| Author: | | New Member Registered: August, 2013 Posts: 7
3 users found this helpful
| | Review Date: August 31, 2023 | Recommended | Price: $110.00
| Rating: 9 |
| Pros: | Sharp, good saturation, great bokeh, lightweight | | Cons: | Flares sometimes | | Sharpness: 9
Aberrations: 8
Bokeh: 9
Handling: 10
Value: 10
Camera Used: Sony A7R2
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This lens, which is overlooked by many, was a great surprise to me. Tested this lens against the highly regarded Minolta 100mm f/2.5 (late 5 element version), and the Pentax has similar performance.
https://flic.kr/p/2oQdpk7
The Pentax even a bit sharper wide open (also the corners). Great for portraits or as a landscape lens. The Minolta has slightly better control of CA's wide open. CA control of this lens is still much better than the Pentax-M 85mm f/2. Bokeh is great.
On top of that, the lenses weights is only twothirds of the already tiny and compact Minolta new MD 100/2.5, and has better build quality. Because the quality of Pentax-M is somewhat of a mixed bag, the lens is practically ignored by most and can be found at a modest price.
 | | | | | | | Pentaxian Registered: December, 2007 Location: Pacific Northwest Posts: 325 | | Review Date: March 25, 2023 | Recommended | Price: $79.00
| Rating: 10 |
| Pros: | Sharp, lighweight, compact lens with excellent flare control | | Cons: | A bit of longitudinal CA, but not bad given that it is not an APO lens. | | Sharpness: 10
Aberrations: 8
Bokeh: 9
Handling: 10
Value: 10
Camera Used: S5 (full frame) and K-70 (APS-C)
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I have tried a few of the short M-series teles, including this lens, the M120/2.8 and the M135/3.5. In my experience this one is easily the best, particularly on full frame. It is surprisingly sharp across the frame when wide open, and becomes extremely sharp stopped down. It is very resistant to flare, which is a real advantage of Pentax lenses from this era. So many older lenses from other manufacturers flare like crazy if you dare to put the sun or a bright light in the frame. This lens also has VERY nice bokeh, except for just a bit of longitudinal chromatic aberration ("bokeh fringing") when shot wide open, although even in this regard it compares well to other similar lenses. It is also TINY and lightweight. The size and weight, combined with it's silky-smooth focus ring, make it a joy to use. It's one of my favorite lenses of all time. It's also one of the least expensive lenses I've ever purchased. It's a real hidden gem and a stunningly good value!!
| | | | | New Member Registered: May, 2014 Location: Ogre Posts: 9 | | Review Date: May 23, 2022 | Recommended | Price: $100.00
| Rating: 10 |
| Pros: | sharp, bright, value, compact | | Cons: | no | | Sharpness: 10
Aberrations: 9
Bokeh: 9
Handling: 10
Value: 10
Camera Used: PENTAX K3
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Very very sharp and compact lens. Easy to put in your pocket. Feels very good buit. Important to use lens hood on a sunny day. Bought it a few years ago on Ebay for 90 euros. This lens is a much more valuable.
 | | | | | New Member Registered: March, 2022 Posts: 2
1 user found this helpful
| | Review Date: March 24, 2022 | Recommended
| Rating: 10 |
| Pros: | Supersharp, a dream to handle | | Cons: | | | Sharpness: 10
Aberrations: 9
Bokeh: 7
Handling: 10
Value: 10
Camera Used: Fujifilm GFX50R
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I've had this lens since new in the 70s but I don't remember what it costed then. I've taken up photography again after many years of low interest and WOW, what a lens this is!
