| Author: | | Pentaxian Registered: October, 2009 Location: North Posts: 4,709
9 users found this helpful
| | Review Date: February 2, 2015 | Recommended
| Rating: 9 |
| Pros: | small; good flare performance; generally good at f11 on FF | | Cons: | corners can be a bit sharper stopped down on FF | | Sharpness: 8
Aberrations: 8
Bokeh: 7
Handling: 9
Value: 9
Camera Used: K30; Sony A7
| |
This lens made little sense on APS-C so it never passed my mind to get one.
But with use of Pentax lenses on FF, I re-explored what was available and got hold of one.
DSC08446-2400 by jenkwang, on Flickr
This is a real small lens for a 20mm.
Roughly speaking about 2/3 the length of a Canon EF50/1.8 for those more familiar with that lens.
Or the same size as a M28/2.8.
Few makers seem to want to make smaller more portable f4 wide angle primes anymore, which is a pity imo as very often such FL see more use as a f8 and smaller wide view / landscape lens than anything else, so less need for a f2.8 which adds to the weight and size.
DSC08453-2400-bw by jenkwang, on Flickr
DSC08510-2400 by jenkwang, on Flickr
20150131-DSC08642-2400 by jenkwang, on Flickr
It seems that the lens is nicely resistant to flare (as in sample shots)
Field curvature seems real slight (almost none) compared to other legacy faster 20mm which tends to have a significant amount that needs to be taken care of during focus.
f8 is generally good, with some softness only in the corners (tips), perhaps a hint less sharp on the last 1/10 of the frame.
Thats not uncommon for many legacy 20mm (and even quite a few more modern wides).
The latter may also be an artifact of the thick sensor stack of the A7 series cameras.
f11 is probably where I want to set if I want better corners and no issues at all on the edges.
Sharpness up to the edge at f11 is no complaints at all.
Its the far corners that will be soft(er).
I would have given a higher sharpness score if not for the corners (and corners only)
Overall, a great portable option.
Far under rated imo having tried the FA20 and the Canon FD20, especially when one considers encumbrance and actually carrying the lens for days on a trip matters and cost.
| | | | | | | Pentaxian Registered: February, 2010 Location: Northern Michigan Posts: 6,174
9 users found this helpful
| | Review Date: May 26, 2011 | Recommended | Price: $285.00
| Rating: 9 |
| Pros: | Compact, good contrast, excellent color rendition | | Cons: | Some distortion, soft wide open | | Sharpness: 8
Aberrations: 8
Bokeh: 7
Handling: 10
Value: 9
Camera Used: K-5, K-1
| |
This is a lens I bought years ago for use with the Pentax K-5. At the time, I found myself preferring images from this lens to what I was getting from the DA 12-24. So I sold the zoom and bought the DA 15 as a companion piece for the M 20. Over the next few years the lens produced some very nice images. But eventually, I wound up acquiring the DA 21, and after that the M 20 received virtually no use at all. For while there's not much difference in terms of sharpness between these two wide angle lenses (at least not on APS-C cameras), the DA 21 tends to produce contrastier and more beautifully saturated images.
Here are some images of M 20 on the K-5:
More recently I have had the opportunity to shoot the M 20 on a K-1. I haven't been quite as impressed with the M 20 on FF as I was with the lens on APS-C. Some of the flaws of the lens, such as the infamous "mustache" distortion, light fall-off toward the corners, and softness in the corners (even when the lens is stopped down), become more of an issue on FF. On the plus side is the small compact size of the lens. Compared, say, to the DFA 15-30, which seems about ten times as large and heavy, the M 20 is a dream to handle and use. And stopped down to f11 or f16, there's hardly any difference in terms of sharpness between the two lenses, except for those pesky corners. But the huge zoom wins handily when it comes to contrast and color saturation. The images just look better. Nevertheless, I'm glad to have the M 20. It makes for a great compact, light-weight alternative when I need to use filters on a wide angle lens.
Here's a few images shot with the M 20 and the K-1:
 | | | | | New Member Registered: April, 2021 Posts: 16
7 users found this helpful
| | Review Date: April 15, 2021 | Recommended | Price: $250.00
| Rating: 9 |
| Pros: | sharp (up to 10% of the border on FF). Excellent for APS-C where is scores 9 | | Cons: | Soft borders 10% and corners on FF | | Sharpness: 9
Aberrations: 8
Bokeh: 8
Handling: 8
Value: 9
Camera Used: K1 and K3
| |
I have just acquired the FA 20mm f2.8 for my K1. I already owned the M 20mm f4.
