Virtually any lens will be at its best at a certain aperture setting, usually in its mid-aperture range. Most Pentax models have long had their MTF settings for shooting in P mode, so the camera will take advantage of this to set the best quality aperture when lighting permits. However, that does not mean poor quality at other apertures. Also, most lenses, even of the best quality, will usually not be as good for resolution at the frame edges as in the central area. Then, zoom lenses, even the best, are commonly not at their best when zoomed to the extremes of their zoom range. Degree of importance of all this depends on how picky is the individual, what kind of viewing and to what size will be the images used, and what kind of shot the lens is being used for. The DFA 28-105mm is at its best when used on the K-1 or K-1 II, for which it is designed. It can then deliver higher resolution (36mp) compared with a similar shot from the same distance on APS-C (24-26mp max) with a shorter zoom lens, also of very good quality.
Since the OP is interested in zoom lenses for travel, and with a K-x body, the DFA 28-105mm would simply not be ideal for this purpose, as would other options. If using the K-1 or K-1 II, that is a different story. Since this lens being considered seriously is with its shortest 28mm FL, whether the optional lens to be considered comes with either a 16mm or 18mm short end is rather a minor factor. Then getting into prime lenses is a whole other ball game, and the question of why comes even more to mind, as then we are talking about the prospect of even more lens-changing on the trip.
The very versatile DA 18-135mm is a fine performer, capable of very fine quality imaging, and would be perfect to get the most shots with fine results, while keeping lens-changing to an absolute minimum. It is virtually the ideal travel lens. Its AF is superior- one of the best- a big factor, especially with older cameras, and performs exceptionally well even with these older camera bodies, advancing their AF capabilities considerably. Despite its exceptional zoom range, it is relatively compact to go with a compact camera body, yet it is very well built. It has a very good record for QC, most often getting a perfect lens right out of the box, a better record than has the DA 16-85mm lens, which is a very good lens when getting a good copy, but which also is more expensive and significantly bulkier, yet does not have the extended telephoto range.
In one case, I shot a parade situation with the DA 18-135mm lens on my K-5 IIs. I got shots coming up the street from the bottom of a hill. Some of these were at or near the maximum 135mm to compress distance some, where this lens has been measured and evaluated to be at its worst- no surprise. Lighting was bright daylight. Yet these images turned out surprisingly good upon viewing on my high-resolution computer screen. Near frame edges which had measured in lab tests at this FL to be at the absolute worst, were actually not blurry as one would expect them to be. Upon using my controls for a blow up, I could read the parking signs near the edge very clearly- a pleasant surprise, as was the overall very good outcome of the scene. Other images came out great indeed. I could get groups in some shots, and instantly zoom in on an individual in other shots, all with fine quality. Then as they were near the edge of town and marched into the countryside, I could get a good part of that in to include the marchers in a landscape shot.
Lab tests have shown resolution to be in the excellent range in the frame's central area until well into the tele range where it is still very good to excellent. Edges of frame are very good at shorter FLs through 50mm, and even a very small stopping down boosts that performance. As zoomed farther into the tele range, the frame edge sharpness gradually diminishes, but is generally of less interest anyway. Also, very capable of delivering impressive closeups, with bokeh that is quite good. A very impressive performance, especially for a compact lens of such zoom range.
A few years ago, I upgraded to a KP from my K-5 IIs, though I still sometimes use that body. Of course I regularly use my KP with my DA 20-40mm Ltd, sometimes pairing it with my DA* 50-135mm f/2.8, as well as also using some Limited primes, and other top-quality lenses. It did not surprise me that the improvement in IQ from the KP, compared to images from my K-5 IIs, is a visible improvement when using these top-level lenses. Not huge, but visible. However, when I needed the zoom range of my DA 18-135mm, I did not hesitate to employ it on my KP. Another unexpected pleasant surprise was, the KP's improved imaging over those taken with the K-5 IIs was still visible with this lens!
Some have reported zoom creep with this lens. I've not had this problem, but then I do NOT carry it with my camera hanging around my neck. I draw the camera out of my holster-type case when I'll be using it to shoot. The zoom action is as perfect as it was over 10 years ago when it was new.
Last edited by mikesbike; 04-01-2022 at 08:59 PM.
Post #3 by mattt
Similar Threads 
