Originally posted by Bui Hello, yes in fact a very obvious solution would be purchasing another 15mm. However, the decision is a little bit more complicated because:
- During the time I have acquired the 16-85 -> I have a backup wide option for when I need it. Before the 15mm was the only wide angle lens I have.
- (Also in relevant with point 1), now I have a chance to buy a new lens, I'm thinking, why not trying something new, as I already know the 15mm, something that can offer even wider view, for example, the Sigma 10-20, or Pentax 12-24, etc. But yeah obvious downside is the bulkiness. I don't take wide photos that frequently to be able to dedicate a room for such big lens in my bag everytime.
As you state, the most remarkable thing about the DA 15mm LTD is you get an extra-wide angle lens having exceptional performance in an amazingly small body, yet of top-notch build quality. So its smallness is perhaps its most amazing and attractive attribute.
Performance-wise, your DA 16-85mm lens, while great for an all-around zoom lens, is large, and bulky. Distortion at 16mm cannot even approach the very good performance of the tiny 15mm LTD. The LTD does have some noticeable vignetting wide open, however the DA 16-85mm has yet more at the wide end. But to get low distortion at such a wide angle in such a tiny lens is amazing. Now, the matter of linear distortion might be moot if you do nature landscapes. Not likely to be visible. For cityscapes. architecture, or other linear objects, then it matters.
But the best in that regard is the really excellent DA 12-24mm f/4, which also easily beats out the DA 15mm LTD in edge-of-frame performance up to f/8. Even at 12mm distortion is not bad. Filter size is 77mm, conveniently the same size as numerous fast f/2.8 lenses. (thinking of polarizing and ND grad filters) Its weakness is in having high CA's
A very strong contender is the Sigma 10-20mm f/3.5 EX DC super WA lens. It also offers silent DC AF, where the Pentax 12-24mm uses the old (but reliable) screw-driven AF. Linear distortion is higher at its wide end than the Pentax 12-24mm, but still not too bad, and now we are talking 10mm, while at 12mm it would be similar, and again at 15mm is virtually gone completely, very comparable. Then it really makes sense to own both lenses because while the DA 15mm f/4 LTD is the compact alternative, the Sigma 10-20mm f/3.5 can go a LOT wider, but is a LOT bigger. It is heavier than the Pentax zoom lens, due to being a bit faster- f/3.5 vs f/4, and wider- 10mm vs. 12mm. No unusual CA problems. At 10mm only, corner of frame performance is soft, but edge performance is very good to excellent. But how important are corners compared to edges? How often is there something of importance in a corner? And with the Pentax, 10mm does not exist. Filter size is also larger at 82mm. But step-down rings could be used for other lenses of 77mm filter size. Right now, B&H is running a fantastic price on this lens. So fantastic I just ordered one, thanking this thread for my discovering the deal!
The Pentax zoom offers more at the long end, while the Sigma has more at the wide end.
Last edited by mikesbike; 08-27-2019 at 11:48 AM.