I am reviewing (both these) because I was unable to find an adequate comparison anywhere of the FA 20 f2.8 and the M 20 f4. Hopefully this review will help other folk choose between these two lenses.
My results are based on taking the same landscape with buildings detail and winter trees in the distance in the corners on a full frame K1, using both the FA 20 f2.8 and the M 20 f4, from f2.8 to f11 focused at infinity. I checked that both lenses focus correctly at infinity at all apertures before commencing; there is no obvious focus shift, which is good. Observations were made in Photoshop at 100%. (I am not posting images, because unless they are full size, which is impractical, there isn't any point.)
First the M 20 f4:
f4 soft all over. Significant light fall-off in corners.
f5.6 sharp in the centre but soft borders. Light fall-off improving.
f8 very sharp, until 10% of the borders. Within this boundary, the f4 is similarly sharp as the f2.8. To give an objective measure: A car number plate at 55 metres (on a 20mm lens the plate’s length is a mere 0.6% of the width of the frame which really is small) is just readable. Light fall-off towards the corners on the f4 is more pronounced at all apertures than the f2.8 but only slight at f8 and easily edited.
If I crop the 10% soft border on the 4, this increases the effective focal length from 20 to 24mm and the K1 file size reduces from 36 to 25mp. This is OK and excellent on my K3, but I wanted 20mm and the full K1 file size.
The FA 20 f2.8 on the K1 does not disappoint:
f2.8 Sharp border to border; softness in corners. Noticeable light fall-off towards corners but less than the M 20 f4
f3.5 Sharp border to border; mild softness in corners.
f4.5 Sharp border to border; very mild softness in only in very tips of corners
f5.6 - 8 Sharp corner to corner.
f11 just begins to soften from diffraction.
Light fall-off diminishes progressively when stopped down and is negligible at f8. CA and aberration are good.
Happily my f2.8 came with a hood. Being 20mm this doesn't look like it does much but as well helping with glare I think it actually helps generally to keep contrast up. As I will only use this stopped down for landscape, I can't comment on bokeh or distortion, but there is nothing obvious on the buildings in my images.
Finally, I should mention that my copy had a slight decentering problem and diagonal corners were not sharp when I acquired it (used); simply disassembling the rear group and re-assembling miraculously completely resolved this - either rotation of the group or simply reseating it must have achieved this.
In conclusion, excepting the border softness of the F4 on full frame (but does not affect APS-C users), these two lenses perform similarly and very well. The obvious advantage of the FA over M is it is fully automatic (and it seems to autofocus well). I don't mind manual for landscape but auto is obviously more versatile. It is still compact and light.
Sweeping statements that the f4 is completely inferior to the f2.8 need to be contextualised: the f4 is not up to full frame (K1) but is outstanding on APS-C (e.g. K3) where it is capable of a very sharp A2 print corner to corner; the f2.8 on a K1 is capable of a sharp corner to corner A1. Price and what you want it for will probably determine your choice.
| | | | | Veteran Member Registered: December, 2007 Location: Vancouver, British Columbia Posts: 336
5 users found this helpful
| | Review Date: December 20, 2010 | Recommended
| Rating: 9 |
| Pros: | lovely IQ, good build, compact | | Cons: | currently expensive, not all that wide on digital | |
I got this lens very inexpensively - very lucky yard sale find (along with a bunch of other Pentax gear). So I won't say exactly how much it cost 
Anyway, I only ever had a chance to run it through its paces with one roll of film (long expired generic KodakMax 400) and also took a few digital test shots.
I must say, on my Pentax ME, it had a certain indefinable quality and produced fantastic shots. I would call it ‘cinematic’ – kind of bold yet mysterious. I never experienced any perspective distortion, which is great considering just how wide this little prime is. The colors and contrast were always punchy and nice, and the sharpness was also excellent to my eye. It was a joy to compose with and to manually focus on the Pentax ME. Together, they made for such a nice little compact package. And the couple of images I got with this lens on digital (my Pentax K-x) also looked nice.
Unfortunately, I was silly enough to sell it, right here on the forum marketplace. Part of me wishes I hadn't. I hope the new owner holds on to it for quite a bit longer.
The reason I sold was I thought that a Sigma 10-20 would be a better and more practical choice for DSLRs. I believed f4 to be a bit too slow and the lack of AF and zoom to be downsides. In reality, for my style of shooting, the lightweight nature or this lens and its image quality outweigh those considerations by far. Oh well, live and learn I guess. Definitely, I'd say the images I got from the Sigma were much more prosaic and less 'cinematic', much less “wow” factor.
