Hi all,
> From: Dawid Loubser <dawidl@xxxxxxxxxxx>
> <begin rant>
> This sample image posted by DPReview (warning: huge file) is of the E-P1
> with the new 17m lens at ISO 200 at f/6.3:
>
>
> http://a.img-dpreview.com/gallery/olympusep1_preview2/originals/p6160172.jpg
>
> It exhibits pathetic chromatic abberation, and this at f/6.3! I really
> hope this is not representative of that 17mm lens,
These are supposed to be pre-production units, so maybe it's just a bad
sample.
For example,
> take the
> (much smaller and cheaper) Voigtlander 35mm f/2.5 Skopar (for Leica M-
> Mount)
> pancake lens
Well, not much smaller... the M.Zuiko 17/2.8 measures 22 mm long by 57 mm
diameter, whereas the Skopar is the same length (without hood) by 55 mm
diameter -- seems not to deserve the 'Pancake' nick very much.
> it's faster,
Just a third of a stop...
> and renders a *much* better image, and it's an ancient design.
I don't think it's an ancient design... despite the 'classic' naming, these
Cosina-Voigtlander lenses are completely new designs -- but, IME, yes, they
do deliver superb pictures. I have no experience with the 35/2.5, but if it
were _half_ as good as my new Voigt 28/1.9, then it would be GREAT!
Also, the noise at ISO 200 is exceptionally poor
From: "C.H.Ling" <ch_photo@xxxxxxxxxxxxx>
> Not having tested the lens and camera myself I will not comment on the
> image
> quality, especially I found I usually got MUCH better result with RAW on
> Olympus images. Over sharpening is usually the cause of noise images
The Lumix G1 exhibits (according to dpreview) rather poor JPEG performance,
while kin RAW improves vastly! If we assume that quite a bit of its
underpinnings are like those on the E-P1, shooting RAW may help a lot!
> Is the 35mm f/2.5 Skopar images 100% cropped from 4000dpi scan? If not I
> don't know how to compare them.
Obviously, if it's just the web-resolution picture on your links, there's no
way to compare.
> From: Ken Norton <ken@xxxxxxxxxxx>
> I'd say that it's a little early to say for sure why, but I suspect that
> there is a bug in the processing firmware that didn't correct the CA.
<snip>
> The in-camera processing that all manufacturers are
> putting in the cameras now are automatically repairing CA, color-fringing
> and vignetting before the RAW file is written. I suspect that this is just
> a
> case where the calibration of the processing is off and will probably be
> fixed in firmware version 1.1.
Maybe -- although I'm from the "old think" school, and I don't picture (pun
intended) well these things...
> To make the 17/2.8 that small and that close to the sensor means that the
> light-rays is no longer perpindicular to the sensor surface but approaching
> the surface at extreme angles.
Well, not THAT close... remember everything is scaled down, so the
flange-to-sensor distance of 20mm would be equivalent to 40mm on a full
frame camera; no much less than, for instance, Can*n FD (42mm) or Konica or
Minolta -- and only 13% less than our beloved OM's!
And despite the lack of a mirror, the optical elements on this controversial
lens don't protrude deeply into the body... see <
http://www.olympus.es/consumer/images/MFT_E_LensDiagram_17mm.jpg> where we
can deduct two things:
–The rear element is located very near the mount plane, so the most
"extreme" angle light-rays will reach the sensor is about 29º... that is
arctan(11/20) -- isn't 22mm (11x2) the image circle diameter in 4/3?
–It ain't (a regular) double-Gauss... it's a f****** retrofocus!!! See the
STRONG negative element at front :-(
Do you remember how Olympus made a big deal
> about how the 4/3 lenses were specifically designed for digital by making
> the light rays as parallel as possible when leaving the rear element.
Yes, the "telecentric" design. This is far from new; my old Russian book on
Optical Instrumentation already defines it:
"Fig. 6.2a shows a stop placed in the first focal plane, consequently the
principal ray will be parallel to the optical axis in image space. When the
stop is at one of the principal foci, it is said to be a _telecentric stop_
[...] Ray pencils are referred to as _telecentric_ if their principal rays
travel parallel to the optical axis either in object or image space.
Telecentric ray bundles in image space are used in photographic objectives
(often referred to as photographic lenses) operating with colour
multiple-layer film, and in TV objectives with the sensitive layer of the
photocatode having a considerable thickness"
If
> you can make the light rays approach the sensor direct-on instead of at
> extreme angles, there is no need for color and vignetting correction.
