Hi! Right now the 4/3 goes for $400 in mint condition, the m4/3 goes for more like $600. I understand that the m4/3 is smaller, and weighs a little more than half as much. It would definitely also focus faster on my E-M5. I've heard that the 4/3 has slightly better image quality. See this thread: https://www.mu-43.com/showthread.php?t=45582 DPReview says the below here: http://www.dpreview.com/lensreviews/olympus_m_9-18_4-5p6_o20/4: "The M Zuiko Digital ED 9-18mmm F4-5.6, perhaps unsurprisingly, has broadly similar optical characteristics to its Four Thirds cousin, which is no bad thing. However there is some penalty for the compact design: the extreme corners are a little soft, especially at the wide end, and chromatic aberration is noticeably increased." Here there seems to be the reverse sentiment, even though in the pictures in the thread, I see a bit more resolution--and possibly also more microcontrast--in the zd lens: http://fourthirds-user.com/2010/05/mzuiko_918mm_f456_sample_images_and_comparisons.php http://fourthirds-user.com/forum/showthread.php?p=56860#post56860 Here are some examples, pictures from that article: f5.6 img #10: zd: http://fourthirds-user.com/sample_images/274/P5240071.JPG img #8: mzd: http://fourthirds-user.com/sample_images/274/P5240069.JPG f5.6 img #26: zd: http://fourthirds-user.com/sample_images/274/P5240087.JPG img #23: mzd: http://fourthirds-user.com/sample_images/274/P5240084.JPG f8 img #46: zd: http://fourthirds-user.com/sample_images/274/P5240108.JPG img #47: mzd: http://fourthirds-user.com/sample_images/274/P5240109.JPG I already have a 4/3 to m4/3 adapter, so that's not an issue. If I intend to use manual focus, and the extra ~115g of the 4/3 lens doesn't bother me, is there any reason to pay the $200 additional for the m4/3 lens? Does anyone here have any experience with both of these lenses? Thanks!