Here are a few sample shots from that one roll of cheap expired film on my Pentax ME:
 | | | | | | | Forum Member Registered: July, 2010 Location: Cardiff, UK Posts: 65
3 users found this helpful
| | Review Date: November 20, 2018 | Recommended
| Rating: 9 |
| Pros: | Compact, sharper than one has any right to expect | | Cons: | Nothing serious | | Sharpness: 8
Aberrations: 8
Bokeh: 6
Handling: 9
Value: 9
Camera Used: K3/Sony A7iii
| |
I have a couple of copies of this lens. One is significantly better than the other. On a Pentax K3 the lens is not really wide enough to stand out: it works well enough, but a 30mm equivalent f4 is nothing to shout about. On a 24x36mm sensor things are different. Once you stop down to f6.3 or f8 the lens is commendably sharp across the frame (very sharp in the centre) when used on a Sony A7. By f11 it is very good indeed. In fact, given how compact this lens is, the image quality is rather amazing. One can compare this usefully to the faster A series equivalent. The Pentax A 20mm f2.8 might be slightly sharper in the corners at f5.6 (neither is brilliant at this aperture, although the centre is fine on both). However, the f2.8 suffers badly from flare. The M f4 does not and is easy to carry in a pocket. A fine lens.
| | | | | Veteran Member Registered: May, 2009 Location: India Posts: 384
3 users found this helpful
| | Review Date: January 24, 2018 | Recommended | Price: $130.00
| Rating: 9 |
| Pros: | size, built, sharpness | | Cons: | Nothing, at least for the price | | Sharpness: 9
Aberrations: 8
Handling: 10
Value: 10
Camera Used: K1, K5iis, K-01
| |
When I first used the lens borrowed from a friend, I had a very bad feel about it's image quality. But, I have plans to upgrade to K1 and in need of a small wide-angle prime. When he is selling it for a good price, couldn't say NO and grabbed it. Got an opportunity to loan K1 and used the lens and was simply blown away by the performance of the combo this time. Such an old lens performing superbly on 36mp digital body is great. As many said, it is a well built, compact and typical pentax film era prime lens. What else.. check the pics attached.. weather is pretty hazy when I shot these pics, but I love them
 IMGP2155 by Tirumala Nalla, on Flickr
 IMGP2247-HDR by Tirumala Nalla, on Flickr
 IMGP2342 by Tirumala Nalla, on Flickr
| | | | | Forum Member Registered: April, 2014 Posts: 61
3 users found this helpful
| | Review Date: May 1, 2014 | Recommended | Price: $300.00
| Rating: 10 |
| Pros: | size, sharpness, colurs, contrast, build | | Cons: | none | | Sharpness: 9
Aberrations: 8
Bokeh: 9
Handling: 9
Value: 9
Camera Used: sony a7r
| |
   This is a great lens. Why??
It fits in one's pocket so it's not going to be left at home!!
The colours are so vibrant. The sharpness is great at f8.
Manual focus and the depth of field scale are excellent for control of depth of field and the hyperfocal distance.
Build quality is excellent. The focus ring is great and the aperture ring clicks true every time.
Distortion in landscape isn't noticeable.
Distortion in architecture is easily corrected in LR5.
This is a must lens for landscape photography.
| | | | | New Member Registered: October, 2007 Location: Toronto Posts: 4
3 users found this helpful
| | Review Date: May 28, 2010 | Recommended | Price: $200.00
| Rating: 8 |
| Pros: | Very Sharp, Short Minimum Focus Distance, Nice Colour | | Cons: | Slow at f4 | |
This was my second copy of this lens. For whatever reason, I sold the first one, and then bought another, but I was very upset when I bought this lens, because the aperture lever broke. Someone took it out so that it could be used on the Canon bodies, and it was GLUED back when it was sold to me. In any case, I have neglected this lens for more than a year until I started using it on the Digital Rebel 550D (this lens does not work on full frame Canon cameras).
I wish I had used this lens sooner. Such a small and lightweight lens is perfect match for the also petite Digital Rebel. I love the fact that anything after 2 meters is consider infinity, so that's where the focus usually stays. When used on non-full frame cameras, corner sharpness issues can be neglected.
The 20mm f4 is very sharp and contrasty. It's now my favourite lens!
