Pentax 50mm F1.4 comparison: M, FA and DFA

User report

Comparing the M, FA and D FA versions of the Pentax 50mm F1.4 shows just how much things can change over the course of a few decades. Note that the D FA*  50mm already has its own in-depth review.

The M 50mm is a purely mechanical object. The lens feels like a solid block of metal, with no electronics at all. Focusing and aperture control are fully manual. Even after 40 years, our test copy operates smoothly, the rubber of the focusing ring is still intact and the paint in the engraved markings has not faded. How the lens was used certainly influences its cosmetics after four decades, but in the right hands the M 50mm supports the assertion that camera bodies come and go, but lenses last a lifetime. As with most M lenses, it sports a silver ring close to the front, white lettering around the front glass element, a textured focus ring. The texture is made of "pyramids" which are also found on newer lenses, however they are much larger on M lenses. The engraved focus distance scale is revealed by a cutout on the lens body.

The FA 50mm shares some similarities with the M 50mm but also includes many different elements. Apart from the metal lens mount, the body is fully made of plastic. While it certainly does not feel cheap, it pales when compared with its older sibling. It includes two features that have become invaluable to modern photographers (and taken for granted by almost all): autofocus and automatic exposure. A screw-drive mechanism operates the autofocus, generating some high-pitched noise. The lens features an aperture ring, whose operation is not as fluid as on the older lens, but which does bear the A setting which lets the camera take control.

The FA 50mm has another perk hidden inside: electronic communication, including MTF tables to be used with modern camera program lines, as well as optical performances figures which can be used for lens correction.

The D FA* 50mm is, as can be expected, a different beast altogether. Its size dwarfs the other two lenses, at five times the weight and three times the length. Mounting the hood makes the D FA* 6.5cm longer still. The newer lens offers a full metal body, an external AF/MF switch, internal focus via silent SDM, all weather resistance (AW). While the two older lenses use versions of the classic Pentax SMC coatings, the D FA* uses HD coatings for better flare control, as well as Super Protect on the front element for easier cleaning and Aerobright II for improved contrast. The D FA* 50mm offers no aperture ring and no mechanical aperture control; older cameras will not be able to control its aperture.

One last thing sets the D FA* apart: its minimum aperture is F16, a departure from the ubiquitous F22 generally offered on prime lenses.

None of the M and FA lenses shipped with a lens hood, although some were available as accessories. The D FA* ships with a large petal-shaped hood which is perfectly matched for the lens. When mounted, it sits flush with the lens, a perfect continuation of the lens body. One could be forgiven for thinking that it is a permanent staple of the D FA* 50mm.

Side by side

Looking at the front glass elements provides another perspective.

When compared side by side, the similarities and differences between the lenses become obvious. The general size is the same for the two older lenses. Weight is also comparable, with the FA being slightly lighter. Both are unobtrusive lenses, easy to handhold for long periods of time.

The D FA* is another matter. It is obvious that the lens designers received the task of delivering the best optical performances they could, size, weight (and price) notwithstanding.

In fact, the D FA* 50mm is larger than the D FA 28-105mm, the de facto consumer zoom for the K-1. Its size puts it in the same range as the D FA 24-70mm F2.8 zoom (the 50mm is almost exactly the same size, and is heavier to boot).


Handling the M and FA 50mm is, for the most part, the same experience. Both lenses are compact and light. They have almost no effect on the balance of the camera, especially a larger body like the K-1. Both lenses are easy to use over long periods of time.

Using the M 50mm requires the focal length to be set when turning on the camera, otherwise SR will not be accurate. Like with any other manual lens, the user must look at the top of the lens to set the aperture (users with good short-term memory will be able to adjust the aperture without looking since each half-stop locks with an obvious click). The distance scale is visible behind a cutout and is easy to read.

The FA 50mm's handling is even simpler. In most cases, users will set the aperture ring to A and control the aperture via the camera. Said aperture ring feels cheaper than the one on the M lens. Its movement is not as fluid and there is a plasticky feel to it. The distance scale, on the other hand, is excellent. Located behind a window, the dark print over an off-white surface is easy to read and elegant.

