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SMC Pentax 20mm F4 Review RSS Feed

SMC Pentax 20mm F4

Reviews Views Date of last review
8 91,452 Sun January 7, 2018
Recommended By Average Price Average User Rating
100% of reviewers $330.00 9.13
SMC Pentax 20mm F4

SMC Pentax 20mm F4
SMC Pentax 20mm F4

This slow extreme-wide-angle lens also exists as an M version, although different optically. It was later improved to f/2.8 in A and FA variations.

SMC Pentax 20mm F4
©, sharable with attribution
Image Format
Full-frame / 35mm film
Lens Mount
Pentax K
Aperture Ring
Yes (no A setting)
Automatic, 5 blades
12 elements, 10 groups
Mount Variant
Check camera compatibility
Max. Aperture
Min. Aperture
Min. Focus
25 cm
Max. Magnification
Filter Size
58 mm
Internal Focus
Field of View (Diag. / Horiz.)

APS-C: 72 ° / 62 °
Full frame: 94 ° / 84 °
Dedicated hard case
Lens Cap
Plastic clip-on
Weather Sealing
Other Features
Diam x Length
63 x 57 mm
300 g
Production Years
1975 to 1977
Engraved Name
Product Code
User reviews
Manual FocusAperture RingFull-Frame SupportDiscontinued
Price History:

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Sort Reviews by: Date | Author | Rating | Recommendation | Likes (Descending) Showing Reviews 1-8 of 8
Forum Member

Registered: April, 2014
Posts: 61

2 users found this helpful
Lens Review Date: January 7, 2018 I can recommend this lens: Yes | Price: $400.00 | Rating: 9 

Pros: image quality, sharpness, buid quality, focus throw
Cons: rare
Sharpness: 9    Aberrations: 9    Bokeh: 7    Handling: 10    Value: 8    Camera Used: sony a7r   

I already own the m 20 f4 which I have reviewed previously.
As a great fan of the k series lenses, I couldn't resist purchasing the K20 f4 when I eventually found one for sale.
Like all the other K series lenses that I own (28 F3.5, 35 F3.5, 55 f1.8 and 85 f 1.8), it has excellent build quality and has a long focus throw which makes focusing with the image magnifier and focus peaking easy to achieve and consistently.
The lens produces deep and vibrant blues and greens with lovely clarity and contrast.
It is sharper than the m version but only if one pixel peeks.
It has less distortion than the m version which is only relevant for architectural photography.
The image quality is not significantly surpassed by the modern and vastly more expensive zeiss loxia 21 that I own.

In conclusion: If you are looking for a good quality ultra wide angle lens for landscape and even architectural photography then I would highly recommend this lens to you.
Junior Member

Registered: March, 2014
Posts: 27

2 users found this helpful
Lens Review Date: August 3, 2016 I can recommend this lens: Yes | Price: N/A | Rating: 9 

Pros: Build quality, sharpness, not much vignetting
Cons: size, weight
Sharpness: 10    Aberrations: 10    Bokeh: 9    Handling: 10    Value: 9   

Already owned the M20/4 and loved the small size of that lens, but since I collect K lenses I got this lens when I found it as part of a complete set. Sold everything except the K20/4 and compared it with the M20/4 on both M43 and 35mm.

The K20/4 is quite a lot sharper than the M20/4. Not only in the centre but even more noticeably towards the corners. Don`t like pixel peeping too much but it was pretty obvious, the K version actually impressed me on sharpness as much as the M version impressed me on size

That is why I sold the M20/4, which is still a fine lens as well and it is almost half the size...

Where the K20/4 disappoints a little is the distortion on fullframe, it has a moustache distortion that I didn`t expect after reading the reviews. It`s not too bad, only when you place straight horizontal lines closer to the top or bottom of the frame it becomes visible, but my Zuiko 21mm f3.5 does better and is as small as the M20/4. For landscapes it does a very fine job though, see the photos which are not corrected at all.

For the use on the LX I like the K20/4 a lot and after this summer will try it out on a K30 aps-c. I think the distortion will be hardly visible and I`m sure it will be a great manual wide for that body.

