John Riley reviews the premium full-frame HD 21mm f/2.4 Limited lens from Pentax. How does this beautiful lens measure up, John shares MTF & CA Charts, along with sample photos and his verdict.
Posted: 25/11/2024 - 10:31
Handling and Features
Performance
Verdict
Specification
Introduced in 2021, the HD Pentax-D FA 21mm f/2.4 Limited DC WR lens is a full frame ultra-wide optic, designed for use with the K-1 and K-1 II full frame DSLRs. When used on a crop sensor camera, the "35mm equivalent" field of view would be 31.5mm, often described as a "wide standard" lens. It has the "Limited" designation and we accordingly expect the highest standards, as it joins a distinct and highly desirable group of Pentax optics. Armed with the 36MP Pentax K-1 full frame DSLR, let's have a close look at this, one of the most recent lenses from Pentax, and check out how it performs technically and how it handles out in the field.
HD Pentax-D FA 21mm f/2.4 ED Limited Handling and Features
A Limited lens is always a pleasure to handle, with its machined Aluminium body, fine engravings and beautifully smooth controls. There are black and silver versions, the silver one being anodised, not simply painted.
Starting at the front of the lens, the petal lenshood is fixed, but there is still a standard 67mm filter thread. A special mention should be made of the splendid metal lens caps that are supplied with the Limited lenses, with their green baize interiors. They slide smoothly over the lens, sit firmly in place and are a lesson in how a lower cost item well designed can actually out perform some of the most expensive lenses in the marketplace.
The overall impression is of solid quality, reasonably compact and weighing in at just 418g, as measured. Dimensions are 74mm x 89mm and these are constant as we focus as IF (Internal Focus) does not alter the length of the lens. The focusing action is fast and virtually silent, using a DC motor. The manual focus ring is electronic and ultra-smooth in operation. It is perhaps a bit on the light side, but it does mean that the motor can shift the ring easily, as it does rotate with AF. The distance scale is in the traditional Pentax cut-out and a depth of field scale is provided. The focusing ring has hard stops at both ends of the range, and extends beyond infinity to allow for expansion and contraction of the lens components.
Closest focus is 18cm, or 0.59 feet. This equates to a distance of just 7cm from the front element to the subject, so the lens can focus pretty close. Maximum magnification is 0.26x, closer than the norm for such lenses. Quick Shift is available, so the focus position can be tweaked manually whilst using AF.
Optical construction is 11 elements in 8 groups, including 4 ED (Extra-low Dispersion) and 1 Super ED. Pentax also offer more information about the front group of elements, which they say include a large aperture negative meniscus element, biconvex aspherical glass moulded element and HR (High Refractive) element. The electomagnetic diaphragm consists of 8 rounded blades. The mount is KAF4 compliant to support this, so the following cameras are compatible, those indicated with a star needing the latest firmware upgrade: K-1 II, K-1*, K-3 III, K-3 II*, K-3*, KP, KF, K-70, K-S2*, K-S1*, K-50*.
The latest HD coatings are used, and the front element has the SP (Super Protect) coating to help repel moisture, dirt and grease. The lens as a whole is Weather Resistant.
HD PENTAX-D FA 21mm f/2.4 ED Limited DC WR Sample Photos
Pentax Users will be fully familiar with the operation of this lens, which has few controls and is very easy to use and equally easy to like. Results can be as dramatic as any ultra-wide, without being so wide as to make composition challenging. As our photographic tastes have developed over the years, people in general are more and more used to wider shots. Using the lens is a great experience, especially when it is so delightfully made and has such a feel of quality.
HD Pentax-D FA 21mm f/2.4 ED Limited Performance
Central sharpness is very good from f/2.4 all the way through to f/16 and is still good at f/22. The edges start off as fair at f/2.4 and good at f/2.8 and f/4, rising to very good from f/5.6 to f/11 and remaining good at f/16 and f/22.
HD PENTAX-D FA 21mm f/2.4 ED Limited DC WR MTF Charts
How to read our MTF charts
The blue column represents readings from the centre of the picture frame at the various apertures and the green is from the edges.
The scale on the left side is an indication of actual image resolution and sharpness as LW/PH and is described in detail above. The taller the column, the better the lens performance.
For this review, the lens was tested on a Pentax K-1 using Imatest.
Central sharpness is very good from f/2.4 all the way through to f/16 and is still good at f/22. The edges start off as fair at f/2.4 and good at f/2.8 and f/4, rising to very good from f/5.6 to f/11 and remaining good at f/16 and f/22.
