Pentax FA 28-105 f3.2-4.5

Pentax has released three different zoom lenses in the 28-105 range, all of them falling in the FA series: (1) FA 28-105 f4-5.6 PZ; (2) FA 28-105 f4-5.6 [IF]; and (3) FA 28-105 f3.2-4.5. The first of these lenses was released in 1991 and featured Pentax’s rather gimmicky “power zoom” feature. In the late nineties, Pentax, eager to get rid of the power zoom lenses, replaced the original FA 28-105 with a lens licensed from Tamron. This was merely a stop-gap lens to give Pentax engineers a chance to design a new 28-105. In 2001, Pentax released the FA 28-105 f3.2-4.5, generally regarded the best of the three FA 28-105 lenses. The first two 28-105’s had been a bit on the slow side, particularly when compared to the competition from Nikon and Minolta, both of which sold 28-105 zoom lenses with an aperture ranging from f3.5 to 4.5. Given how popular 28-105 zooms were in the nineties, Pentax’s slower offerings helped make their brand look more appealing to consumers. The FA 28-105 f3.2-4.5 was an attempt, I suspect, to give people an incentive, however small, to prefer Pentax over the competition by providing users with a slightly faster 28-105 zoom lens. Unfortunately for Pentax, when this faster version of the FA 28-105 was released, the camera world was about to be turned upside down by the revolution in digital. The FA 28-105 f3.2-4.5 would be one of Pentax’s very last film lenses.

The lens itself has both its good and not-so-good points.. Like most of the 28-105 zoom lenses from the nineties, it performs better in the middle range rather than the two ends. Indeed, between 50mm and 70mm, it is a very fine lens. Elsewhere it has issues. These issues are most apparent at the wide end, which suffers from poor border to border sharpness and annoying fringing issues.

Let’s first.take a look at the fringing issues. This is mostly a problem at the wide-end of the lens. Here’s a crop from an image taken at 28mm:

Now quite a few zoom lenses and ultra-wide primes will fringe like this. It’s not uncommon, nor it is anything to get real uptight about. The question must always be: how easy is it to remove these fringes in post? Some lenses it is relatively easy. The DA 12-24 is an example. That lens fringes quite easily yet it usually fairly easy to clean up the fringes in post. The FA 28-105 can be a bit more challenging. After several minutes of fussing about, this was about as good as I could do:

The fringes here are significantly reduced, but not taken out altogether. What is even more frustrating, we’re not even talking about branches against a washed out sky: this is merely a hard contrast edge. The lens definitely has issues here.

Fringing can still be present at other focal lengths, but by 50mm it is relatively minor. This is mostly a problem in the 28mm to 40mm range, with issues worsening as one goes to the very widest focal lengths.

Fringing is not the only issue plaguing the lens on the wide end of things. Corner to corner resolution is another problem plaguing this lens at wider focal lengths. Consider the following image, taken at 28mm, f8:

At web resolution, this look pretty good. A glance at a 100% crop shows good resolution in the center of the image:

The corner, however, is not so good:

Hardly inspiring. The problem persists at 35mm. As a point of comparison, examine the next two images, the first taken with the FA 28-105 at 34mm (@ f8), the second with the dependable Pentax F 35-70 f3.5-4.5 at 35mm (@f8):

Both images look pretty good at web resolution. Now let’s examine some crops, starting with center crops:

FA 28-105, center—

F 35-70, center crop—

The FA 28-105 is sharper in the center, but not by much. Now let’s look at the corners:

FA 28-105, corner—

F 35-70, corner—

The F 35-70, a good but hardly superlative lens, is considerably sharper toward the corners. Nor does stopping the lens down improve matters. All these images were taken at f8. It’s unlikely that the problems in the corners are a consequence solely of field curvature issues. At the wide end, the FA 28-105 lens just doesn’t have much resolving power, irregardless of aperture. Fortunately, the corners improve as one zooms away from the wide end of the lens. Consider the following image, taken at 50mm, f8:

Now let’s examine the center:

Pretty good in the center at least. What about the corners? Let’s take a look:

Here we find a big improvement over what we found at the wide end of the lens. I haven’t run any exhaustive tests and can’t say precisely where the improvement begins and how rapid it is, but I would say that improvement begins to be noticeable around 43mm and reaches its nadir at 50mm. At 70mm, resolution in the far corners takes a slight hit, though it is still a lot better than it is at 35mm and wider:

70mm, f8—



Resolution in general begins to wane ever so slightly as you go much beyond 70mm, as illustrated in this pic taken at 85mm (@f8):

And the 100% crop:

Despite the slight loss of resolution on the long end of the lens, image quality is still very good at 105mm:



And one more example at 105mm, this time a landscape shot:


Keep in mind that all these images are from an APS-C DSLR (i.e, the Pentax K-5). Corner resolution is bound to be worse on 35mm film or on a so-called “full frame” censor. But other than the border to border sharpness on the wide end of the lens (e.g., 28mm to ~45mm) and the far corners elsewhere, the FA 28-105 f3.2-4.5 lens features pretty good resolution. While it doesn’t quite match what a prime lens in a comparable range could achieve, stopped down to f8 or so, it can hold its own with all but the very best Pentax zoom lenses. In the current line-up, only the DA* 50-135 and the DA* 60-250 will clearly out-resolve this lens between 50mm and 105mm.

There is, to be sure, a great deal more to a lens than mere resolution. How does the FA 28-105 f3.2-4.5 fare in regards to contrast, color rendition, and overall rendering? Quite well in point of fact. The lens was one of the first zooms to feature Pentax’s newest coating technologies, the so-called ghostless coatings, designed to reduce flare and ghosting while improving contrast and color rendition. Probably the chief merit of the FA 28-105 is its outstanding color rendition. Colors are bright, vivid, and arresting:

Although the ghostless coatings help create impressive color rendition, don’t expect miracles as far as flare control: this is, after all, a lens with 12 groups of elements. Flare will happen if you point the lens at the sun:

Build quality of the lens is not particularly good. This is mostly plastic lens, with metal mount and a few metal parts on the inside of the lens, but nearly all plastic on the outside. This is not a lens built for the ages. At some point, it probably will come apart at the seams. On the plus side, it’s small and light, compressing to just two and a half inches at the wide end of the lens and weighing just under 9 ounces. The lens takes 58mm filters and easily fits into a pocket.

One potential problem to watch out for involves the auto-focus capabilities of this lens. Some users have reported widespread inaccuracy in focusing the lens, particularly on the long end. I have experienced this myself with my lens. In fact, I would call this lens the worst auto-focusing piece of glass I have ever used. I can’t comment on its wide-open performance precisely because I can’t get it to focus accurately in those situations where its appropriate to open the lens up. Outdoors shooting landscapes I have no problems using autofocus. But then I’m shooting at f8 in bright light. Indoors matters stand otherwise. I took about twenty shots indoors with flash, and only one came in focus, the following image taken at 105mm, f4.5:

The 100% crop suggests that resolution is not great wide open (although given the focus problems, room must be left for doubt):

In any case, I would doubt you would find in a lens of this class stunning or even very good wide open performance. This is a lens best fit to use at f8. It works well as a landscape lens, as long as you remember the resolution issues toward the borders at the wide end of the lens.

More photos:

At 28mm—

At 50mm—

At 60mm—