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SMC Pentax-A 28mm f/2.8
© 2008 KenRockwell.com. All rights reserved.

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Pentax 28mm lens

Pentax 28mm f/2.8 SMC-A. enlarge. I'd get mine at these direct links to it at Adorama and eBay. It helps me keep adding this old stuff to this site when you get yours through these links, thanks! Ken.


December 2008      More Pentax Reviews


Ideal Uses: Perfect for use on Pentax as a compact wide-angle lens.

Not for: Autofocus. This is a manual focus lens. It works on AF cameras, but you must focus manually.

Ergonomics: (manual focus)


Introduction       top

Intro    Specs    Performance    Recommendations

This is a small wide-angle lens for Pentax' K-mount. It works on just about anything Pentax. I tried it on the Pentax ME.

It feels really nice to use. It feels solid, and it's all metal. The rubber focus ring and metal aperture ring have just the right knobby knurling to feel like a man's lens.

Heck, if I had tried these Pentax SMC Lenses back in the 1980s when I switched to Nikon, I just might have gone to Pentax. These are much nicer than Canon's FD lenses.

What's hard to describe is just how nice, tight, precise and solid these feel. The focus is more damped (stiffer) than Nikon, but still easy to turn with just one fingertip.

My biggest complaint are the goofy click stops on the aperture ring. One of the several reasons Nikon reined as the only 35mm camera system seriously considered by real pros in the 1970s and 1980s is that all Nikon's lenses have click stops at each full stop. It's easy to set apertures by feel with a Nikon lens. Want a stop more exposure? That's one click.

This Pentax lens has full stop clicks between f/2.8 and f/4, and between f/11, f/16 and f/22. It has half-stop clicks between (unmarked) f/4 and f/11. When shooting in the field, good luck trying to guess which is which by feel, especially since the diaphragm ring has different spacings between f/2.8 and f/4 and f/4 through f/22.

It's colorful, almost as pretty as Nikon's AI and AI-s lenses, with their color-coded depth of field scales. This SMC Pentax-A 28mm f/2.8 has a pale yellow index bump, bright orange scale index and IR index, deep orange for 10 feet, 3 meters and f/8, blue for feet, yellow for meters and white for what's left.

It works great. It's easy to focus, has great evenness of illumination even wide open and great center sharpness at any aperture. It's only weaknesses are softer corners and sides wide-open, but this rarely matters for anything other than deliberate tests, and is fine stopped down.

It looks good, too. It is solid, precise, well proportioned and beautiful.

Pentax 28/2.8

Pentax 28mm f/2.8. enlarge.


Specifications with commentary  back to top

Intro    Specs    Performance    Recommendations

Lens Mount: Pentax K.

Optics: 7 elements in 7 groups. Pentax Super Multi-Coated.

Diaphragm: 5 blades, stops down to f/22. Bizarre half and full stop clicks.

Filter Thread: 49mm.

Close Focus: 1 foot (0.3m).

Maximum Reproduction Ratio: 1:8.

Size: 2.5" diameter x 1.4" long (63 x 36.5mm), rated.

Weight: 5.920 oz. (167.8g), measured. 6.0 oz. (170g), rated.

Pentax 28mm, rear

Pentax 28mm f/2.8. enlarge.


Performance  back to top

Intro    Specs    Performance    Recommendations

Performance isn't up to either manual focus Nikon Nikkor 28mm f/2.8 AI or 28mm f/2.8 AI-s, but its way beyond the performance of third-party 28mm /2.8 lenses. It's a little better than today's Nikon AF 28mm f/2.8 D.



There's some coma at f/2.8 and f/4. Its gone by f/5.6.



The Pentax 28/2.8 has minor barrel (bulging) distortion.

This can be corrected for critical use by plugging these figures into Photoshop CS2's lens distortion filter. These aren't facts or specifications, they are the results of my research that requires hours of photography and calculations on the resulting data.

On Film
10' (3m)
5' (1.5m)

© 2008 KenRockwell.com. All rights reserved.


There was some, but not a lot, darkening of the corners at f/2.8. As usual, it got better at f/4 and went away entirely at f/5.6.



Focus is easy. I can do it with one firm finger.


Lateral Color Fringes




Used properly, it's sharp!

The sample I had was much softer on the right side wide-open, but fine on the left. This went away stopped down.

I sw these results both with an 8x Peak loupe and with 3600 DPI scans, both on Fuji Velvia 50.

f/2.8: Great center, but the corners are soft.

f/4: Better than f/2.8.

f/5.6: Sharp all over.

f/8: Optimum; very sharp all over.

(diffraction limits sharpness on all lenses at f/11 and smaller)


Recommendations   back to top

Intro    Specs    Performance    Recommendations

This is a swell, compact lens. I'd have no problem making fantastic images with it.

If you need the corners super-duper sharp, stop down a little.



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Thanks for reading!


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