Loga: This DOF comparsion (if it is intended to be) is simply a lie. To get the same framing with the 25mm you should step back a little (or more, depending on the subject distance). But if you do this, the DOF changes because the subject distance changes.
With the same framing the DOF difference will be noticable, but quite small despite the slightly wider aperture and the slightly longer focal length.
I understand the intention of Dpreview to show the difference in field of view, but they should have been so ambitious to make a correct comparsion in terms of DOF.
Dpreview, please take some photos with the same framing, with short subject distance to see the _real_ difference in DOF. Thanks :)
I found a test with the correct comparsion of DOF. With the same framing the DOF is _almost the same_. For anyone who wants to replace his 20mm because of shallower DOF: DON'T! You will get nothing.
The real difference: different FOV, 25mm is a slightly faster lens (0.5 EV), has faster and quiet AF, is better for closer portrait, but 20mm is smaller, and cheaper.
Okay, this lens is good, but BIG. I want this for m4/3:
This is an 50mm eqv pencake. If it had f2.0 that would be the ultimate lens for me.
ginsbu: Thanks for the update to add the comparison shots with the same framing. Not to be too demanding, but could we see the wall shot from the 25/1.4 at f/1.8 in addition to wide open? That would provide the most direct comparison between them.
If the wall is normal to the field (or: parallel the lens, and it is I suppose) then every brick or none of them should be in focus or out of focus - at least at this subject distance. Just my 2 cents.
Anyway, IMHO in this case someone should choose rather based on FOV, taste of image (color, contrast), size, AF or price issues, not on DOF control - simply because the difference in this dimension is almost non-existant. This Leica 25mm seems to be a good performer, however, not a real portrait lens (and I don't think it has been intended to be). You can take environmental portrait with the 20mm too, and take a little closer with 25mm, but I suppose (maybe I'm wrong) you can't take head portrait with the 25mm either due to perspective distorsion (at least 45mm needed).
And one more thing with DOF: don't be disappointed because the new oly is 1.8 and not 1.4. It seems almost the same DOF. But in terms of shutter speed (and therefore ISO settings) it does matter.
This DOF comparsion (if it is intended to be) is simply a lie. To get the same framing with the 25mm you should step back a little (or more, depending on the subject distance). But if you do this, the DOF changes because the subject distance changes.