LX & K20/4 @ 5.6

LX & K20/4 @ 11
New Member

Registered: July, 2012
Posts: 4
Lens Review Date: July 3, 2016 I can recommend this lens: Yes | Price: N/A | Rating: 9 

Pros: Sharp, easy handling.
Cons: Expensive
Sharpness: 10    Aberrations: 10    Bokeh: 9    Handling: 10    Value: 9    Camera Used: Sony A7II   

I really love this lens and Pentax-K lenses in general. Distortion is ok. Use of the hood is needed.

Site Supporter

Registered: January, 2010
Location: The Black Hills
Posts: 1,099

1 user found this helpful
Lens Review Date: August 20, 2013 I can recommend this lens: Yes | Price: $325.00 | Rating: 10 

Pros: Very sharp, contrasty, lack of distorsion.
Cons: Could be faster, but I am happy, needs a hood.
Sharpness: 10    Aberrations: 10    Bokeh: 8    Handling: 9    Value: 10   

This lens has totally lived up to my expectations. There are not a lot of reviews or that much info out there, but I had a feeling this might be a standout, and for me it is. I love it on my K-5 and would love to try it out on a FF Pentax some day. Its colors are a little cooler than my DA 15ltd, but that is easily fixed (if you want to).
Some samples with some PP and no cropping.

Veteran Member

Registered: June, 2010
Posts: 753

1 user found this helpful
Lens Review Date: June 20, 2011 I can recommend this lens: Yes | Price: $255.00 | Rating: 9 

Pros: sharp, nice colour rendition, low distortion, absent CA, great build, nicely balanced on K20d
Cons: rare, hood is difficult to find, f4 not useful for interior shots, overexposes on dSLR, flare
Sharpness: 9    Aberrations: 10    Bokeh: 6    Handling: 10    Value: 9    Camera Used: K5, K10D, K20D   

I give this lens 9 but it is not flawless, please note that I'm using it almost exclusively outdoors. This lens is quite new in my collection so I'll update my review after more time with it.

So far i can only tell you this: K20/4 is by far the best UWA lens i've tried. I had Tamron SP17, DA 16-45, K18/3.5 and Olympus 21/3.5 and only highly regarded Olympus is fairly comparable, but not as good as Pentax.
Centre sharpness of this lens is very good wide open, excellent at 5.6 and 8. Edge sharpness stopped down seems to be quite good, although FA20-35/4 seems to have better corner sharpness. Lens is nicely corrected for distortion so shooting architecture is not problem. So far I haven't been able to spot any traces of CA or purple fringing! The lens build is very good as is typical for K-series - it just ads some joy to taking photos - feeling of quality when handling those wonderful original series Pentax lenses. It is very well balanced on dslr bofy, in fact one of three best balnced lenses i have alongside with FA31 and K85. It is nearly the same size as FA31 limited and K105 so neither big nor small - ideal for me. In fact it makes nice pair with 31 as they can share same filters. Only optical con I find that it produces flare when shooting in the sun more often then other Pentax lenses I have/had.

I purchased it mainly for landscapes, but on dSLR i quickly found out hat it is also nice lens for street photography, when you like to play with perspective a bit. It's only 2mm 'thinner' than K18, but I find photos from K20 much more natural. Given the price I paid for it it seems to me that so far it was a greatest deal I made with Pentax lens.
Forum Member

Registered: March, 2010
Posts: 72

3 users found this helpful
Lens Review Date: July 9, 2010 I can recommend this lens: Yes | Price: $400.00 | Rating: 9 

Pros: Excellent IQ
Cons: Heavy, overexposure

The K20/4.0 is an ultra-wide prime from the analog era that functions as a wide prime on cropped sensors. I have compared the K20/4.0 on digital with the DA21 and the Tamron 17-50. My conclusion is that K20 outperforms the other two, in terms of detail rendered and in terms of liveliness of colors. It is not as superbly sharp as K28/3.5 or K35/3.5, but it's better than the widely acclaimed DA21 or a very good zoom like the Tamron.

