera and within
the camera body that together simulate the effect of closing down the
aperture while actually keeping it open for focusing. So on the OM
bodies, the change in indicated shutter speed is simply a factor of how
far the little tab on the back of the lens moves and how the body
interpretates that movement, as there is no change in the actual amount
of light hitting the meter.
So - unless you measurements were taken with the DOF button pushed, they
don't actually mean anything.
I have seen similar effects with OM lenses on OM bodies. I've idly
wondered whether they may be an intentional feature of Oly's faster
lenses to compensate for something I don't know about. The actuality is
impossible to measure without specialized equipment.
In practice, the actual physical opening when stopped down will
generally differ at least a bit from ideal in most older MF lenses. I
suspect that it may also differ between presing the DOF button and
faster, stronger actuation by the camera.
If you look at the old Pop Photo tests, such as those Brian has posted,
you will see that the actual f-stop of tested lenses often varies quite
a bit from the nominal value, partially as a result of sample variation
in actual focal length.
I've often thought that much of the endless discussions in film days
about proper exposure indices and so on were mostly driven by
inaccuracies in and differences between different peoples equipment.
Every step of the way, there are manufacturing tolerances. Mostly, they
cancel each other out, but in some systems, they are additive.
On any of the OTF bodies in auto mode, of course, inaccuracies in the
visual indication in the viewfinder aren't reflected in the actual
exposure. Unfortunately, though, we have no way of knowing the actual
shutter speed.
The E-1 is more interesting, as the physical aperture is being stopped down.
First, we need to address rounding precision effects. The E-1 can show
shutter speeds in 1/3 stops. If the actual opening for one aperture
setting is just 1/12 stop too wide and that for the next full stop is
just a tiny bit over 1/12 too small, the meter will show only 2/3 stop
difference, when it is really 5/6.
"(to be fair, I've always questioned the accuracy of wide-open apertures with
many lenses, so bear with me)"
As far as I know, none of them are accurate measures of transmitted
light. The only consumer lenses I'm aware of that are marked in T-stops
are mirror lenses. I've physically measured several and found that the
marked f-stop in all accurately reflected the loss of light from the
central mirror. So the older the coating technology and the more
elements, the more difference between marked f-stop and actual t-stop.
However, that should'nt effect the experiment you are trying, as
everything is relative to the wide open light transmission.
However, you are making another possibly unwarranted assumption - that
the metering system works properly with MF lenses. Since I don't deal
with them, I don't remember the corrections needed for OM lenses on the
E-thingies, but I do remember that they are significant, and that Oly
published a list.
I tried your experiment with OM 50/1.4 >1,100,000 on the 5D. I got some
somewhat strange and inconsistent seeming results. For example, there
was often no difference in indicated shutter speed between f1.4 and
f2.0. Peering into the lens, it was physically stopping down. Then when
I sat down to put the numbers into a spreadsheet and see if I could make
sense of them, I remembered this test I did - with the same lens -and
the 300D. <http://www.moosemystic.net/Gallery/tech/300D/300Dexp.jpg>
Hmmm.... In Auto mode, the exposure got brighter from f4 to f2, then
was almost the same at f2 and f1.4 - with the same shutter speed.
In manual mode, I got pretty even exposures across the board, but again,
the same shutter speed for both f2 and f1.4. Makes no apparent sense,
but then, the metering system expects to know the aperture of the lens.
Sooooo, I suspect that the E-1 is also not an accurate instrument for
measuring relative f-stops with MF lenses.
Don't worry, take pictures.
Moose
> , the E-1, the OM-3Ti and the OM-2S, the aperture wide-open isn't F1.4, but
> closer to F1.8.
>
Without further information, you can only say that the indicated f-stops
are inconsistent, not which, if either, is correct.
> For example, when tracking the exposures while clicking the aperture ring, I
> get nice multiples except for the last wide-open stop.
>
> F16 at 1/8
> F11 at 1/15
> F8.0 at 1/30
> F5.6 at 1/60
> F4.0 at 1/125
> F2.8 at 1/250
> F2.0 at 1/500
> F1.4 at 1/640
>
> So, my confusion comes in with the the F1.4 reading. Shouldn't it be F1.4 at
> 1/1000? Who took my .56ms?
>
> AG (not nearly as bright as my lenses) Schnozz
>
--
_________________________________________________________________
Options: http://lists.thomasclausen.net/mailman/listinfo/olympus
Archives: http://lists.thomasclausen.net/mailman/private/olympus/
Themed Olympus Photo Exhibition: http://www.tope.nl/
|