The size of the D FA* again sets it aside. Using the K-1 and lens combo one-handed is certainly possible, but not ideal as the lens is somewhat front-heavy. Two-handed operation is best. The lens offers no aperture ring (consistent will all modern Pentax lenses). The AF/MF switch is logically positioned on the left side, again similar to other STAR lenses. When using two-handed the D FA* 50mm is easy to use, however its weight means that it can tire the user after a while (its weight is comparable to that of the DA* 60-250mm F4 or DA* 300mm F4, and much heavier than the DA* 50-135 F2.8). In other words, the D FA* 50mm F1.4 is currently the largest Pentax prime below 200mm, a complete opposite to the pancake lenses which are part of the company's legacy.


Manual focus

Manual focusing with the M lens is a pleasure. Even after four decades, the focus ring operates smoothly, with no unwanted friction. The dampening is superb, the throw is long at 180° and the ring is wide considering the size of the lens. Users accustomed to older, manual focus lenses will feel right at home with the M 50mm.

The FA lens's ring is easy to find, being placed at the front of the lens. Its rubbery texture makes it easy to grip. However, the praise stops there. The focus ring is lifeless, as was often the case with film-era AF lenses. The throw is long, at approximately 145°.

Both lenses get longer as the focus points gets closer to the camera.

The D FA* lens offers everything one could wish for regarding manual focus. The focus ring is very wide, nicely textured (closer to the M lens than to the FA). The throw is about 125°. The ring's dampening is excellent and it will not move by accident. Nor does the ring rotate when AF is engaged; only the distance scale moves. The focus ring comes at soft stops at both ends, meaning that once the ring reaches an extreme of its range, it continues to rotate with increased friction. The D FA* also offers quick-shift, for manual AF override at any time. Finally, the lens features an AF/MF switch. Focusing is internal; the lens doesn't change its length when focusing.


There is of course no autofocus on the M 50mm. On the FA, autofocus is fast and generally reliable. It produces a medium level of noise, kept under control by the light weight of the optical elements. The lens uses screw-drive. As such, focusing using live view can feel slower, especially under low light levels. The lens does not tend to hunt, however, even using live view.

The D FA* 50mm is again in another category. Its SDM system feels extremely responsive and dependable. The lens feels among the fastest we have ever tested, and this observation holds both using the viewfinder and live view. It moves to the focus point with a speed and accuracy that's impressive. Its AF system is virtually silent.

AF Speed

The following chart presents the AF speed of both the FA and D FA* lenses, using phase detection (viewfinder) and contrast detection (live view) in varying light levels.

We tested the AF speed with a Pentax K-1. The subject was a black cross on a white background, about 1.5 meters in front of the camera. We used the central focus point. We set the lens at infinity before each test, and three measurements were averaged for each data point. Measurements were performed by recording the AF noise, at various levels of ambient light.

For reference, the Pentax K-1's autofocus sensor is rated for ambient light levels as low as -3 EV.

The FA 50mm is a pleasant surprise when using live view. It is rare to see an older, screw-drive lens reaching such speeds. It actually compares well with the D FA* 50mm. With the viewfinder the results aren't as good: the lens is quite slow in low light, although it does reach acceptable speeds as the light level increases.

In contrast, the D FA* 50mm reaches speeds rarely seen on a Pentax camera. Live view is consistently faster than viewfinder AF, but both reach very high speeds at higher light levels. Using live view consistently produces AF speeds below 0.7 seconds. When ambient light reaches around 5 EV, the lens requires less than 0.4 seconds to lock focus.


The following images illustrate how the three tested lenses are able to handle point light sources in low light conditions.

F2.8 F8
M 50mm
FA 50mm
D FA* 50mm

Both the M and FA lenses create beautiful starbursts. The M arguably offers the best results, but the two lenses are close. Even at F2.8 the starbursts are acceptable, and become well-shaped and clearly defined at F8. The D FA* 50mm does not produce results as pleasing: there is little to see at F2.8, but a decent startburst, made of many rays, appears at F8.


The progression between the fully manual M lens, the film-era autofocus FA lens, and the new, completely redesigned D FA* lens is interesting.

The two older lenses are close in size, weight and handling. Both are dwarfed by the D FA. Both create beautiful starbursts. The M's manual focus is superb, while the FA's is lacking. The D FA* is both faster than the FA for autofocus, and close to the M for manual focus. Its large size makes it harder to forget when mounted on camera.

The following pages will show if the large size of the D FA* leads to the expected improvements in optical performances. PentaxForums +Pentax Forums @PentaxForums News | Reviews | Forum

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