I´ve owned both, and agree with Hermann. The 10x42 glass is outstanding. I could discern more CA than I would expect from an "alpha", but it wasn´t a problem. The IS system in the unit I had was flawless, far better than in other models I´ve had. Views were stunning, very warm crisp images. However, it was a beast to handle. Dodgy eyecups, and brick-like in the hand (especially compared to the comparatively cute 10x30). I reckoned the weight and handling weren´t a sufficient trade-off for a mag of only 10x. I have the 15x50 now, and although the image quality isn´t as good, it´s easier to handle (same weight, but easier to handle), and the 15x fills a niche for me by giving me that much extra reach. I would recommend you try a 10x42 for a few days in the field, if you can, before making a decision.