Originally posted by don_park Recently I bought Pentax K-3-2 and two Pentax lenses, i.e. HD DA 15 f/4 L & FA 77 f/1.8. My primary interest is landscape photography. Although the 15mm shows a perfect field of view, I am disappointed with the image quality, esp acuteness(sharpness). I could have chosen the 12-24mm zoom instead, but I wanted a prime Limited lens. Do I need to consider selling my new HD DA 15 for smc DA 12-24 for better lens performance? In the meantime, I'vd added a Sigma 18-35 f/1.8 Art to make up for the wide angle gap. Will appreciate valuable advices from Pentaxians.
To be clear: the technology to make small and perfect 15mm on K mount or any equivalent mount (Canon, Nikon) doesn't exist. The registration distance is too long compared to the focal length.
So there basically 2 solutions, you'll make a small/light lens like the DA15, this lens will have great constrast, flare resistance and will be light in the bag. The max apperture will be soso and the performance not perfect, for sure. In case of DA15, borders are ok at f/8.
Or you make a much bigger lens with lot of glass. Flare will not be well controlled at all, contrast reduced, but you'll get a large max apperture and more sharpness, in particular on borders. That for example the Samyang 16mm. This kind of lenses are huge.
Last alternative, make it a zoom. You'll get flexibility, something big/heavy but loose basically the large apperture. Example Sigma 8-16.
So the question are what are your priorities.
DA15 handle contra light and flare like no other and has exceptionnal contrast control. It does fantastics shoots in practice, but has limited border sharpness. It is very small/light meaning you can always have it in the bag while a huge UWA zoom/prime will often stay at home.
If you prefer to get something sharper and able to zoom, what I got is that the 8-16 is the sharpest ultra wide angle lens in K-mount. DA12-24 is great, but not as sharp. Good thing of 12-24 is it is still smaller.
For a prime, is size is no concern, I'd think of some Samyang lenses like the 14mm f/2.8 or 16mm f2. They are different so you should choose depending of your priorities.
Now a few DA15 pictures... You can click to zoom...