Central CA is very well corrected. There is some CA at the edges, but for most shots this goes unnoticed. In severe subjects, such as branches against bright sky, there may well be visible fringing and if this is a problem then there are software solutions.
HD PENTAX-D FA 21mm f/2.4 ED Limited DC WR Chromatic Aberration Charts
How to read our CA charts
Chromatic aberration (CA) is the lens' inability to focus on the sensor or film all colours of visible light at the same point. Severe chromatic aberration gives a noticeable fringing or a halo effect around sharp edges within the picture. It can be cured in software.
Apochromatic lenses have special lens elements (aspheric, extra-low dispersion etc) to minimize the problem, hence they usually cost more.
For this review, the lens was tested on a Pentax K-1 using Imatest.
Distortion measures -0.87% barrel, which is very modest for an ultra-wide lens.
Bokeh is the smoothness of the out of focus areas in an image and the lens delivers some very pleasing results.
HD PENTAX-D FA 21mm f/2.4 ED Limited DC WR Aperture Range
Ultra-wide lenses are difficult to shield from flare inducing light, so it is good to see that this lens is highly resistant. Even with light sources right in the frame, there is no sign of flare and there are no artefacts. An excellent performance.
Vignetting is present, but at acceptable levels.
| Aperture | Vignetting |
| f/2.4 | -1.7 |
| f/2.8 | -1.6 |
| f/4 | -1.3 |
| f/5.6 | -1.2 |
| f/8 | -1.2 |
| f/11 | -1.1 |
| f/16 | -1.1 |
| f/22 | -1.1 |
Value for Money
The HD Pentax-D FA 21mm f/2.4 ED Limited DC WR lens is priced at £1349.00 and unfortunately there are no obvious examples of alternatives. Taken in isolation then, we do seem to get quite a bit of technology in there for a not unreasonable price. From time to time there are offers on Pentax lenses, so judging the time to buy could reduce that cost significantly.
There are of course older lenses that cover the 20mm-mark, such as:
- SMC Pentax-FA 20-35mm f/4
- SMC Pentax-FA 20mm f/2.8
These may be found on eBay and other second hand sellers and can be quite resonably priced. They will not have weather sealing, nor will they have QuickShift, but will be capable of excellent results.
HD Pentax-D FA 21mm f/2.4 ED Limited Verdict
Something we have said for a long time is that figures and tests are not the be all and end all of a lens's worth, and Pentax say the same on their website when they discuss the merits of this 21mm lens. The sharpness figures are very good and very consistent in the centre, dropping off at the edges, but then 21mm lenses are not really intended to shoot flat test charts at the close distances involved. The actual visual impression out in the field is much crisper and sharper than the figures suggest. The edges do fall off, but it is possible that there is some field curvature at close distances as results at longer distances look much better. In any event, even this can support bokeh effects and enhance the diffusion from the central, sharp core of the image. The end result is a very pleasing overall effect, something that the Limited lenses have in common, the magic ingredient that makes a good lens great.
The 21mm f/2.4 is an elegant, well made lens that delivers lovely results and it is therefore Highly Recommended.
HD Pentax-D FA 21mm f/2.4 ED Limited Pros
- Sharp, crisp images
- Low central CA
- Excellent flare resistance
- Modest vignetting when stopped down
- Precision manufacturing standard
- Moderate barrel distortion
- Quick Shift
- Weather Resistance
HD Pentax-D FA 21mm f/2.4 ED Limited Cons
- Some edge CA
- Noticeable vignetting at wide apertures
Specifications: HD PENTAX-D FA 21mm f/2.4 ED Limited DC WR |
||||
| General | ||||
| Focal Type | Wide | |||
| Lens Mounts | Pentax K HD-D FA | |||
| Availability | ||||
| Year announced | 2021 | |||
| Discontinued | No | |||
| Dimensions | ||||
| Diameter | 74mm | |||
| Height | 89mm | |||
| Weight | 416g | |||
| Construction | ||||
| Weather-sealed | Yes | |||
| Groups | 8 | |||
| Elements | 11 | |||
| Blades | 8 | |||
| Lens | ||||
| Maximum magnification | 0.26x | |||
| Internal focusing | Yes | |||
| 35mm equivalent | 21mm | |||
| Stabilised | No | |||
| Filter Size | 67mm | |||
| Min Aperture | f/22 | |||
| Max Aperture | f/2.4 | |||
| Angle of View | 92 - 81° | |||
| Focal Length | 21mm | |||
| Focusing | ||||
| Min Focus | 18cm | |||
| Focusing Type | Automatic, Manual | |||
Members gallery photos using: HD PENTAX-D FA 21mm F2.4 Limited
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