sony a7r vs sigma sd1 18-35mm resolution test

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docmaas
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sony a7r vs sigma sd1 18-35mm resolution test
4 months ago

These are shots of a koren 2003 resolution chart using the a7r and sd1 with the 18-35 f18 lens.

camera to target distance same for all images.

all images are unmodified except that sharpening has been set to -7 for the sigma

white balance on both was set to auto

aperture priority mode was used compensation was set to 0

as usual sigma needs more care than I gave it. sony was much better in this respect

a7r shot full frame mode at 27mm.

SD1 shot at 18mm

SD1 enlarged via lanczos in Irfan view (b-spline and simple resize lower quality but same cutoff)

The amplitude of the max mins indicate the shades of gray so the low point is white and the high darkest. The lower the amplitude the lower the mtf or resolution (the less amplitude the closer the max is to the min and the less the difference between the two in degree of gray.

The x axis is length of the measured target in pixels nothing to do with resolution

These are relative measurements only and cannot be compared to any other measurements.

the flattening of the response indicates extinction.

There is more information on koren and ImageJ here: http://www.normankoren.com/Tutorials/MTF5.html

Under these conditions sigma does not match A7r full frame images when upsized appropriately by a factor of 1.5.

The images of the Koren charts are full size crops of the charts from the images as shot for the sony and uprezzed x 1.5 for the sigma.

full size crop of chart photographed image A7r

On these charts the top band and the fourth band are sin wave resolution charts running from 2 to 200 lpmm. But those numbers are only relevant if the charts are used as directed on the Koren link above THEY ARE NOT RELEVANT HERE. The second band is the same lpmm in linear format. I used the 4th band for the analysis.

ImageJ resolution plot of chart from A7r

full size crop of chart from SD1 uprezzed x1.5 on Irfan view using lanczos algorithm

ImageJ resolution plot of uprezzed chart from sigma SD1

Remember:

The images are unmodified with the exception of reducing the sharpness setting on the sigma.

They are only indicative of what the camera/sensor/lens SYSTEM is capable of without modification by a user.

The resolution difference is what I was looking for the the fact that the sigma drops off earlier than the sony indicated that it can't keep up in pure resolution.

The graphs are logrithmic and should not be interpreted linearly. The differences are greater than they appear when looked at linearly.

You can use the lpmm scale at the bottom of the actual chart to see the relative differences.

I will now don my fireproof suit and await the arrows.

Mike

Leica X1 Sigma SD1 Sony Alpha 7R
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