Please note that I'm an amateur photographer, and have never changed the kit lens of my Sony NEX-F3. These are my first steps into the world of “prime lenses”.
A prime lense is a camera lense with a fixed focal length, i.e. it has no zoom. If you want to change your field of view, you have to move closer or further away from the subject of your photo (“zooming with your feet”). So why on earth would professional photographers trade in zoom capability for a prime lense? Because the image quality of prime lenses can be far suprior: less image distortion, less optical abberation and a lense formula that is optimally designed for its focal length. Zoom lenses are often a compromise, or a very expensive piece of hardware.
With some spare cash, I've opted for the Sony SEL-50F18 OSS and Sony SEL-16F28 lenses.
SEL-50F18 OSS—The portrait lense
The SEL-50F18 OSS is a fairly new lense with a fixed focal length of nominal 50mm, and a maximum aperture of f/1.8 (which is really great for low light shots). The optical image stabilization (OSS stands for Optical Steady Shot) of this lense allows you to capture night or party scenes without flash, but still at low ISO ratings.
To be upfront: I love this lense! The 225€ were very well invested. The lense is dubbed as “portrait lense” because of its 50mm focal length. It dives into the scene quite a bit more than the human eye. This is great for portraits, yes, but I found another application: the lense does an excellent job at taking close-up pictures of items, e.g. for product reviews or this blog. The wide f/1.8 aperture creates a wonderful and creamy bokeh (blurred background), so people or objects in focus stand out of the background really great. This feature alone makes the SEL-50F18 OSS a must-have lense in your photo bag if you own an E-mount camera. The wide aperture also allows for very short exposure times, making it a very “fast” lense in broad daylight. Here's a picture of the lense, and some sample photos from Paris:
SEL-16F28—The pancake lense
The second lense I bought was the SEL-16F28, a wide-angle lense. I got it used from eBay for about 130€, which was a good deal. What this lense has going for it is its small size: when it is mounted on my NEX-F3 camera, the setup almost becomes a compact camera. This might be a great feature if you want to take pictures in restricted settings, such as concerts. A camera with this pancake lense will easily fit into your jacket.
Now, there was a reason why I bought this lense second-hand: I was warned in other blogs about the rather poor image quality. I have to say this is true: at wide apertures, this lense produces highly blurred images, especially towards the edges. I really like the idea of a wide-angle lense, though, and might get a better one for my camera in the future. Needless to say, I've already sold this one.
In some settings, 16mm focal length is just what is needed to take photos with spectacular perspective—surprisingly, this goes for portrait shots as well! I have taken a great portrait of a friend sitting in front of the Louvre pyramids where the wide-angle makes the picture really stunning. Unfortunately, I have no permission to post the photo here.
To wrap this review up, the pancake lense has no reason to exist: my iPhone SE takes better and sharper pictures with its back camera than this lense attaached to my Sony NEX-F3 (remember Phil Schiller talking about “Deep Trench Isolation” in the iPhone 6S and SE cameras). Smartphone cameras are usually equipped with a wide-angle lenses, though not as dramatic than 16mm focal length—but they will do a better job!