{"id":13451,"date":"2020-11-23T13:31:49","date_gmt":"2020-11-23T12:31:49","guid":{"rendered":"https:\/\/phillipreeve.net\/blog\/?p=13451"},"modified":"2026-01-14T10:02:57","modified_gmt":"2026-01-14T09:02:57","slug":"review-pentax-fa-31mm-f1-8-limited","status":"publish","type":"post","link":"https:\/\/phillipreeve.net\/blog\/review-pentax-fa-31mm-f1-8-limited\/","title":{"rendered":"Guest Review: Pentax SMC FA 31mm f1.8 Limited"},"content":{"rendered":"

11\/15\/2020<\/span>:\u00a0 “Alternatives” and “Conclusion” and “Notes” sections has been updated in light of new releases, and a few more sample images have been added.<\/p>\n

The Pentax 31mm f1.8 Limited is a fast moderate wide angle lens released in 2001. It\u2019s designated as one of Pentax\u2019s \u201cLimited\u201d series, denoting its high status within the Pentax catalogue. Since its release, the 31 Ltd has been beloved, especially within the Pentax community. I picked up my first copy in pursuit of a fast, decently priced alternative to the Sony RX1<\/a>. Sony hasn’t provided shooters with a native fast 35mm f1.8 or f2 option. The 31 Ltd was a highly praised lens upon release, but optics have come along way recently, and it\u2019s getting long in the tooth. Let’s see how it holds up 17 years after it’s release, and what type of images we can expect.<\/p>\n

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\nThe 31mm focal length is an oddity, being near but noticeably different from the more conventional 28mm or 35mm focal lengths. The 31 ltd functions as versatile jack-of-trades lens with its 31 FL. The lens is still in production by Pentax\/Ricoh, coming in either silver or black.<\/p>\n

To view larger versions of the photos in this review, follow this link to my Pentax 31 ltd album on flickr<\/a>:\u00a0\"\"<\/span><\/p>\n

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Specifications<\/h1>\n\n

Before delving into the performance aspects, let\u2019s start with some relevant specifications:<\/p>\n\n\n\n\n\n\n\n\n\n\n
Filter Size:<\/td>\n58mm<\/td>\n<\/tr>\n
Mount:<\/td>\nK-mount<\/td>\n<\/tr>\n
Weight:<\/td>\n345g* (add an extra 120g for an adapter)<\/td>\n<\/tr>\n
MFD:<\/td>\n0.3 meters (max mag. 1:6.25)<\/td>\n<\/tr>\n
Aperture blades:<\/td>\n9<\/td>\n<\/tr>\n
Aperture range:<\/td>\n1.8 – 22<\/td>\n<\/tr>\n
Coatings:<\/td>\nGhostless, S.M.C.<\/td>\n<\/tr>\n
FOV:<\/td>\n69,8\u00b0 (diagonal)<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
Availability<\/span><\/address>\n
The Pentax 31 Ltd \u00a0sells for $600-900 at\u00a0<\/span><\/span>ebay.com<\/a>\u00a0o<\/span><\/span>r you can\u00a0<\/span>purchase<\/span>\u00a0the 31 Ltd at Amazon<\/a>, B&H<\/a> or Adorama (affiliate links). <\/a><\/span><\/span>Given the popularity and age of the lens, it’s easy to find copies new or used.<\/address>\n

Size, Adapters, and Build<\/h1>\n

The 31 Ltd is wonderfully built: all metal, mechanical, light, sturdy, tactile, and refined. I wish more manufactures took this approach.<\/p>\n

The 31 Ltd is a “screw driven” autofocus lens when mounted natively. Because of this, the lens has a shorter focus throw than most manual focus lenses. We have hard stops at MFD and infinity. The focus ring turns the same direction as Nikon lenses, and the opposite of Zeiss\/Canon\/Leica\/Fuji\/etc. This took me some time to get used to, and can still be annoying when shooting along side other lenses.<\/p>\n