Recently I bought a used GFX50R and tried the old Pentax and to my surprise it worked super fine. No vignetting that I have seen and really sharp when I have used it for landscape pictures. It's not easy to distinguish which images are from the GF100-200 @ 100mm and which are from the Pentax-M 100mm f2.8.
| | | | | | | New Member Registered: February, 2019 Posts: 15 | | Review Date: November 2, 2020 | Recommended
| Rating: 8 |
| Pros: | Just like a 135mm M Series | | Cons: | Too expensive | | Sharpness: 9
Aberrations: 8
Bokeh: 7
Handling: 10
Value: 8
Camera Used: Film
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If you need a short telephoto (what many people convince themselves they need for portrait work) then this is a good one, but it is exactly the same image quality as an M series 135mm but costs four or five times as much. Slightly smaller and lighter, though. And don't think all it's useful for is portrait work, as it's as versatile as any 85mm, 105mm or 135mm lens. Alternatively, use a 50mm lens and just walk a bit closer.
| | | | | New Member Registered: June, 2020 Posts: 2
1 user found this helpful
| | Review Date: July 27, 2020 | Recommended | Price: $120.00
| Rating: 8 |
| Pros: | Crazy sharp from F5.6, excellent contrast | | Cons: | Nervous bokeh sometimes, weak at F2.8 | | Sharpness: 8
Aberrations: 8
Bokeh: 6
Handling: 9
Value: 8
Camera Used: EOS 60D
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Above F5.6 this is crazy sharp lens, high contrast and great resolution.
Using it for close up (macro tubes) it destroys Tair 11A, Jupiter 37A, CZJ Sonnar and Pentax-K 135/2.5.
 | | | | | Pentaxian Registered: April, 2009 Location: Madrid, Spain Posts: 10,897 | | Review Date: July 21, 2020 | Recommended | Price: $130.00
| Rating: 8 |
| Pros: | Compact, very well built, reasonably sharp | | Cons: | Not too sharp wide open, images lack a bit of punch | | Sharpness: 8
Aberrations: 9
Bokeh: 8
Handling: 9
Value: 9
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I bought this in lieu of a faster 85mm lens, though not too long after I got the M 85mm f/2 and then the 100mm didn't get much use as the 85mm is a really superb lens.
The lens is very well built but not too heavy, exactly what you would expect of an M. Focusing is very smooth and the aperture ring clicks nicely. The aperture goes straight from f/2.8 to f/4, a whole stop, one of the little annoyances common with older lenses.
Wide open this lens is just sharp enough to use on digital. At f/4 it's considerably better and it improves as expected after that. The biggest problem with this lens is that images from it tend to be a bit low contrast and lacking in punch, though I feel that this contributes a bit to a subtlety of rendering that you don't often get with newer optics. Contrast can be increased in post processing but it's not the same as getting contrastier results straight away.
Compared to it's nearest neighbours in the M line, the 85mm f/2 is superior in every way except for the blue fringing it produces, and the 120mm f/2.8 is just superior in every way, though it's a different focal length so may not be suitable for the same photos. Compared to the Takumar 105mm f/2.8 the M is much sharper at wider apertures, though the Takumar is really, really silky smooth to operate (at least my copy is) so it's a pleasure to use. I also have a Sigma 105mm f/2.8 macro and that's optically far better than the M - sharper and with better contrast, rendering and bokeh.
The strength of this lens lies in the aforementioned subtlety of rendering and the soft colours that it brings.
If you're looking for a manual lens in this focal length then this one is adequate but there are slightly better options if you don't need it to be exactly 100mm and you want a modern (bright and contrasty) look. If you like a more "vintage" rendering then this might be just the lens for you.
Some sample images:
Waiting by Jonathan MacDonald, on Flickr
IMGP6349a by Jonathan MacDonald, on Flickr
Segovia by Jonathan MacDonald, on Flickr
IMGP1039a by Jonathan MacDonald, on Flickr
IMGP3924a by Jonathan MacDonald, on Flickr
| | | | | New Member Registered: March, 2019 Posts: 2
1 user found this helpful
| | Review Date: July 21, 2020 | Recommended | Price: $100.00
| Rating: 9 |
| Pros: | size, build quality, IQ | | Cons: | None to sepak of | | Sharpness: 8
Aberrations: 8
Bokeh: 10
Handling: 10
Value: 9
Camera Used: Sony a6000, Pentax me super
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This is a lovely lens. Typical of all m lenses, it is very small and light for the focal length. In fact, it is barely any longer than my Pentax m 50mm f1.7 lens. Sharpness and IQ wide open are decent enough although not up to the incredible standards set by the Nikkor 105 2.5. Sharpness at infinity when using this as a telephoto rather than portrait lens is ok but not outstanding.
