MFT 25mm f/1.4 fails to blur background like Full Frame 50mm lens @ f/2.8

Started Feb 16, 2014 | Discussions thread
Mike Dobbs Senior Member • Posts: 1,089
Re: MFT 25mm f/1.4 fails to blur background like Full Frame 50mm lens @ f/2.8

bluelemmy wrote:

Shot 1, the flash is fuzzy, shot 2 it sharp. Shot 1 is at low ISO, 2 at 3200 ISO so the comparisons are invalid - plus any difference in cropping makes the comparison invalid.

For a given distance, DoF is governed by the size of the hole the light comes through. 50/2.8 = 17.86mm hole, ditto 25mm/1.4. That's it.

But, the focal length of a lens is only nominally correct at infinity (and even then a 50mm is often 51.5mm or 49mm or something similar). When focal point is closer than infinity, there is an effective change in the focal length of the lens and that can differ according to lens construction and design.

In other words, the two lenses you test are identical in theory but not necessarily so in practise.

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That makes sense. Doesn't aperture blade design also make a difference in OoF effects?

I'd like to see a test of several different manufacturers lenses of the same focal length on the same camera, same test shots. Should be easy to find several 25mm, 17mm etc lenese for mFT cams...

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