Pentax FA 35mm f/2 AL And FA Zoom 20-35mm f/4 AL

Peter K. Burian  |  Nov 1, 2000

Autofocus performance with the FA 35mm f/2 AL lens on a ZX-7 was excellent, even when I used a polarizer that reduced the amount of light transmitted to the AF sensors. This is a secondary advantage with such wide aperture lenses. (At 30mm; f/5.6; flash; Sensia II 100.)
Photos © Peter K. Burian, 2000

After several years of focusing on the compact camera market, Pentax has been working aggressively to expand its 35mm and medium format SLR systems.

Two mid-priced wide angle lenses with aspherical optics to assure high imaging performance are an addition to their strategy. Light and compact the FA 20-35mm f/4 AL and the tiny FA 35mm f/4 AL are certainly not lightweights in terms of optical quality. In comparison to the massive FA* 28-70mm f/2.8 AL, it was a pleasure to carry this duo on family outings, while running around documenting several parades, and when hiking for autumn landscape photography.

Common Characteristics. Al-though one is a zoom and the other features a fixed focal length, these lenses share a strong family resemblance and design qualities as follows:

Not everyone can afford the f/2.8 ultra-wide zoom. Fortunately, much wide angle photography is done at small apertures, so the more affordable FA 20-35mm f/4 AL lens is a suitable alternative for many photo enthusiasts. (At 24mm; f/8; Tiffen polarizer; fill flash; Sensia II 100.)
  • Extensive use of impact resistant polycarbonate for light weight. Used by most every manufacturer now, this material is highly suitable for lenses which will not receive professional abuse. (The mounts are made of stainless steel, however.) Nicely finished in satin black, both include an aperture ring with detents at half stops at the wider apertures up to f/11. The distance scale under glass is highly legible with black numerals on a sliver base; the zoom features an IR index to guide focusing with infrared film.
  • Maximum apertures are relatively wide, especially for the zoom. Most 20-35mm zooms feature variable apertures such as f/3.5-4.5, while this Pentax model maintains f/4 at all focal lengths, appreciated especially when using an accessory light meter.
  • Manual focusing is precise, thanks to a fairly well damped mechanism. The (rubberized) focusing rings do rotate in AF operation but they are narrow and located at the very front of the barrel, so my hand did not impede their movement. The rotary zoom mechanism of the 20-35mm lens is smooth as well but this lens has no depth of field scale: a common omission these days. The 35mm lens has a scale for f/8 to f/22.
  • The AF sound level (high pitched, especially noticeable with the 35mm lens) is comparable to that of many lenses and autofocus speed is very good. The internal barrel of both lenses protrudes a bit in close focusing, but does not rotate; this makes using a polarizer or graduated ND filter a pleasure as the effect does not shift while focusing.
  • Anti-flare strategies include SMCP multi-coating and a removable notched (corner-cut) hood designed to shade the front element--at all focal lengths with the zoom. On the test samples, these were very loose when mounted; it was easy to inadvertently change their position so they intruded into the image area. I solved this with a short strip of "invisible" cello tape. These hoods have a removable section that allows you to easily adjust a polarizer without removing the hood or taking the camera from eye level to fiddle with the filter. The Pentax designers should be congratulated for this innovative concept.
    • Although extreme sharpness is often desirable in a photograph, wide angle lenses such as the FA 35mm f/2 AL can also be useful for more creative effects. Here, I set a 1/15 sec shutter speed and panned with the subject, producing some blur for a sense of motion in a still photograph. (Fill flash; Ektachrome E100VS.)

    Aspherical Optics. Both lenses include one or more "aspherical" elements. These correct spherical aberration (curvature of field) for more consistent edge to edge sharpness at wide apertures, counter comatic flare, and reduce linear distortion. Today, several manufacturers use new methods for creating affordable aspherical elements: such as bonding resin to the glass to form a non-spherical surface layer. The "replica" or "hybrid" (as Pentax calls them) aspherics allow compact AL lenses to compete with the expensive "Pro" AL lenses (with their ground and polished aspherical elements).

    As Bob Shell has written, such elements produce "anomalous refraction, bending the light to different degrees depending on where the light passes through the lens. This is achieved by varying the curvature which changes across the lens surface from the optical axis out to the edge." With such elements, the designers can reduce the number of lenses required for high edge to edge sharpness even at wide apertures. Thus, overall weight and the propensity for flare (typically worse with more air to glass surfaces) can also be minimized.

    Thanks to the unique lens hood of both AL lenses, adjusting a polarizer--without removing the hood--was extremely convenient. At the most commonly used f/stops, the zoom provided excellent image quality and freedom from flare. (At 24mm; f/16; Tiffen polarizer; Ektachrome E100VS.)

