Fuji XF18-55 lens optical behaviour

Started Feb 23, 2013 | Discussions thread
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Cliff Beard Regular Member • Posts: 447
Fuji XF18-55 lens optical behaviour

I have the Fuji X-E1 and have been shooting with it and the 35 prime for a couple of months.  Generally really loving that combo.

Last week I took delivery of the 18-55 zoom as I want it for a travel lens and for day to day walkabout stuff with my 2 year old, where its versatility will help.

I'm really impressed with the build, ergonomics and AF performance and generally the optical performance in real world shooting seems very good indeed.  I always do some tests of new lenses to check for any obvious optical issues, which consist of some general snaps using different focus points and apertures and 3d subjects but also the "brick wall test" using a tripod and trying to accurately align the camera to the planar target.  I was about 2-3 metres away so fairly close.

I am noticing some slightly unusual behaviour in the tests at 18mm using a planar subject; at f2.8 the entire image is really very sharp indeed, with only a very minor and even softening in the far corners.  Upon stopping down to f4 the lower left side softens considerably and this does not improve much at f5.6. The right side seems to undergo a less drastic softening.  The brick wall images showed a significant softening in the corners, especially at lower left.  On a series I took of a cycle the front tyre (at lower left) was sharp at f2.8 and soft at f4.

When I actually focused on the wall at lower left, the sharpness did improve (not great) but the rest of the frame was soft.

Has anyone noticed if there is some significant field curvature or other similar issue at play in this lens.  It has quite a complex optical formula after all.  It just seems strange that stopping down seems to reduce image quality in areas outside of the centre area rather than improving it.  If so it seems pretty drastic

I am wondering if there may be a centring defect or similar problem at left, but the f2.8 images seem very good in that area, which would be odd.

When I shoot real world images and at other focal lengths I struggle to see an issue but the test results did not give me confidence.

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Fujifilm X-E1 Fujifilm XF1 Panasonic Lumix DMC-F5
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