Pentax FA 24-90 f3.5-4.5

The Pentax FA 24-90 was released in 2001. It was one of the very last film lenses produced by Pentax. It was rather expensive for a mostly plastic, variable aperture lens, selling, when it first came out, for over $500. There was a bit of a backlash against the lens on account of the perceived issues with its build-quality. However, despite these problems, it is generally recognized as the best variable aperture standard zoom lens made for full frame (i.e., 35mm film) cameras that Pentax ever produced. The only standard zoom lens that can boast superiority to the FA 24-90 is the FA* 28-70 f2.8, a lens that routinely sells, on the used market, for well over $1,000.

So how good is Pentax’s very best full-frame variable aperture standard lens? It’s very fine, indeed. Optically, this is the best zoom lens I have ever used. It’s better (by an admittedly small margin) to the DA 16-45 and the DA 12-24. Perhaps “better” is a bit misleading. Perhaps it would be more accurate to say that, at its best, it’s better than those other zoom lenses are at their best. When the FA 24-90 is used at its strong focal lengths and apertures, it is a stunning piece of glass. But this does not mean it’s not without some flaws and shortcomings. Let’s look at some images that show both its strengths and weaknesses. Let’s examine a shot taken at the wide end of the lens, i.e., at 24mm:

At 24mm, the lens has some issues in the corners, as the following 100% crops demonstrate. The first crop is toward the center of the image (along the bottom):

Very good resolution here, as can be readily seen. Now let’s examine the corner:

Not so good. The resolution has clearly suffered. Now consider the following image, also taken at 24mm:

Now a 100% crop of center, following by 100% crop of corner:

Now while the corner is still not tack sharp, it’s perhaps slightly better than the previous example. Why the slight difference? Very simple: focus stacking; that is to say, two images where combined, one where the focus point was at the center of the image, the second where the focus point was on the tree along the edge of the frame. What does this exercise indicate? Namely this: that there seems to be at least some field curvature issues with the lens on the wide end which is contributing to the soft corners. Field curvature is not unusual in wide angle and zoom lenses. However, the resolution issues toward the edges at the wide end of the lens can hardly be explained by field curvature alone. The lens simply does not resolve that well toward the edges at the wide end of the zoom.

Edge to edge sharpness improves as one zooms away from 24mm. Note the following image taken at 35mm, followed by a 100% corner crop:

Now compare this to the center crop:

It’s still sharper in the center, but not by much. Corner to corner resolution continues to improve toward the middle of the zoom’s range, until it begins a slight abatement toward the long end. In the middle of the zoom, the lens is magnificent: it combines excellent resolution with beautiful rendering, lens contrast, and color rendition. Here’s an image at 48mm:

And the 100% crop:

Another 48mm image:

And the 100% crop:

And an image at 52mm:

The lens maintains it’s excellent quality well into the longer focal lengths. Here’s an image taken at 73mm:

And the 100% crop:

And finally, 90mm:

100% crop:

100% crop:

I tend to think that the lens does lose just a bit of resolution at the very long end, say, in the 80 to 90 range. There is, however, another issue which makes it difficult to determine the exact amount of resolution lost. The lens does not always focus as accurately at the long end as at other ranges. I’m not sure to what degree this might be due to the camera, and what degree it is the lens’ fault; but I have taken some images at 90mm that were soft at 100% resolution, and others that had a decent amount of resolution.

So far, all the images show were taken at or near f8. I bought this lens primarily to use in landscape work, so I personally have little interest in how it performs wide-open. The few shots I’ve taken wide open suggest the following: (1) the lens is quite soft wide open at 24mm; (2) it’s better, but hardly fantastic in the middle of the zoom; (3) it’s not as good wide open at the long end of the lens as in the middle, but still better than at the wide end. I have but one sample to show, which was taken at the long end of the lens, 90mm:

100% crop:

Not bad, but not great either. This is not a lens I would purchase if shooting wide open were important to me. I believe this lens performs at its best in landscape work. Those needing a lens that performs well wide open should probably look elsewhere.

Build quality of the lens is fair to middling. It’s constructed well enough: high quality plastic around a metal mount and frame. It is an internally focusing lens; and like all Pentax non-star internal focusing lenses, the focus ring contains no dampening at all. This is not a great lens for manual focus work. If the lens has a short-coming, it’s that the zoom mechanism is poor. And this is not merely an issue of zoom creep (which can be a problem); but it just does not feel particularly sturdy or reassuring. This is true of most of the non-star FA zooms. The zoom mechanism is a bit on the loose side. There’s little if any dampening in it. Pentax greatly improved their zoom dampening in their non-professional glass in the DA line. But even a very late FA zoom like the 24-90 still suffers from the build quality issues in the zoom mechanism. In all other respects, I find the zoom lens well made. The fact that the exterior casing is entirely plastic I don’t regard as a serious issue. Other than the zoom mechanism, the build quality of the lens is on par with the DA 16-45. Pentax merely, in their DA line, put thin metal strips on the exterior of their lenses. But that is hardly a major improvement in build quality.

More samples from the FA 24-90: