As we all know, this lens received rather poor rating and adverse comments at the PhotoZone and then the official early samples posted by Ned Bunnell did look bad either.
But then stupid fanboys of Pentax like me are actually irrational ;->, I went bought this lens regardless of the poor reputation of this lens all over the Internet! :-o
This time, I am going to write a practical review on the lens, with more real-life photos of mine shown, for what this lens can deliver, on a K-5. You will see how "poor" this lens could be!~
First of all, still some comments of mine in words. As you can see from the above modelling photo, this lens is really compact and lightweight. It has an internal focusing mechanism such that the length of the lens will not change during focusing. And of course, the front element will not rotate.
I am much impressed with the build quality of this lens, which is the best amongst all DA Pentax standard zoom lenses that I have ever used, I would say. Even the bundled lens hood is better built than most of other Pentax', with matted lining inside and the rugged texture outside which contributes to a solid feeling. At the beginning, maybe owing to the weather sealing, when the lens was first opened brand new out of the box, it is very tight to zoom. But then after the first few days of use, the friction and resistance became just right provided that it is not zoomed too fast and too quickly otherwise higher resistance can still be found.
Speaking of the DC motor and its AF performance on K-5, it is fast, moderately accurate and silent although it is not completely silent and some very small sound can still be heard in really silent environments (ditto for the new Canon STM, which I also have). Under the Live View mode and with this DC lens, the LV CDAF is obviously faster than with other conventional type Pentax AF lenses.
Now, let's come to the IQ part, this lens is quite sharp in the image centre throughout the whole zoom range and from wide-opened, here are some various samples (Click to download in Large size, EXIF preserved):-
(18mm, f/3.5)
(18mm, f/5.6)
(18mm, f/6.7)
(21mm, f/4)
(21mm, f/8)
(28mm, f/4)
(36mm, f/4.5)
(36mm, f/6.7)
(36mm, f/8)
(40mm, f/7.1)
(53mm, f/6.3)
(100 mm, f/5.6)
(135mm, f/5.6)
It can be noted that the extreme corner softness is only existent at the widest side at 18mm. From 21mm and onwards, the effect is considerably eliminated and is not that noticeable. Distortion is significantly decreased, too.
In general, images produced are with good colours and contrast. Resolution is high throughout the frame except at the extreme focal ends, i.e., 18mm and 135mm. I do note that my lens' optics are perfectly centred by judging from the vignetting pattern, nevertheless. Maybe I am just lucky enough.
The flare resistance is superb. Look at this:-
The bokeh of this lens is not bad, look at these two (and also some of the above samples with a blurred background):-
Round bokeh of highlights can be seen.
Btw, why to use Live View with a DSLR? (I can see many DSLR beginners have been doing this!) Why not just use a K-01 if so?! :-o
There is one minor problem of this lens (or maybe the Pentax DSLR system in general), it is that it has a slight underexposure tendency, a +0.3/0.5 exposure compensation would usually cure it.
Besides, the Pentax SR system for tele-lens is proven to be ineffective, once again. I have got quite some blurred photos when shot at 135mm, just because the lens speed is slow but SR didn't help:-
All in all, I am quite satisfied with my copy of the DA18-135. It seems that my lens has far better performance than what is shown in the various measurbation tests and I do believe that it is a lens that performs well in real world but not so for measurbations. This maybe owing to the inconsistency quality control (or lenses are actually classified into different quality classes and batches - mine was purchased separately). The other possibility is that the optical design of this lens is not optimised for close range objects, where a test chart is placed and shot.
At the end of the day, this travelling zoom will not give you stellar optic quality which primes could give which is well expected, After all, let's see if my "favourable" review this time could retrieve the confidence of some potential buyers of this lens and maybe also for Pentax the brand as well! ;-D
Related:-
Interview with the Optical Engineer/Designer of the DA 18-135 Lens