Corner sharpness: Four Thirds vs 35mm (bandwidth warning)

Started Oct 27, 2007 | Discussions thread
Stu 5 Veteran Member • Posts: 3,277
Re: Corner sharpness: Four Thirds vs 35mm (bandwidth warning)

Ominous wrote:

Amin Sabet wrote:

Stu 5 wrote:

That is why you use a lens testing chart....... they are flat so
there are no D.O.F problems.

Life has DOF. Why create a scenario for testing that doesn't apply
to real life?

Are you testing DoF, or the lens corners?

You can't say a lens has soft corners if the shots you are taking the
corners are simply not in focus.

Exactly! The way these lenses have been tested you can't tell if the lens has soft focus on the edges or if it's out of focus. It's all right going on about 'life has DOF' but when it comes to testing lenses your testing needs to be controlled or the results are meaningless but worse than that, misleading. You need to use a lens chart on a wall and a camera on a tripod that is parallel to the wall, with the lens framed on the centre of the chart. You then take photos with both lenses through the whole aperture range on the lowest 'iso' setting on the camera. You then can look at the resulting photos and use the chart to measure the 'lines' per 'mm' reading in the centre and on the edges. You will also be able to tell if the lens suffers from pin cushion or barrel distortion as the chart has readings for that as well. Rule of thumb is that a lens performs best one f stop from fully closed BUT this is not always the case everytime. As I said before the only reason I know this is because I have studied lens design and have done lens testing.

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