    Performance Evaluation. I always carry an ultra-wide zoom, frequently employing the "exaggerated" spatial perspective--an optical illusion causing foreground objects to become more prominent. As well, 20mm is more useful in cramped quarters or when you cannot back up any further to include an entire panoramic scene or a large group of people. None the less, a fast 35mm f/2 lens remains popular, particularly among photographers who will not consider zooms for serious photography. I made the following notes while examining my slides under a 10x loupe:

  • In images of a brick wall made with the zoom, I noted some barrel distortion (bowing outward of straight lines near the edge of the frame) at the short focal lengths. In formal architectural photography, this would certainly create a concern, but that's not the intended use for lenses of this type. With the 35mm AL lens, linear distortion was minimal, barely noticeable.
  • Flare is very well controlled with the zoom, occasionally noticeable at f/4 to f/5.6. At the more commonly used small apertures, neither flare nor ghosting created a problem, except in strong backlighting. The 35mm AL lens is almost impervious to flare except in extreme conditions.
  • From f/5.6 to f/16--the most commonly used apertures with wide angles--the zoom produced highly satisfying slides at every focal length, suitable for a fine 11x14 print or a double page magazine spread. Peak optical performance--adequate for a fine 11x14 print--was obtained at the 28-35mm focal length range, at f/8 to f/11.
  • The 35mm AL lens offered even higher sharpness especially at f/4 and at f/22 with optimum results--excellent--at f/11. Use a high-resolution film and a tripod and your negatives should produce a fine 16x20 print in the mid range of apertures.
  • With the zoom, light falloff at the edges is moderate--noticeable when a white wall or clear sky fills the frame--at f/4 and disappears by f/8. There is less darkening of the corners with the 35mm lens and none by f/4.
    In addition to the above, the fixed focal length lens has two advantages over the zoom. Its maximum aperture is two stops wider, allowing the use of slower (high-resolution) film in handheld photography, and reducing the need for flash or a tripod in low-light situations. It is better corrected for linear distortion, but this factor may not be relevant to many photo hobbyists. However, the FA 35mm f/2 AL does produce images with higher sharpness at the edges of the frame in the f/4 to f/5.6 range; even at f/2 or f/2.8, the optical performance is impressive: suitable for an excellent 8x12 print.

    • Conclusion. The outcome of my tests speaks very highly of the computerized design capabilities of the engineers at the Asahi Optical Co. Ltd., the Pentax parent company. With both AL lenses, I was especially pleased with the consistency of sharpness across the entire image in the mid range of apertures. This is particularly important with a wide angle lens where some subject matter is often included near the extreme edges of the frame.

    Most photo enthusiasts--particularly those who don't want to lug extra pounds of equipment--will be well served with either of the two lenses tested. Yes, the FA 35mm f/2 provides the highest image quality, but the zoom is a fine performer, too, and is more versatile. Given my own shooting style and choice of subjects, I would want the latter. For my stock photography business, magazine covers, full page newspaper spreads, and wall decor, I would be happy to own either model. Whether for land or cityscapes, informal architectural work, travel photography, or environmental portraits, these AL lenses should satisfy most serious photographers.

    Pentax FA 43mm f/1.9 Limited Editions

    Pentax FA 43mm f/1.9 Limited Edition
    Pentax also provided a sample of their 43mm lens with satin titanium finish, a perfect match to any of the ZX-series cameras with similar coloring. Although it is an autofocus model, this 5.5 oz "ultra-thin" lens is reminiscent of those made three decades ago. Naturally, it incorporates computer-designed optics (seven elements in six groups) and the latest SMCP multi-coatings in order to compete with the finest current lenses.

    This lens is a limited production model, but Pentax will manufacture enough of them to meet demand. And you'll want one too after trying it for even a single roll. Aside from the impeccable construction and mechanical operation, it offers optical performance as befits the price: absolutely superb at all apertures from f/4 to f/16. The wider apertures are primarily useful for problem-solving in low-light situations where flash and tripod are impractical. In extreme close focusing (to 17.8") excellent results are provided at all f/stops, particularly impressive in the f/5.6 to f/11 range. Stop down when possible and you can expect image quality suitable for beautiful 16x24 prints when using professional photographic techniques.

    Like all Pentax FA lenses, this one can be used on manual focus cameras as well, even those with screwmount, with an adapter. Yes, it is expensive as one would guess from the metal construction, milled focus and f/stop rings, finely engraved numerals, and the metal (well flocked, screw-in type) hood and lens cap that fits over the hood. The 43mm semi-wide focal length is not common today, but this is no common lens. Intended for the discriminating photographer, the FA 43mm f/1.9 offers high prestige value, excellent build quality, and an elegant retro-look that harks back to the earlier days of photography.

    Pentax SMCP-FA 35mm f/2 AL.

    Technical Specifications

    Lens: FA 35mm f/2 AL
    Mount:     KAF; also fits manual focus K mount and screwmount with adapter
    Angle Of View (diagonal): 63
    Minimum Aperture: f/22
    Optical System: 6 elements in 5 groups; one aspherical; SMCP multi-coating
    Min. Focus Distance: 12" (30cm)
    Maximum Magnification: 0.17x
    Filter Diameter: 49mm
    Accessories: Removable hood provided
    Dimensions/Weight: 2.5x1.8"; 6.9 oz (64x44.5mm; 195 g)
    Pentax SMCP-FA Zoom 20-35mm f/4 AL.

    Lens: Pentax FA 20-35mm f/4 AL
    Mount:     KAF; also fits manual focus K mount and screwmount with adapter
    Angle Of View (diagonal): 94 to 63
    Minimum Aperture: f/22
    Optical System: 10 elements in 8 groups; two aspherical; SMCP multi-coating
    Min. Focus Distance: 12" (30cm)
    Maximum Magnification: 0.16x
    Filter Diameter: 58mm
    Accessories: Removable hood provided
    Dimensions/Weight: 2.7x2.7"; 8.6 oz (69.5x68mm; 245 g)

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