Pentax 40mm f/2.8 Limited SMC P-DA

Lens Reviews / Pentax Lenses i Lab tested
40mm $397
average price
image of Pentax 40mm f/2.8 Limited SMC P-DA

Lab Test Results

  • Blur
  • Chromatic Aberration
  • Vignetting
  • Geometric Distortion

(From Pentax lens literature) The SMC P-DA 40mm ƒ/2.8 Limited lens is designed for use with digital cameras. At only 15mm thick it is exceedingly thin. This exclusive "Limited Lens" assures exceptional image quality, with high contrast, high resolution, great sense of depth, and minimal aberrations. Sophisticated and portable it offers a natural perspective close to the naked eye. The SMC P-DA 40mm ƒ/2.8 Limited is an ideal standard lens that performs superbly. Like all Pentax lenses, this lens is treated with the acclaimed SMC coating for maximum light transmission, sharp definition, and high contrast images.

The 40mm ƒ/2.8 SMC P-DA limited edition is a fixed-focal length ''pancake'' lens, one of the smallest lenses to bear that moniker, and probably the smallest that Pentax produces. A pancake lens is typically constructed with the fewest number of lens elements possible, and in this case the 40mm is no exception, with just 5 lens elements in four groups.

Pentax 40mm f/2.8: lens cap, filter-mount shroud and lens.
The lens weighs just 90gm (3.2 oz), and is described by Pentax as being designed for use with digital cameras. We mounted the 40mm ƒ/2.8 on a Pentax film body, and could find no evidence of vignetting. However, our film body doesn't have aperture control, which would make it hard to use effectively as the 40mm ƒ/2.8 isn't equipped with an aperture ring. The lens takes both 30.5mm and 49mm filters in an interesting lens cap/hood design, and is available now for around $250.

Our review sample of the 40mm ƒ/2.8 seemed to be slightly sharper on the left side than the right, but only marginally so. It would probably be hard to distinguish this difference, as the difference is about one blur unit.

Overall, the 40mm ƒ/2.8 is a very sharp lens, never exceeding three blur units and averaging around 1.5. Set to apertures less than ƒ/8, some corner softness is visible, surprisingly most at ƒ/5.6, where the right side of the frame approaches three blur units, but the center stays sharp as sharp as we can detect at one unit. The lens performs better at ƒ/2.8 and ƒ/4, where is corner softness is visible, but less significant. At ƒ/8 the lens is sharp but for a very slight blur on the right side, and by ƒ/11 it's tack-sharp across the entire frame. At ƒ/16, the effects of diffraction limiting set in slightly - in the form of 1.5 blur units across the entire frame, and hitting 2 units by ƒ/22. With an exceptional observation that is almost perceptually insignificant at ƒ/5.6, we see excellent performance for sharpness with this lens.

Chromatic Aberration
There is virtually no chromatic aberration visible in testing the 40mm ƒ/2.8. Chromatic aberration is almost non-existent with the lens set to its widest aperture, and increases a negligible amount as the aperture is stopped down. We're talking less than 2/100ths of a percent of frame height on average, and not exceeding 3/100ths in the corners - this is outstanding performance.

Shading (''Vignetting'')
The 40mm ƒ/2.8 does vignette very slightly at ƒ/2.8, showing almost a half-stop of shading in the corners. This improves at ƒ/4, and reaches its average and imperceptible level of a quarter-stop of corner shading at ƒ/5.6 and smaller.

Being a prime lens with a fixed focal length, distortion is also fixed. In the case of the 40mm ƒ/2.8, this distortion is fixed at an imperceptible 0.1% barrel distortion on average, and 0.25% in the extreme corner regions.

Autofocus Operation

Pentax 40mm f/2.8 with standard AA battery for scale.
The 40mm ƒ/2.8 autofocuses very quickly. It's mechanically driven, so it does make a noisy whine when focusing. On a K100D Super, it racks through the entire focus range in approximately one second. Point-to-point focusing is very quick, probably because there are very few lens elements to push around, and is slightly less noisy.

The lens isn't rated for macro, and this shows in its macro specifications: 0.13x maximum magnification, with a close-focus distance of 40cm (just over fifteen inches). There are better macro choices.

Build Quality and Handling
Let's get this out of the way right up front - the 40mm ƒ/2.8 is small. When attached to our Pentax K100D Super, the front of the lens was flush with the pop-up flash and only a half-inch longer than the grip. This camera and lens combination is ultimately portable - it easily fit into my coat pocket, and given the lens' 40mm focal length, it was a very usable, walk-around choice. With its black finish and all-metal construction, the 40mm is tougher than it looks.

Did we mention it's small?
So, it's small. So small, in fact, that when mounted on a camera, you can't easily see its only feature - a distance scale, etched onto the focus ring - without moving either yourself or the camera. Pentax has used its ''quick-shift'' focus system in the 40mm pancake, so you can override autofocus and focus manually any time you like by just turning the focus ring. The ring has good texture, and the focus range is stops solidly at either end. The full focus range is a forty-five degree turn of the focus ring. In practice, I found the lens to be very quick and responsive, and it produced very nice images.

