Pentax 70mm f/2.4 Limited DA HD
Lab Test Results
April 4, 2014
by William Brawley
Not an altogether new lens, the Pentax 70mm ƒ/2.4 Limited DA HD is a member of Pentax's newly-refreshed Limited series of lenses that now feature their "High Definition" lens coating. Featuring practically identical specs to the previous Pentax 70mm ƒ/2.4 Limited SMC DA lens, the new "HD" model replaces the Super Multi Coating with this new HD coating, which claims to better control ghosting and flares as well as improved color balance. It's also supposedly more durable thanks to higher packing density and a stronger bond between the coating materials (although, we'll take Pentax's word for it on this last point -- we're not going to scrape up the front element to check).
The construction and optical formula for the Pentax 70mm HD Limited lens remains unchanged from the previous model, although Pentax has tweaked the aperture diaphragm for a rounder shape, which should make for more pleasing bokeh. Cosmetically speaking, things are not drastically different from the older model, with the new version sporting a red ring as opposed to a green one.
The Pentax 70mm ƒ/2.4 Limited DA HD ships with front and rear caps, lens hood and a soft case and is currently available in either black or silver with a retail price around $746.95: Adorama (black, silver)| Amazon (black, silver)| B&H (black, silver).
The Pentax 70mm ƒ/2.4 HD Limited is a nice, sharp lens. Wide open, the lens produces images with nice, sharp centers, with some relatively minor corner softness. Stopping down to ƒ/4 effectively sharpens up the corners, as well as improving sharpness overall. Going down to ƒ/5.6 shows the sweet spot for this lens with very sharp images, especially in the center -- although, as our graph shows, the lens is very uniform across the frame in terms of sharpness. Once you stop down to ƒ/11 and smaller, diffraction starts to affect critical sharpness, but it's very minor overall with ƒ/22 showing it to the greatest degree, which is not surprising. Overall, a very even and sharp lens, making it an excellent short telephoto lens for portraits.
The new Pentax 70mm HD Limited lens does well at controlling chromatic aberration, although it's not the lowest CA level we've ever seen. The average amount of CA is still quite low, even wide open, and only slightly increases as you stop down (but staying under 300ths of a percent of frame height). Looking at our sample images, we saw nice center areas pretty devoid of any CA, but out in the corners at both ƒ/2.4 and ƒ/8, there's certainly noticeable CA in the form of bright purple and subtle green fringing. However, it looks to be minor enough that a quick adjustment in your photo editing software of choice should clear it up.
The Pentax 70mm lens does show vignetting at the wider apertures at a little under a half-stop of light loss in the corners at ƒ/2.4-ƒ/2.8. Stopping down to ƒ/4 dramatically reduces the appearance of vignetting to well under 0.25EV and remains constant at this level throughout the remaining apertures.
Being a medium telephoto portrait lens, you would expect to see very little distortion, and the Pentax 70mm HD Limited lens is no exception. There's only a touch of barrel distortion on average, but looking at our sample images as a whole, you can see, in fact, a hint of mild pincushion distortion, that would be either unnoticeable in real-world portait shots or easily corrected in post-processing if desired.
Despite its cool retro looks, Pentax's HD Limited series features high-tech modern lens coatings. However, something that remains decidedly old-school, at least for this 70mm lens, is the autofocus motor. There's no stealthiness about it -- bring this lens out and people will hear you coming. Due to the traditional screw-drive AF motor, the lens is far from silent with a noisy, whining sound when you autofocus. The good news is that it still focuses very quickly: well under one second from minimum to infinity focus distance. Apart from the noise, the AF feels excellent and performs very well.
Of course, there's manual focus as well, which is controlled via a switch on the camera body itself. The lens features both focus distance and depth of field markings. There is also manual focus override -- Quick-Shift Focus System in Pentax lingo -- that let's you adjust focus even after autofocusing.
This lens is not really designed for macro shooting due to its 70cm (27.5 in.) minimum focusing distance that provides only a 0.12x (1:8.3) magnification.
