On 11/9/2012 7:20 PM, Jim Couch wrote:
> Yeah, I think it helps one to make better decisions regarding when and
> when not to use IS.
And yet ... His "The first and most important rule of VR is this: never turn VR
on unless it's actually needed." is
based on:
"... VR is essentially a element group in the lens that is moved to compensate
for any detected camera motion. Because
this element group is usually deep in the middle of the lens, usually near the
aperture opening but not exactly at the
opening, you have to think about what is happening to the optical path when VR
is active. Are there times when it shifts
where it imparts a change to the image quality other than pure stabilization? I
believe there are, though the impact is
visually subtle. Some of the mid-range distance bokeh of certain VR lenses
appears to be impacted by VR being on. Put
another way, the background in the scene is slightly moving differently than
the focus point in the optical path. This
results in what I call "busy bokeh," or bokeh that doesn't have that simple
shape and regularity we expect out of the
highest quality glass. "*
*
None of this applies at all to in-body IS.
It's impossible to know about sampling frequency without knowing what it is on
various IS systems. Most of the rest
either doesn't apply, we already know or is common sense.
As I mentioned, I forgot to turn off IS when comparing Z.D 12-50 in Macro Mode
vs. OM 50/2 Macro. Here's an image fro
the 12-50 with 100% samples, center and edge.
<http://www.moosemystic.net/Gallery/tech/E-M5/IS_On_Tripod/_9302316.htm>
Lots of fine detail in sharp focus in the center. I don't see anything I would
think is motion blur
By sheer happenstance, one petal extending to the edge and almost the corner
remained close to the focal plane. It isn't
quite as sharp as the center, but impossible to tell how much of that's due to
lens and how much to DOF. That's what
flat test charts are for.
In any case, there are tiny highlights in that section that don't seem to show
any motion blur.
My conclusion? Forgetting to turn off E-M5 IS on a tripod isn't such a bad
thing. The E-M5, six axis IS system is quite
different from both 4/3 and preceding µ4/3 cameras, so I don't believe my
result is generalizable.
As to turning it off for higher shutter speeds, I don't know. I would have a
problem with that in the field. One of my
lenses goes out to 600 mm eq., which I use not infrequently. That requires
1/600 without IS, more, really, with the
ability to pixel peep if one might crop or print large.
I seem to be finding that relying on the old 1/shutter speed rule is giving me
sharper results, with IS on, than relying
on the IS to give me a couple of extra stops. Extra long simply puts more
strain on IS? Running past the sampling
frequency? Too small a sample as yet? I dunno.
BTW, about the only thing I conclude from this informal test is that there
isn't any difference worth thinking about
between the two lenses at this magnification.
Testy Moose
--
What if the Hokey Pokey *IS* what it's all about?
--
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