The 31 Ltd is not environmentally sealed like newer lenses. Having said that, I shot the lens in humid, rainy and sandy environments without issue thus far. The aperture ring displays full stops starting at f2, but rests at unmarked half stops, except between f16 and f22. Each half stop has a light but definite click. The lens sports a permeant hood, which I dislike as it makes the lens heavier and longer than necessary. For the attached hood, I wish Pentax would have at least made it collapsible like on the 77 Limited.<\/p>\n

While the naked lens is not large or heavy at 345g, an adapter is required. My adapter weighs about 120g. The total weight of the lens+adapter is relatively light for a fast DSLR 35mm-ish setup at 470g. However, the adapter bumps up the compact size, turning this into a medium sized but well balanced partner on the A7iii. Here’s is the unadapted lens by the FE 28 f2.<\/p>\n

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And mounted on the a7iii:<\/p>\n

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Versions<\/h1>\n

I know of no documented changes over the production run. Some shooters do prefer copies made in Japan over those manufactured in Vietnam because of supposed quality control issues. Of the three copies I have owned, 2 were produced in Japan and 1 in Vietnam. Of the Japanese copies, one wasn’t as sharp as my other two copies. The perfectly centered copy used for the review is Vietnamese. I would not put much stock in the QC issues until I see some more serious documentation and\/or evidence.<\/p>\n

Handling<\/span><\/h1>\n

The manual focus rings runs 90 degrees from 0.3 meters to infinite. The resistance is light, which I find desirable for fast focusing. The focus rings is textured metal and has no play, making focus precise. The front element extends about an inch when at MFD. For those who use shimmering to manual focus, you’ll be pleased with the 31 ltd. Because of the smaller 90\u00b0 rotation, light resistance, lack of play, bright aperture and shimmering I often use the Pentax over my other lenses as I have a much higher rate of keepers (in focus photos). I love manually focusing on this lens, and it greatly contributes to my usage and output. However, I do wish the focus ring turned the opposite direction, like Zeisss\/Leica\/Canon not Nikon. Other than this, I wish I could focus my other MF lenses this quickly and accurately. \u00a0\"\"<\/p>\n

Optical performance<\/h1>\n

Sharpness<\/h2>\n

I wasn’t sure what to expect here, but the 31 Ltd does very well in resolving the entire 42 MP sensor at infinity relatively quickly. See crops below:<\/p>\n

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31 ltd full show crop selection<\/figcaption><\/figure>\n
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31 limited infinite crops<\/figcaption><\/figure>\n

f1.8:<\/span> Good sharpness in the center and midzone, but corners aren\u2019t sharp. Contrast is good, but with slight softness over fine detail due to spherical abrasions. Moderate but correctable axial fringing.<\/p>\n

f2.8<\/span>: Softness is gone, minimal color fringing. Sharpness extends to the outer midframe, corners bump to decent.<\/p>\n

f4<\/span>: Everything looks terrific, except for the very extreme corners, which are only good if pixel peeping. I wouldn’t hesitate to use it for landscape though.<\/p>\n

f5.6:<\/span>\u00a0 Perfect across the entire frame, except for the extreme corners which are only very good.<\/p>\n

f8<\/span>: Perfect across the entire frame.<\/p>\n

f11<\/span>: Very slight loss of sharpness as diffraction sets in.<\/p>\n

Summary<\/span>: The 31 ltd has terrific resolution into the absolute corners, even on a 42 mp full frame sensor. By f2.8 it is usable for landscapes if you don’t need high crispness in the extreme corners. F4 is sharp everywhere. From 5.6-f11 you have to zoom in to the utmost corner on a 42mp files to see any notable differences.<\/p>\n

Flare\/Ghosting<\/strong><\/h3>\n

I would rank the 31 ltd as only ok in real world shooting here. The ZM 35 1.4<\/a> and especially the CV 35 1.7<\/a> fare better with more modern coatings and smaller front elements. Shooting directly into light, there is very little loss of contrast.<\/p>\n

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Ghosting<\/h3>\n

This is one area the 31 Ltd does poorly. I often use it as a nature lens, but you have to be careful in strongly backlight situations with direct light. As stated above, there is little loss of contrast. However, ghosting artifacts do appear. They can be large and distracting. You can see the ghosting change shape as we stop down.\u00a0Here’s what I mean:<\/p>\n