Originally posted by pepperberry farm
What i want a prime for: portraits, landscape and as a walking around lens...
Is a 35 mm lens that much of a different view than a 50 mm? Is an aperture of f1.8 that much more noticeable in low light than an f2.4? Should I be looking only at autofocus lenses vs manual?
I've read from end to end the thread on old manual lenses and how great they are - but is it really just the 'neat' factor of using an old lens vs a new 'plastic fantastic'?
Curious what your background is in photography? Are you an ex-film geek like me or new to the whole thing?
Also what is your budget?
In the meantime let's see about these questions.
1) 35 vs. 50. The answer as indicated by others is accurate; this is a big difference. If you have the kit lens you can show this to yourself by taking a day to shoot nothing but 35mm or 50mm and then another day with the opposite requirements. The fact is that 50mm was the "Normal" lens on old film 35mm or current "Full Frame" digital cameras but on APSC which is the size sensor you have on the K50, the "normal" lens is a 35mm. The 50mm is more of a short telephoto and portrait lens (just at the low end of that range) However with room to move back this is less of an issue - indoors it is a problem, outdoors not so much.
2) AF vs. Manual. You will get many answers but MY answer is get the AF lenses for now. The ability to manually focus on the K50 is so so, through the use of Live View you can do focus peaking and you can use focus confirmation via the viewfinder but these are a poor substitute for split prism focusing screens like we used on manual film bodies.
3) Religion vs. Science. A lot of cult like info exists and few people take the time to be careful to directly compare old primes vs. today's lenses. There are many fantastic lenses of all ages - and some of the things that drive the acceptance of a lens vary from person to person. As an example, many older lenses exhibit significant purple fringing. Modern lenses are designed with this in mind and often (but not always) perform better in this respect. This is just one of many factors.
Now back to the start; a prime to fulfill these functions on APSC here is what I think of for each:
Portrait - typically between 50-135mm and large fast opening f/2.8 or better
Walk about - typically between 20-50mm (or larger range) and medium fast opening f/2.8 preferred but not required
Landscape - typically between 10-20mm and speed is not important since most shots will be f/8 or slower.
The point is these are three completely different optimizations. The specific focal range and f/stop can vary and there are plenty who would have different opinions, the point of my listing them is to give some guidance not to set anything in stone.
In terms of price I don't think you really set your budget out but let's talk about options.
A)DA 50 f/1.8, F/FA 50 f/1.7 - Long but usable for walk-about, fast enough for that and just long enough to use for portraits. F is the sturdiest, DA is the cheapest and most modern optimizations. All of these almost the same.
B) DA 35 f/2.4, DA 40 f/2.8 (Limited or XS version) - fits the walkabout category, fast enough, not too tight for "normal" perspectives. Doesn't provide that classic rangefinder street photography angle of view that the DA 21 or an FA 24 would provide. These lenses also fit the walk around but are more expensive.
C) Nothing particularly cheap in the landscape class that stands out. The DA 15 is fantastic but not cheap.
There is no single lens PRIME option that fits all of these but a two lens kit can come close. The DA 21 f/3.2 and the DA 50 f/1.8 (or F/FA 50 f/1.7) is probably the closest you can get. The 21 is a bit narrow for some landscapes but great as a walkabout and the 50 is a bit short for portraits but not bad. The fact that you can turn your camera vertical and use the 21 or the 50 to make a stitched panorama means the lack of the ultrawide landscape lens isn't really a huge loss. Where this fails is indoors where the distance minimum for the framing you want may not be there with the 50 and the 21 may seem too slow but don't be afraid to push ISO a bit.
The other way to go would be to get a high quality zoom like the 16-50 f/2.8 which fills all these roles and more.