Pentax K10D & 20mm f4 at f4:
Canon 20D IR Converted & 20mm f4:
Canon Digital Rebel 550D & 20mm f4:
 | | | | | Veteran Member Registered: December, 2007 Posts: 8,237
3 users found this helpful
| | Review Date: October 17, 2008 | Recommended
| Rating: 9 |
| Pros: | Very sharp, incredible color and contrast | | Cons: | none | |
This lens floors me - very sharp, and the colors are so rich and deep. I get a big smile on my face every time I go out with it - I have the 16-50 and the 12-24, and this is sharper than both at 20mm. A joy to use.
New photo, after finding my 'stolen' M20!
 | | | | | New Member Registered: February, 2016 Location: lake constance Posts: 1
2 users found this helpful
| | Review Date: March 10, 2016 | Recommended | Price: $300.00
| Rating: 10 |
| Pros: | plenty of sharpness, very compact and light, build, coating | | Cons: | edges could be darkened when using filters | | Sharpness: 10
Aberrations: 10
Bokeh: 9
Handling: 10
Value: 10
Camera Used: Sony A7
| |
For me, the Pentax M 4/20mm is a well built and compact companion for my MX and also Sony A7. To a compact camera belongs a compact and powerful lens. Robust in mechanics and excellent in optics too. That are the ingredients for a lifelong partnership. I bouht this one by a bargain and paid round about 160$ for it. It has some scratches on its body, but this doesn`t disturb me.
Very flexible use in creative landscape photography, because you fit this lens with small and affordable filters. I often use a big stopper with ND3.0 a modified polarizer ( otherwise vignetation possible ).
Additional i use a cokin gradual filter system. An enormous advantage of the M lenses is the fantastic smc coating - perfect in digital Full Frame too.
There are no ghosts by using filters. The M 4/20mm has a short way of focusing, is very light - perfect to handle on trips in landscape and nature. And here it lets combine with my Pentax M 3,5/24-35mm and M 1,4/50mm or M 1,7/50mm. But there is one thing to consider: you better make some aperture stops down to 8-11. In wide angle photography mostly needed. You have got a large depth of field. Then the corner have plenty of sharpness. And even the distorsion is not striking.
May be, the newer A lens 2,8/20mm has a better optical performance, but it is not so compact and is much more expensive. I often put this lens in my pocket of my coat or jacket.
It is impressive to me, how Pentax engeneers put such a know how into a lens in the 1970s. You don`t find any comparable 20mm lens in todays production worldwide. Pentax was unique in manufacturing well built compact lenses in the 1970s and early 1980s. Until today i think, no other brand reached this level of overall performance.
I believe, most of the Pentax users can support me in this opinion. Full Frame recommended in the past with for example the MX, today f.e. with Sony A7.
A morning at lake constance - Insel Reichenau
| | | | | Veteran Member Registered: February, 2009 Location: Perth, Western Australia Posts: 2,576
2 users found this helpful
| | Review Date: December 16, 2010 | Recommended
| Rating: 9 |
| Pros: | size, handling, optical performance | | Cons: | wide open performance | |
I purchased this lens intending to use it for both digital and film cameras, however I was not too sure how it would compare to my existing Pentax-M 28mm f/3.5, which is already very good in terms of sharpness, both on film and digital.
However as soon as I mounted the M20 to a film body, I was in love with the size and handling of the lens. It really is tiny - comparable to some of the small modern limited lenses.
On film the field of view is fantastic. Extremely wide, but I was surprised by how practical it is in use. I had some reservations that this lens would be special purpose only, but really it is very practical in much the same way as the excellent DA15 limited is on digital.
The M20 continues to be a solid performer on digital. I did find that sharpness wide open at f/4 was a bit lacking, however there is quite a dramatic improvement from f/5.6 onwards. Perhaps this is the compromise that the lens designers had to make in order to keep the lens so tiny? In my mind, it is worth it! Even though I have listed this point in the cons list, I would consider it almost a non issue.
Another point that is relevant on both film and digital is that the M20 appears to be relatively resistant to flare when compared to some of my other M series lenses. This is a rather useful attribute, as with such a wide lens it is likely that you will have the sun close by for at least some shots. Keep in mind however that I am comparing it against other M series lenses, not modern DA lenses.
On digital the M20 will act like any other K or M lens - this means stop down metering and using manual mode. However in my opinion this is less of a hassle compared to other K and M series lenses of a longer focal length. Don't let it hold you back from using this lens.
One thing about the M20 on digital is that in my mind it is a bit of a strange focal length. Wide but not really wide (I would consider wide on digital 18mm and shorter). Of course this is not the lenses fault, Just something to think about.