Given that I paid roughly the same amount for K20/4.0 as for a 2nd hand DA21, and given that IQ speaks in favour of K20, would there be arguments against K20 ?
- The K20/4.0 is manual focus, obviously, but that does not speak against it: this is a lens that you would use primarily for landscape and architecture, i.e. with infinity focus.
- The K20/4.0 is sensitive to flare, and tends to overexpose a bit. With a lens like this, you're an active shooter anyway, so that's something that can be controlled. (When metering with the green button, I get good results when I meter on the brightest spot in the scene.)
- The K20/4.0 is a lot bulkier and heavier than DA21. This is probably the main feature that would speak in favour of DA21. If you are ready to carry along your gear with the main purpose of shooting pictures with high IQ, go for K20/4.0. But for casual shooting, you may be better served with the unobtrusive DA21 or a good zoom like Tamron 17-50.

Addendum July 2011.
I have now been able to compare K20/4.0 to the Zeiss Distagon 21/2.8 - a lens with well known cult status and reference point value. The trivial part of the conclusion is that K20/4.0 no longer feels heavy More importantly, as far as image quality is concerned, K20/4.0 performs on the same level as the Distagon as far as center resolution is concerned; in the corners, the Distagon wins. Also, there is more purple fringing and somewhat more distortion in the K20/4.0. Overall, my appreciation for K20/4.0 has risen in the comparison: the Distagon is the better lens, but the Pentax lens is definitely a very good one.

PS The price mentioned is a euro to dollar conversion as of mid 2010.
Inactive Account

Registered: February, 2009
Posts: 7
Lens Review Date: September 7, 2009 I can recommend this lens: Yes | Price: $250.00 | Rating: 10 

Pros: FANTASTIC color and contrast "3D" rendition, sharpness, low distorsions
Cons: quite big for a f/4 lens, ghosting and flare when shooting in front of the sun (without hood)

Like all others K lenses it is just so fantastic to use with their smooth focusing ring. This wide angle has deap big glasses, a pleasure for the eyes, and what is really astonishing is the rendition with contrasty and saturate pictures, like the Limited lenses can offer.
Examples :
Site Supporter

Registered: October, 2008
Location: Vancouver, Canada
Posts: 7,586

7 users found this helpful
Lens Review Date: July 18, 2009 I can recommend this lens: Yes | Price: $350.00 | Rating: 8 

Pros: Angle of view of 94 degrees on a film camera, build.
Cons: Maximum aperture of f4.0, no built-in filters.
Camera Used: Pentax film bodies (K1000, KM, KX, K2, K2DMD, MX, LX, Super A, P50)   

The K20/4 is the middle of three Pentax K series ultra wide angle lenses, with a 58mm filter diameter. The three lenses are the K18/3.5, the K20/4 & the K24/3.5 and they also share a common lens hood pictured below. All three lenses are somewhat hard to find, as they only had a three year production run (1975-1977). The K18/3.5 being the exception, it had a ten year run. (1975-1985)

The K20/4 is about twice the weight of its replacement the M20/4, so there is no mistake it’s a K series lens. If you happen to like your lenses with some “meat” on them, then the K20/4 will not disappoint. Along with the 58mm filter thread, it looks perfect mounted on my black K2.

The maximum aperture of f4.0 is adequate for most daytime shooting, but the K24/2.8 is a better K series WA lens for indoor or low light situations. The K20/4 has an angle of view of 94 degrees on a film camera, so it can capture large landscapes very well.

With a WA lens of this focal point, vignetting is an issue. I have a Pentax Polarizing Filter guide and it indicates the use of a polarizer on the K20/4 will cause vignetting. I did my own test with a regular sized UV filter & the K20/4 dedicated lens hood and found no vignetting issues.

The K20/4 is very close to the K18/3.5 in focal length, sharpness and size, but it will cost you about half in price. However for a film user like myself the K18/3.5 is preferred, as it has various built in filters and is slightly faster. For a digital user the K20/4 may be a better choice.

Here is a picture of the three K series ultra wide angle lenses:

Sample shots taken with the K20/4. Photos are medium resolution Lab scans from original negatives or slides.

Camera: LX Film: CineStill Film ISO: 50

Camera: K2 Film: Fomapan R100 Processed in DR5 Chrome ISO: 160

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