I tried correcting the CA in that image using both ACR and PTLens and
wasn't having much luck. I was having to correct in both axes (I had to
rotate the image after first correcting horizontally). But even after
correcting both axes independently the result still wasn't very good.
Fortunately, I don't have much experience in correcting CA so I don't
really know what I should expect. (But I've never had to correct in two
axes by rotating the image 90 degrees).
Chuck Norcutt
C.H.Ling wrote:
> I won't put my hope to the in-camera CA correction, I don't see Olympus is
> working well here based on my DZ8mm experience. On the other hand most
> of my OM lenses are having minimum CA when stopped down 2-3 stops
> (even the F2 lenses) on 5D II, I believe 5D II don't know how to correct
> the CA of my MF lenses and they are the old lenses that do not have
> parallel rays to the sensor.
>
> C.H.Ling
>
> ----- Original Message -----
> From: "Ken Norton"
>>> It exhibits pathetic chromatic abberation, and this at f/6.3! I really
>>> hope this is not representative of that 17mm lens, thus far I am greatly
>>> unimpressed. I mean, come on, they should have AT LEAST made it an f/
>>> 2.0 lens
>>>
>>
>> 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. With
>> a
>> lens this close to the sensor surface you're going to get distortion of
>> many
>> kinds--not just CA. 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.
>>
>> Your criticisms are sound, but at the same time, I must challenge this as
>> being "Old Think". In "Old Think" the manufacturers compromised size and
>> lens-film/sensor relationship for optical precision. Now, the
>> lens-sensor-processing is considered to be an unified system.
>>
>> 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. 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. 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.
>>
>> However, this approach was a hardware solution to the problem. All
>> manufacturers determined that hardware was preferred, but would still put
>> the cameras at a distinct disadvantage as compared to equivalent film
>> cameras because of lens-size and lens-to-sensor distance. So, software
>> solutions were developed and today's processsing does a remarkable job of
>> correcting what used to be a hardware only solution. The hardware-solution
>> approach is exactly why Olympus 4/3 lenses are so huge!
>>
>> The "New Think" allows lenses to be designed more like they were designed
>> for film cameras--allowing extreme light-ray angles to hit the sensor
>> surface. Unfortunately, the sensor surface isn't flat and just the sensor.
>> There are microlenses and UV/IR filters and AA filters. As the lightray
>> approaches the edges of the sensor, the more distorted the lightray
>> becomes
>> as it has to pass through these materials of increasing thickness.
>>
>> 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).
>> Unfortunately, modifying the microlenses still affects color artifacts as
>> well as vignetting so the in-camera processing is programmed to
>> automatically correct for this.
>>
>> "New Think" means that since "perfection" is achieved through software,
>> that
>> it frees the lens designers from the constraints of size and distance.
>> They
>> can now make the lenses tiny. In essence, it's now marketing driving the
>> show and saying how large the lens can be and how thick it can be.
>> Obviously
>> there are going to be issues. No matter how you slice it, a 17mm lens is
>> difficult to make in any format. Had they designed it for optical
>> performance, the lens would be comparable in size to an old Zuiko 24/2.8.
>>
>> AG
>
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