On 6/19/2015 11:44 PM, C.H.Ling wrote:
Just found an interesting issue with the lens angle of view on the newer vs older M4/3 bodies and also Viewer 3 vs
RawTherapee.
...
The angle of view is further widened on both images.
I previously posted some distortion correction images with the 12-50 and the Panny 12-32 lenses. I didn't point out the
difference in AOV at the time, and it's not as obvious as it might be, as I sized everything the same.
<http://www.moosemystic.net/Gallery/tech/DXO/LensCorrect.htm>
Here's a more real world sort of image (i.e. one I already had at hand.) All the versions retain their size relationship
to the original Raw file, so you can see where there is expansion vs. compression.
<http://www.moosemystic.net/Gallery/tech/DXO/_A001643_dist_corr.htm>
I made no effort to deal with differences in other aspects. May be unfair to RawTherapee, for example, with its blah
rendition, 'cause I'm unfamiliar with its defaults.
As many of you know I prefer Olympus RAW converter but since E-P5 I found the image edges are very chunky, looks over
sharpened with USM at high radius (say 1.5-2 pixels) even I set the sharpen to minimum. This forced me to look for
other RAW converters. widened.
Further checking the images after this discovery, I believe Olympus has made the following process to its image on
both JPEG and its RAW engine:
- linear distortion correction
- chroma and fringe adjustment
- crop the image heavy
- Resize the image to fit the pixel size, in that case enlarge the image to fit
4608x3456 on the E-P5
4608x3456 is the JPG size. The Raw file size is 4640x3472. Both DxO and PtLens enlarge the image dimensions, not
overall, but mostly in the corners as a result of barrel distortion correction.
The last process creates a big issue on the natural look of the image, which looks realy bad for pixel peeping. Now I
understand why the images taken with my OM Zuikos looked much better than the 4/3 native lenses as no
correction/cropping is done with the non native lenses.
I partially chose this image for the fine leaf detail in the corners. I have previously noticed some significant
deterioration in the far corner of a SWA image corrected with PTL. In that case there was a beer/soda can on the ground
which was distorted and softer after correction. In this sample, at 100%, the corner detail looks fine.
You are certainly correct that Oly is cropping the post correction image (and ACR is obviously using the same exact
algorithms). However, I don't see where they would be up-sampling. I suspect the whole image is enlarged in the
correction process (why?), then simply cropped to size.
Comparing the angle of view of my old 11-22 at 11mm and the 12-24 at 12mm, I believe the 12mm is much narrower than
quoted on a E-P5 with Olympus Viewer. As you know even half a millimeter counted at wide angle, it is too bad to see
the result like that.
This is a tricky business. There is sample variation, and as you point out, even small variations have a big effect on
AOV. Modern Photo allowed FL variation of ±5% in their tests. Here are the results for some OM lenses:
FL Spec. FL Meas. Var.
Zuiko 18/3.5 18.76 4.2%
Zuiko 21/2 20.15 -4.0%
Zuiko 40/2 41.33 3.3%
Zuiko 50/1.2 52.48 5.0%
Zuiko 50.1.4 50.94 1.9%
Zuiko 50/1.8 51.87 3.7%
Zuiko 90/2 90.44 0.5%
Zuiko 100/2 100.65 0.6%
Zuiko 180/2 180.57 0.3%
As you can see, the particular samples of the 18 and 21 mm lenses varied a lot,
and in opposite directions.
FL Spec. AOV FL Meas. AOV
Zuiko 18/3.5 100.5 18.76 98.1
Zuiko 21/2 91.7 20.15 94.1
The assumed 9° difference in AOV is actually 4°. As a result, it might hardly
be worth having both lenses!
The results with another pair might go the other way.
Comparing the spec. 11 mm of one zoom to the 12 mm of another can't be generalized; it only applies to those particular
samples.
View Point Moose
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