The bokeh is lovely and smooth, colours typically Pentax quality and the build quality outstanding. It feels built to last. This is such an easy lens to use because it is small and light. Great for street photography as people don't realise you have a short telephoto lens on the camera with great reach. Definitely recommended.
| | | | | Junior Member Registered: July, 2017 Posts: 42
1 user found this helpful
| | Review Date: May 14, 2020 | Recommended | Price: $25.00
| Rating: 9 |
| Pros: | Inexpensive, very sharp, low CA | | Cons: | None | | Sharpness: 9
Aberrations: 8
Value: 10
Camera Used: Pentax K-3II
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I have been using this lens on a K-3II, strictly for astrophotography. For that purpose it is one of the best lenses I have. When it is stopped down to f/4, it is very sharp and the CA is relatively low for a non-ED lens. Here is an astrophoto taken with it (tracking by Astrotracer):
 | | | | | Pentaxian Registered: November, 2018 Posts: 586
3 users found this helpful
| | Review Date: October 3, 2019 | Recommended
| Rating: N/A |
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 | | | | | Loyal Site Supporter Registered: June, 2013 Location: Utrecht Posts: 255
2 users found this helpful
| | Review Date: September 9, 2019 | Recommended | Price: $80.00
| Rating: 10 |
| Pros: | Light, compact, sharp and contrasty, super sharp stopped down | | Cons: | Some purple fringing, easy removable | | Sharpness: 9
Aberrations: 8
Bokeh: 10
Handling: 10
Value: 10
Camera Used: K1ii, K-01 and film
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I bought this long time ago for fl 100,- ( no euro's that time) and it was my most used short tele / portrait on film. This lens also shines on digital. Always use a hood to avoid flaire. This lens is well build, light weight, decent sharp already wide open (though little contrast), has superb color reproduction and at from F4 - F8 nice contrast. I compared this with the DFA 100 macro 2.8, you can find it here: https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/392245-my-...dern-dfas.html
The DFA is sharper wide open, frings less and produces more contrast. But the difference is minor.
If you can grab it for little, you won't be disappointed. It's not a macro b.t.w.. If you own it for portraits, you can save the money buying a DFA for that purpose.
Digital on K-01:
Scanned older color negative:
 | | | | | Forum Member Registered: May, 2018 Location: NYC Posts: 80
5 users found this helpful
| | Review Date: November 11, 2018 | Recommended
| Rating: 9 |
| Pros: | colors, bokeh, focal length, rendering | | Cons: | none for the price | | Sharpness: 9
Aberrations: 8
Bokeh: 9
Handling: 9
Value: 10
Camera Used: Sony A7III
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I did not list the price as I picked this up at a yard sale for $20 and that would skew the prices.
I got this a few years back not knowing what it was - I did not have a camera at the time to use it on.
I thought it looked like a good lens and it had the original case and caps so I picked it up with the idea of using it some time in the future.
I was finally able to try it this year when I got the Sony A7III.
I used the K&F Concepts PK-NEX adapter and was amazed at the results of this lens right away.
In fact this was the lens that got me into seriously considering other vintage manual lenses to use with the A7III (now I have mild LBA).
The 100mmm length is actually quite handy once you figure out where you need to be to get an effective shot.
Not surprisingly, its like having a slightly longer 85mm and shorter 135mm with a combination of what those two focal lengths offer - the DOF of the 85mm for portraits and the reach of the 135mm.
Colors are rendered very nicely, images are sharp and low light images are good (at least they are with the A7III which is an excellent low light camera).
Bokeh is pretty easy too - it is smooth and pleasing.
Great lens!
Here are a couple of shots I first took with this lens:
 | | | | | Veteran Member Registered: March, 2013 Location: Yukon Posts: 516
3 users found this helpful
| | Review Date: October 23, 2018 | Recommended
| Rating: 10 |
| Pros: | IQ in general, Sharpness, colors, small and light | | Cons: | Can cause LBA? | | Sharpness: 10
Aberrations: 8
Bokeh: 8
Handling: 9
Value: 10
Camera Used: MX, K10D, K20D, K-5II, K-1
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Ok, so this lens kind of changed everything for me. Found at a garage sale, and not putting in my price here because it was unrealistically low. I knew nothing about this lens, but for less than the price of a pint, hard to resist.
