DA 560mm F5.6 - is it a Full-frame lens?

By PF Staff in Articles and Tips on Feb 16, 2013

As you already know if you checked our blog earlier this week, we've been fortunate enough to receive one of the first production copies of the new Pentax 560mm super-telephoto lens, and we've been very busy evaluating it for some days now! The first major test we performed was to find out if this lens truly is an APS-C lens, or if it might cover the 24x36mm full-frame format.

So, we mounted the lens on our trusted MZ-S film SLR, took some shots and patiently waited for the lab to develop the film (yes, you're right, the illustration above shows the lens with our K-5 IIs, not the MZ-S. Trust us, the test shots below were made with the MZ-S!).

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We traditionally shoot the sky to illustrate vignetting. The sky shot taken at F5.6 does not look particularly good, but if you stop down to F8 the result is acceptable and not any worse than what many lenses designed for full frame would produce. At F11 the vignetting is practically gone. The "real-life" shots below look fine at all apertures.

We measured the following light fall-off in the sky photos:

Corner light fall-off in EV (F-stops)
F5.6 1.3
F8 0.6
F11 0.12

Note the red dot on the F5.6 sky photo below - that's the spot we decided to call "corner" and that's where we took the measurement for corner value (you may have to open a larger version of the image by clicking on the thumbnail in order to see the dot).

The images were shot without the hood extended, but we got the same results shooting with the hood.

Thus, our conclusion is that the DA 560mm lens cannot be labeled as a full-frame lens. The corners at F5.6 become too dark (w/ 1.3 stops of underexposure), but overall the lens will do just fine on a 24x36mm camera at F8 or smaller, and perhaps even wide open, depending on the subject.

F5.6
F8
F11

Click the thumbnails to browse larger versions

It would have been interesting to also test the corner resolution. Unfortunately, in the interest of time we used a local lab and the resolution of the scanned negatives is too low to allow for anything but a cursory impression of resolution.

We focused on the roof right in center of the frame in the images above and the roof at F11 looks good all the way to the edge.

Here are a few more of our test shots. We have made the original images available as scanned by the lab. The images are from two different rolls and processed by two different labs, so the resolution of the scans differs. The palm tree is rendered beautifully, with nice contrast and resolution. In the images to the right we focused on the palm stem near the left edge. We actually had no difficulty with manual focus on the MZ-S with this lens.

F5.6, original scan (1.2 MB) F5.6, original scan (800 KB)
F8, original scan (1.2 MB) F8, original scan (800 KB)
F11, original scan (1.2 MB) F11, original scan (800 KB)

 

While we find it to be a shame that Pentax didn't go the extra mile and optimize this lens for potential full-frame use, the compatibility isn't quite necessary given the fact that the current Pentax DSLR lineup is comprised exclusively of APS-C cameras.  We do fear that because of this, however, those interested in full-frame bodies in the future may instead opt for the Sigma 500mm F4.5, if not a different camera system altogether.

Another key selling point of this lens is its handling (the lens can in fact be hand-held in the field due to its uniform weight distribution), so we plan on testing that next.  Stay tuned for our in-depth review for the handling test and more!

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