Build Quality and Handling
Despite being a DSLR lens, the Pentax 70mm ƒ/2.4 Limited DA HD keeps not only the retro styling of an older film SLR lens, but also the size. It's extremely compact and lightweight -- almost like a Micro Four Thirds or a pancake lens -- with a length around one inch without the lens hood. Like similarly-sized pancake lenses, the Pentax 70mm HD Limited lens looks almost comically small on a larger DSLR like the K-5 we tested it on, especially without the lens hood attached. However, it's not really about looks is it? The compact size of the 70mm, and the other HD Limited primes for that matter, make them extremely portable, which is a nice change from a typically large DSLR portrait lenses. The Canon and Nikon 85mm ƒ/1.8 lenses, for instance, are significantly larger, although, at the same time, they do have significantly brighter ƒ/1.8 apertures.
The build quality itself is excellent with an all-metal construction -- complete with laser-engraved lettering and markings -- and a nice, silky-smooth mechanical focus ring. Even the screw-on, retractable lens hood is metal with a high-quality feel. Unlike many other Pentax lenses, this HD Limited lens is not weather-sealed nor has a gasket around the mount, however it does have the Super Protect (SP) coating on the front element to repel dust, moisture and grease.
Now, in terms of coatings, the big change to this lens is the replacement of the Super Multi Coating for Pentax's new High Definition (HD) coating, which provides better control over ghosting and flares as well as improved color balance. Our news editor and reviewer Mike Tomkins -- and an avid Pentax fan -- had a chance to take this lens and the other HD Limited lenses out for a comparison. And while he only had the 21mm and 40mm non-HD versions to compare side-by-side, the results show a noticeable reduction in lens flare as well as increased contrast and saturation from the new HD Limited lenses -- the new High Definition coating definitely does its job.
See the Pentax K-3 gallery for the full-resolution images.
As for the optical formula itself, the lens has 6 elements in 5 groups, without any fancy extra-low dispersion or aspherical elements. Compared to the non-HD-coated version of this lens, the aperture diaphragm has been updated to a rounded design -- still with 9 blades -- for improved background blur.
Not surprisingly, the primary alternative is the non-HD coated Pentax 70mm ƒ/2.4 Limited SMC DA. And while we haven't tested this lens, the optical formula is identical to the new HD-coated version minus, of course, the new HD coatings and curved aperture blades. Therefore, we can guess that the optical performance in terms of sharpness, CA, distortion and vignetting would be very similar. Also, now that the HD-coated version is available, this older lens can be found -- though not as readily -- for a more affordable price (~$570).
Another option would be the Pentax 77mm ƒ/1.8 Limited SMC P-FA. This lens provides a similar portrait-style medium telephoto focal length and retro-styled all-metal design and construction, but with a significantly brighter ƒ/1.8 aperture, which explains the larger size and approximate $1,000 price tag.
While perhaps not a significant upgrade for existing Pentax 70mm ƒ/2.4 Limited SMC DA users, the new Pentax 70mm ƒ/2.4 Limited DA HD is, all in all, an excellent lens with fantastic sharpness -- especially stopped down a bit -- and well-controlled CA, distortion and vignetting. The big story is the new HD coating, which as advertised, does its job to reduce lens flare and increase contrast and saturation. Furthermore, the cool retro-styling and ultra-compact size make is an excellent, go-anywhere portrait lens. However, the only downside is the noisy, screw-drive autofocus motor, that can be quite audible, especially in quiet locations. The lens still autofocuses very quickly, just don't expect to be quiet and stealthy with this lens. Overall, the Pentax 70mm ƒ/2.4 Limited DA HD is another impressive lens in Pentax's lineup, and Pentaxians looking for a super-small, lightweight portrait lens should look no further.
Check out some sample photos shot by our senior lens technician Rob Murray. You can view more sample photos, plus download the full-resolution files, over at our Flickr page.
The VFA target should give you a good idea of sharpness in the center and corners, as well as some idea of the extent of barrel or pincushion distortion and chromatic aberration, while the Still Life subject may help in judging contrast and color. We shoot both images using the default JPEG settings and manual white balance of our test bodies, so the images should be quite consistent from lens to lens.
As appropriate, we shoot these with both full-frame and sub-frame bodies, at a range of focal lengths, and at both maximum aperture and ƒ/8. For the ''VFA'' target (the viewfinder accuracy target from Imaging Resource), we also provide sample crops from the center and upper-left corner of each shot, so you can quickly get a sense of relative sharpness, without having to download and inspect the full-res images. To avoid space limitations with the layout of our review pages, indexes to the test shots launch in separate windows.
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