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

Started 10 months ago | Discussions thread
DonSC
Contributing MemberPosts: 987
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Plus perception and slightly different in focus areas
In reply to rhlpetrus, 9 months ago

According to the OP, he took the shots from the same distance and then cropped. That's probably the best way but it does introduce some issues. First is that it's tricky to exactly match FoV and DoF for bodies with different sized sensors. For example, with a 50mm lens on a FF body, shooting at 5 feet and f/2.8 you get a DoF of .5 feet. With a 25mm lens on a 43 body, shooting at 5 feet and f/1.4 you get a DoF of .51 feet. Not a big difference but it's a difference.

The second issue is that the cropping introduces the problem of perception.  If you shoot from the same distance, in order to get the same FoV the image from the shorter FL lens has to be cropped more heavily. As a result, the longer FL lens will appear sharper, making the contrast between the in focus and OOF areas more dramatic.

I haven't done it, but I suspect that if you eliminate the in focus subject, and only look at the OOF areas, you won't see much of a difference. In essence part of what we're looking at is a perceptual differences aka an "optical illusion".

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