CN writes
>> Micro 4/3
>>> focal length of about 34-190mm
AG:
>>2. ANY gain is going to be substantial. Having my 28mm lens not act
>>like a 58mm lens, but more like a 35mm lens will make me very happy.
Hmmm, some interest in this gizmo here.
Brian Caldwell clarified some stuff about this adapter on another site:
MFT version NOT just change in mounts:
brianc1959, on 16 January 2013 - 06:07 , said:
"The micro-4/3 version will use a different optical design than the NEX
version, although the magnification will be the same at 0.71x. Because
of the smaller format I was able to get really good center-to-edge
performance, as shown in the MTF section of the white paper."
Question: "would have thought the m4/3 image, being smaller, would
covered the "sweet spot" of the NEX image, so there would be no need
for different optics? But you are the optical expert, not me :)
BC answers:
"There were actually several reasons we opted for different optics on
the m4/3 version. The first one was that m4/3 cameras present
different mechanical obstacles near the sensor coverglass, and the NEX
version simply wouldn't fit. Second - and more importantly - by
optimizing for the smaller sensor I was able to get better performance.
You can see this in the MTF curves published in the white paper. "
>From page 5 of the speed booster white paper:
"Speed Booster has a very small amount of undercorrected spherical
aberration at f/0.90, but this was done intentionally to improve the
bokeh when the Speed Booster is used with ultra high speed f/1.2
objectives."
rvink comments:
I assume at smaller apertures, spherical aberrations are more or less
perfect corrected, so that bokeh should be largely unchanged from the
master lens.
I wonder what effect the speed booster has on contrast, flare and
ghosting? Adding 4 extra elements is bound to cause some issues.
Brian replies,
The amount of spherical undercorrection is very slight, and is gone by
the time you stop down to f/1.0. As can be seen from the MTF curves for
the 50/1.2 Nikkor its not enough added aberration to prevent the Speed
Booster from dramatically increasing the on-axis MTF when the combined
system is used wide-open at f/0.90.
In practice the dropoff in sensor sensitivity with incidence angle will
have a much bigger impact on bokeh than the tiny amount of spherical
aberration present in the Speed Booster. I call this effect
"sensor-induced apodization", since it acts just like a graduated
neutral density filter placed at the aperture stop. BTW, Minolta used
exactly this sort of ND filter in a 135mm portrait lens they developed
some years ago. In any case, the effect is that the outer parts of
defocused highlights become dimmer than the center, which is exactly
what you want.
"The coatings on the four elements have better than 99.5% efficiency,
so the total transmission loss due to the Speed Booster is less than
4%. For comparison, this is half the amount of loss you get from an
uncoated filter, which will reflect 4% per surface. In our tests we
haven't been able to detect any flare difference with and without the
SB. One reviewer has reported a small amount of flare to us in a shot
he took in harsh lighting conditions, but we have been unable to
reproduce this result and are still investigating whether this was due
to the SB or to the objective he used."
Have only seen a very few images compared to same lens on FF with NEX
--looks interesting thus far.
Unfortunately no AF with Bo Ming converted Contax N lenses--bah.
Rather slow AF thus far anyway it appears.
Paying attention, Mike
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