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preview: Olympus M.Zuiko 17mm f/1.8
#11
Well, these auto corrections are a borderline thing from a testing perspective. The MTFs are better without. 

The Oly 17mm f/1.8 has a raw distortion of 4.5%. As a consequence there is simply quite a bit of stretching and interpolation going on in the border region. 

Since this is enforced in MFT land, it is hard to get around this.

 

Interestingly CaptureOne 7 provides the uncorrected image from RAW now. 

It is probably hard to tune this but I could try to provided the RAW MTFs besides the 'corrected' MTFs.

Not sure in how far this is helpful though.

 

The results aren't bad for the 17/1.8 but they stay way short of the 75/1.8, of course (which doesn't need any auto-correction).

#12
I really don't understand why micro 4/3 lenses are being designed with such high distortion. Contax (zeiss) lenses seemed to have decent enough resolution with almost no distortion on FF cameras (ok the 21 had massive wavy distortion; but the 25 was virtually without distortion and the 28 was pretty darn good too). Does it really cost that much to design a better lens or did these older lenses use special glass (such as lead) that are no longer allowed ?

#13
I remember from some lens maker company interview:

CA correction=bigger costs (special glass itself, strict tolerances required for such glass)

Distortion correction=bigger size or lower optical quality

#14
Quote:Well, these auto corrections are a borderline thing from a testing perspective. The MTFs are better without. 

The Oly 17mm f/1.8 has a raw distortion of 4.5%. As a consequence there is simply quite a bit of stretching and interpolation going on in the border region. 

Since this is enforced in MFT land, it is hard to get around this.

 

Interestingly CaptureOne 7 provides the uncorrected image from RAW now. 

It is probably hard to tune this but I could try to provided the RAW MTFs besides the 'corrected' MTFs.

Not sure in how far this is helpful though.

 

The results aren't bad for the 17/1.8 but they stay way short of the 75/1.8, of course (which doesn't need any auto-correction).
 

I think at some point you have to penalise them.  Either you report top MTF and give them poor marks in the distortion department or you fry them for poor boarder performance but give them a good rating for low distortion.  I think, since most people use the distortion correction and suffer the poor boarder performance the later is more relevant to how people use these lenses.  Your comments seem to imply that this (measuring MTF and distortion with distortion correction "on") is what you are doing.

 

On your comparison of the 17 to the 75, I would never expect a medium WA for digital to come close to a medium length telephoto.  Just to much physics against you.  Compared to the 75 the 17 is a cheapo.

 

I am looking forward to your review of the 17.
enjoy
#15
I just did the reference check based on the RAW data.

To my surprise the MTFs did NOT improve.

#16
Does this lens suffer from high field curvature in the corners ?

#17
The 17mm f1.8 could be worst at the focal length at which MTF tests are done.

At least that could explain the discrepancy between MTF values and real world samples...
  


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