>
But even with film (which doesn't care the incidence angle) any lens may
have light fall-off/vignetting and colour aberrations.
The hardware-solution
> approach is exactly why Olympus 4/3 lenses are so huge!
>
From: Moose <olymoose@xxxxxxxxx>
In the case at hand, as you say in your detail, the problem is the
> sensor. If the sensor requires relatively parallel rays striking it,
> then the lens design becomes more complex, probably relatively large,
> heavy and retrofocus
The basic solution for a telecentric lens, as explained in my Russian book,
would be placing the stop (aka. diaphragm) at the front focal plane -- I'm
no optical engineer, so there may be many other optical tricks out there,
but that seems more feasible with a retrofocus design, which already has "a
lot of things" at the front... this may explain the size of Oly's 4/3
lenses.
From: Ken Norton <ken@xxxxxxxxxxx>
> What Olympus/Panasonic did to help resolve this problem is to remove or
> degrade the AA filter and modify the microlenses. (Kodak removed the AA
> filter nearly entirely from most medium-format and M8 sensors).
Not necessarily a bad move, IMHO.
No matter how you slice it, a 17mm lens is
> difficult to make in any format.
> From: Moose <olymoose@xxxxxxxxx>
> I'm with Wayne on this one. Making a 17mm lens for 4/3 size film would
> be pretty straightforward, a nice little D-G would do, and much simpler
> than making a retrofocus 24/2.8 for FF film.
>From: Dawid Loubser <dawidl@xxxxxxxxxxx>
>And it is difficult to design a 17mm lens for 35mm, yes, but for 4/3
>you could do an exact
>scaled-down (half-size) version of a great 35mm design for 35mm, and
>you arrive at the "same" end result.
I agree. In fact, for a f/2.8 lens, I don't see the need for the D-G scheme:
a Sonnar, for instance, would suffice; or even a Tessar -- the Minox has it
in the same 35mm f/2.8 configuration.
But they had to make it retrofocus... :-(
From: Ken Norton <ken@xxxxxxxxxxx>
> Had they designed it for optical
> performance, the lens would be comparable in size to an old Zuiko 24/2.8.
>
Can't tell for sure. However, at 31mm length, it isn't much bigger.
What I can assure is that a Tessar 45/2.8 (OK, OK, it's only 50º in FF
instead of 65º) which is only 18 mm long and weigths 90 gr, does perform
great on digital sensors: <
http://galactinus.net/vilva/retro/eos350d_tessar45.html> (sorry, I don't
have at hand my Señorita-samples with this lens ;-)
From: Dawid Loubser <dawidl@xxxxxxxxxxx>
> Ken, I have to disagree. If the extreme CA I am seeing here (and this
> is extreme - it's
> been a long time since I've seen such consistent CA across the image)
Do my eyes deceive me, or I'm seen much less CA at the bottom left?
> would only be prominent in the outer zones of the image, and not
> towards the centre of
> the image where the rays are indeed quite perpendicular to the sensor
> surface.
Maybe it's just decentering, like my Can*n 18-55 plastic kit lens... that
means just poor manufacturing quality, which may be reasonable on a
pre-production lens.
> All your arguments make the lens worse in my opinion, e.g. by bringing
the lens closer
> to the sensor surface, you are freed from all of the problems of doing
> a retrofocus
> design, you can employ a true symmetrical / wide angle design.
Unfortunately, this is not the case.
> here is a 100% crop shot on a 2004-vintage DSLR in harsh daylight
using their cheapest 35mm f/2.0
> (retrofocus, much harder to design, and much faster aperture, designed
> for film) lens
I assume it's on EF mount... should it share the same optics of the later
FDn 35/2 (rather lightweight with a diminutive front element) then it's a
GREAT performer...
> From: "Wayne Harridge" <wayneharridge@xxxxxxxxxxxxxxx>
> Interesting, in this interview he says "If customers request a prime lens
> the most, then it will be the first one to be made.".
>
> I wonder how one requests a particular feature from Olympus ?
>
So do I!
Cheers,
--
Carlos J. Santisteban Salinas
IES Turaniana (Roquetas de Mar, Almeria)
<http://cjss.sytes.net/>
--
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