On that note, I really do encourage the more adventurous DSLR user to try this lens out on film. I'm sure you will be impressed as it really does come into it's own. Paired with an MX body, you end up with a very compact kit.
In conclusion, I would rate the M20/4 as a 9 on film and an 8 on digital. Here I am rating it as a 9 due to the surprisingly practical nature and excellent optical performance on the 35mm film format.
I have attached a couple of shots taken with scanned Kodak Ektar 100 film. No complaints with contrast, colour or resolution here... I will endeavour to return at some point with some digital images for comparison.
 | | | | | Loyal Site Supporter Registered: June, 2013 Location: Utrecht Posts: 255
1 user found this helpful
| | Review Date: July 4, 2019 | Recommended | Price: $175.00
| Rating: 9 |
| Pros: | Compact, build quality, flare resistance, excellent performance on APS-C | | Cons: | Corners suffer sharpness and fringing at wider apertures | | Sharpness: 9
Aberrations: 8
Bokeh: 8
Handling: 10
Value: 10
Camera Used: K1-II and K-01
| |
This is my standard walk around lens on my white K-01. Together with the M 28 F 2.8 this 20 mm performs extremely well without any serious flaws. Both are very sharp om APS-C, show contrasty colorfull rendering and have great flare resistance. They look cool on the K-01 either with those purple/blue coatings. On Full Frame you have to stop down to F8 or F11 to get good corner performance, at wider apertures the corners suffer a bit. I would rate this a 10 for APS-C and a 8 on Full Frame.
See also my quick & dirty comparrison with other ultra wides at https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/389036-my-old-wide-angles-compared-full-frame.html
 | | | | | Loyal Site Supporter Registered: June, 2011 Location: Texas Posts: 1,446
1 user found this helpful
| | Review Date: July 15, 2015 | Recommended
| Rating: 10 |
| Pros: | Size, image quality, handling | | Cons: | No neon full frame | | Sharpness: 8
Aberrations: 8
Bokeh: 8
Handling: 10
Value: 10
Camera Used: MX, Sony A7
| |
I've stayed with Pentax film bodies where this is truly an ultra wide, and this lens is a winner on them. I didn't bother with it on my K-5. When I wanted wide on digital I used a 21 on my Leica M9 (FF), but the need for an accessory finder is inconvenient. When I got an A7 body to use with my manual Pentax M lenses I was amazed how good this lens is. Yes, there is softness at the extreme edges, but for a FF 20 it is much better than I expected. Recommended!
 | | | | | Senior Member Registered: November, 2011 Location: Los Angeles Posts: 167
1 user found this helpful
| | Review Date: April 27, 2012 | Recommended | Price: $245.00
| Rating: 10 |
| Pros: | Almost a pancake, Bokeh, fun factor X! | | Cons: | Sharpness | | Sharpness: 9
Aberrations: 9
Bokeh: 10
Handling: 10
Value: 10
Camera Used: Pentax ME Super
| |
I shoot film exclusively, so this is a review of the entire lens. Caveat: I'm a total sucker for small lenses. I like to be able to stick a lens in my jacket pocket, another on my camera, and go shoot. If you feel the same, you'll love this lens too.
The bokeh of the M20/4 is really pleasing. I end up taking a fair amount of "impressionistic" photos that are intentionally out of focus or overexposed. These shots end up being pretty good bokeh "test shots":
It's plenty sharp wide open.
 
My only gripes are that with a maximum aperture of f/4, it's a little dark in the viewfinder, and that it's not a 24mm lens. But how stupid is it to criticize a lens for being the wrong focal length.
Hope this helps.
| | | | | Senior Member Registered: March, 2008 Posts: 282
1 user found this helpful
| | Review Date: January 26, 2010 | Recommended
| Rating: 9 |
| Pros: | Color and contrast, size, price | | Cons: | still a little bit of distortion | |
This is one of my favourites, a great little lens. I bought it instead of the DA 21 for a far better price and wasn't dissappointed. It has become my main prime lens on vacation trips (on the K10D).
It produces great colors for landscapes. Sharpness isn't extremely high but fine at f8. Prints at 45 x 30 cm look great. Neither vignetting nor CA noticable to me; good flare control (without hood, that is).
The lens is well built and very handy by its size. Beeing a manual lens doesn't matter much to me for a wide-angle. Once figured out, the exposure setting can be kept almost until dawn :-)
Samples: http://www.flickr.com/photos/chip_de/tags/smcm204/ | | |
;)
;)