However, if there was a ''gotcha'' with this lens, it has to be its choice of combination lens hood and cover. Either one is a bit of pain to remove, as they need to be screwed on or off. Given its miniscule size, the lens doesn't need much of a lens hood, so Pentax has designed a combination hood/cover, which is more of a shroud than a hood. The useful part of this front cover is that you can either remove the small circular insert and use the lens with the shroud, or remove the whole lens hood and attach 49mm filters. The front of the lens doesn't rotate during focusing, as you would expect, so polarizing filters will stay where you need them to. The small insert is 30.5mm in diameter, and yes, you can use 30.5mm filters on this opening. If I used this lens more often, I could see losing the small cover in my couch cushions.

It just so happens that the lens cap for the 21mm ƒ/3.2, a slide-on model with black felt lining, fits properly on the 40mm ƒ/2.8. It's much easier to attach and remove.


Pentax 43mm ƒ/1.9 Limited SMC P-FA ~$470
A slightly more up-market and exotic lens, both in style and focal length, the 43mm ƒ/1.9 showed slightly more chromatic aberration and wasn't as sharp, but still showed remarkable results in our testing. It's a full stop faster, but not as small as the 40mm; it has a much better lens hood, and is more backward-compatible with older film bodies, being equipped with an aperture ring.

Pentax 50mm ƒ/1.4 SMC P-FA ~$200
We haven't tested the Pentax 50mm. It's a full frame lens with an aperture ring which takes 49mm filters. It weighs more, costs less, and is a full two stops faster.

Pentax 35mm ƒ/2.8 Macro Limited SMC DA ~$440
We haven't tested the Pentax 35mm. Its specifications list it as a reduced-frame lens, designed for macro use. It's larger, weighs more, but has a slightly wider field of view, and the same aperture settings.

Sigma 50mm ƒ/2.8 EX DG Macro ~$230
Slightly more telephoto but just as fast, the Sigma 50mm ƒ/2.8 macro produces consistently sharper results, but they have slightly more evidence of chromatic aberration. With virtually no evidence of vignetting, 0% distortion, and macro capability to boot, this lens is an excellent alternative to the pancake; of course, it's nowhere near as small.

I quite liked using the 40mm ƒ/2.8 Limited edition, and its optical performance is one of the better examples of Pentax's declarations of quality they apply to its limited edition of lenses. Once I found I could use the lens hood from the 21mm ƒ/3.2 prime, I found it much more convenient to use as a walkaround lens; having to screw on and off the hood was a real frustration. So with that one caveat, the 40mm ƒ/2.8 is an excellent lens, and a worth setting aside the very small amount of space it will require in your camera bag.

Sample Photos

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.

Pentax 40mm f/2.8 Limited SMC P-DA User Reviews

9.8/10 average of 8 review(s) Build Quality 9.9/10 Image Quality 9.5/10
  • 9 out of 10 points and recommended by dugong5pm (52 reviews)
    razor sharp, lightweight, tiny!
    pricey, hard to find

    one of Pentax's jewel (along with the other "Limited"). superb performance & also stylish. Use it with the tiny K-x/K-r, and you're ready for streets. Colors are great & amazing sharpness. a must have lens for pentax users.

    reviewed October 12th, 2012 (purchased for $450)
  • 10 out of 10 points and recommended by sjwaldron (6 reviews)
    Small convenient lens with great build quality and image sharpness.
    The manual focus ring is almost too small.

    What I like about the lens:
    - A great all-rounder type lens that’s almost at the standard focal length for APS-C sized image sensors (35mm would be equivalent).
    - A lens that’s frankly special and unique due to how physically convenient it is yet still achieves no compromises image quality.
    - Small portable size, probably one of the smallest 35mm lenses available.
    - Easily carry the lens with you in a pocket or similar (comes with a soft leather bag). Even if you are a photographer that prefers zoom lenses, also having this lens with you at all times should be a given. Just make sure your bag is big enough to hold that zoom after you become smitten with the 40mm.
    - A sharp high contrast lens from its widest aperture. Edge to edge sharpness abound.
    - Bokeh quality is exceptional thanks to the large number of aperture blades.
    - “good enough” for 35mm full-frame sensor if a FF-DSLR is ever released by Pentax.
    - High all metal build quality and dependable auto-focus method (screw-drive) you can depend on as a life-long lens.
    - Lens specifications and serial number engraved on the lens.
    - Quick-shift manual focus is useful as always. It’s useful to me when I’m done using the lens and then I manually rotate the lens back to it’s smallest size before putting it back into the camera bag.
    - The lens doesn’t have any issues with flare or chromatic aberrations.

    What I’m not too fond of:
    - The manual focus ring is almost too small.
    - I somehow got a small scuff on my manual focus ring, showing a tiny bit of silver aluminum. Not sure how it happened, but don’t expect the lens to stay completely black unless you baby it (I don’t baby my equipment by any means).
    - Screw drive auto-focus, while reliable, is louder than in-lens SDM motors. Not really a negative given the positives of screw drive, unless you really need something low noise.
    - The lens hood and lens cap, while convenient in some ways, takes a few seconds to attach and remove as they are screw thread type devices.
    - 40mm focal length isn’t optimal on APS-C cameras. When photographing people at events, it’s primarily best for waist and up style images instead of full body ones. A Pentax 31mm Limited lens in this respect is a better buy if you can afford one.
    - Not specifically designed to be weather resistant (WR), but those are a newer addition to Pentax’s lens lineup.
    - I would like to see nice especially curved aperture blades like the D-FA 100mm WR Macro lens has, but the sheer number of blades the 40mm LTD has compensates for that.

    Part of the challenge of DSLR photography is finding the motivation to take equipment out as sometimes the stuff can be burdensome compared to say a digicam in your pocket. I take this lens out by itself attached to the K-7 all of the time as it’s just that convenient. Get a camera bag that can hold just that combination and you have a high quality, fully optical (viewfinder, etc) system that’s ready at a moments notice without much baggage holding you down. Pentaxians are doing a disservice to themselves if they don’t have a copy of this lens. No lenses are prefect, including this one, but it does many things right. It gives you a good deal of convenience and mobility, yet also gives you strong performance at a reasonably useful focal-length.

    More information and pictures on my blog.

    reviewed December 8th, 2010 (purchased for $340)
  • 10 out of 10 points and recommended by Tord (30 reviews)
    Small, sharp and compact
    None that I can think of!

    Amazing little lens which was my introduction to Pentax Limited range, and it is really a petite wonder!

    Some have problems with the lens cap, but I drilled a small hole in mine and secure it with a string to the lens barrel - works OK, and no risk of losing it!

    A good allround lens, and very tiny!

    reviewed September 5th, 2010
  • 10 out of 10 points and recommended by RadiantLite (16 reviews)
    tiny, great image quality

    Pentax 40mm f/2.8 limited is an exotic lens which can produce a really nice image quality even wide open at f/2.8. Physically, it is very small and thin even with the lens hood attached. (When you buy this lens you will get the lens hood and also nice small leather pouch). It can focus pretty close 30cm to infinity. When you focus in, the lens will rotate and protrude around 1/2 inch. At around 165g, this lens is very light, basically you'll feel like you are only carrying a camera without lens, which is good for portability.

    Check out
    for sample photo and reviews

    reviewed June 13th, 2009 (purchased for $300)
  • 10 out of 10 points and recommended by tachyon1701 (8 reviews)
    Tack sharp, very quick AF, small size, light weight, build quality

    This is a true gem in the Pentax's already amazing prime lineup. I mean pancakes are what Pentaxs are known for! Every pentax owner should have one of these in their camera bag. It won't take up a lot of space, i promise!

    From image quality, to build quality, from AF speed, to chromatic aberration control, everything is top notch. People complain that the lens doesnt have a bigger aperture, or the lens cap is too fiddly (it's not, you can always use a generic 49mm lens cap if you don't like the screw-on one), but they don't realise what we are getting for the price!

    Images can't get any sharper, even at f2.8! People pay $1000 for primes and can't get IQ like this! This is a bargain too good to pass up!

    It is also worth noting that a 50mm "normal" prime isn't really normal at all. Just google or wiki it, and you'll find out that the true normal focal length is 43mm.

    reviewed September 14th, 2008 (purchased for $300)
  • 9 out of 10 points and recommended by grim grimsson (6 reviews)
    Sharp, lightweight, fast

    A lens that is fun to use. It is lightweight, I can really feel the difference from other lenses I have when carrying the camera around. It can fit in the pocket as an extra lens without carrying a bag for the equipment.

    It is fast, and sharp all the way to the border from wide open. Colours are rendered well.

    Very solid construction.

    reviewed June 30th, 2008 (purchased for $300)
  • 10 out of 10 points and recommended by nighthunter64 (5 reviews)
    Smallest lens ive used !!
    none so far

    this is the smallest lens in the world and its quality is top notch !!!

    super good light with big opening!!

    - Superb Pictures
    - The lightest lens around for 40mm
    - big opening f2.8

    Perfect Portrait lens.. easy to carry...

    The new Pentax Limited series is a must for everyone owning Pentax DSLR equipement!!

    reviewed January 12th, 2007 (purchased for $274)
  • 10 out of 10 points and recommended by leprechaun (7 reviews)
    Gives me the ultimate: an SLR in my pocket

    I bought a used DS body so that I could use their stunning ultrawide/fisheye zoom. Then I saw this "pancake" lens.

    It took all of two minutes to make up my mind (one of which was purely $$ related). I have no regrets.

    Camera and lens fit in a coat pocket. Bought a belt holster case for the pair so I could leave the jackets and coats at home.

    What I have is DSLR that goes anywhere anytime on my hip. It's a treasure.

    The lens is plenty sharp, and fast enough to cope with many situations.

    You may still want a good pocket subcompact, but a DSLR on your hip is addicting. Take my word for it. If you own a Pentax, take a look.

    reviewed January 7th, 2007 (purchased for $375)