I have used this lens mainly with digital, though excellent with film too. On digital it seemed a world above my M50/1.7 and M28/2.8. Not sure what the magic of this lens might be - great combo of sharpness and color? Compact easy handling? Someone had mentioned using all auto-focus lenses other than this - because somehow this particular lens seems to focus automatically anyway?!? Ok, not quite, but....
Ok, who knows what it is, but if I'm unhappy with photos I'm taking, I put on the M100/2.8 and my day gets better. Not sure why.
Yes there's some PF, and sometimes colors seem too bright and too strong? But...
And then I think this caused a bit of LBA... Could other lenses change my day the way this one can?
Yikes, hadn't meant to write a new-agey review! Will add more sometime...
| | | | | New Member Registered: June, 2017 Posts: 3
1 user found this helpful
| | Review Date: June 16, 2017 | Recommended | Price: $100.00
| Rating: 9 |
| Pros: | Nice bokeh and usability | | Cons: | none really | | Sharpness: 9
Aberrations: 8
Bokeh: 9
Handling: 10
Value: 10
Camera Used: Samsung NX1
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I'm using this on a Samsung NX1 with the official NX to PK adapter. Fully manual, but works great. Great lens for outdoor portraits and landscapes. Photos come out sharp enough and very adjustable in lightroom. I also have the 135mm, but prefer using this 100mm more. Photos edited to taste in Lightroom.
  | | | | | Site Supporter Registered: October, 2008 Location: Vancouver, Canada Posts: 8,091
4 users found this helpful
| | Review Date: February 18, 2017 | Recommended | Price: $134.00
| Rating: 8 |
| Pros: | Well built and good handling. | | Cons: | Could be sharper, minimum aperture of f/22 | | Camera Used: Pentax film bodies (K1000, KM, KX, K2, K2DMD, ME, MX, LX, Super A, P50)
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The M100/2.8 was released in 1977 and was a direct “miniaturized” replacement for the K105/2.8. The M100/2.8 was in production until 1984, when it was replaced by the A100/2.8.
Optics:
Typical “M” series optics compared to the “K “series lens it replaced. Pretty good, but nothing outstanding at any aperture.
Focal Range:
100mm is a nice focal length on FF for portrait or short telephoto work. Though it’s sad with the release of the M100/2.8 Pentax stopped producing a 105mm option for the first time since the late 1950’s.
Build:
Excellent all metal build in a smaller size & weight than its K Series predecessor.
Usage/Handling:
Excellent handling for an “M” series lens, mostly due to it being a short telephoto. The M100/2.8 also has a great distance scale and is easy to manual focus or adjust the aperture. Very nice compact telephoto lens to travel with.
The M100/2.8 uses a 49mm round plastic clip-on hood labelled: “SMC PENTAX 1:2 85mm 1:2.8-4 100mm”. This detachable lens hood will offer better protection than the smaller built-in hood on the A100/2.8. The M100/2.8 also had a dedicated hard lens case which also held the hood or you can use the shorter Pentax soft lens case from that period.
Speed:
F2.8 is an average speed for a telephoto lens in the 100mm to 135mm focal range. The 85mm lenses tended to be faster and of course more expensive. The 100mm/105mm lenses were the slower more affordable portrait option.
The M100/2.8 vs my other similar FL short telephoto primes:
I also own the K105/2.8 which is sharper at every aperture compared to the M100/2.8. The M100/2.8 is as well built & handles the same as the K105/2.8 and has a slightly better minimum focusing distance of 1 meter compared to 1.2 meters for the K105/2.8. The K105/2.8 has a better minimum aperture of f/32 than the M100/2.8’s f/22. I rated my K105/2.8 a 9.5 and the M100/2.8 gets an 8.5.
Summary:
Overall the M100/2.8 is an excellent short telephoto/portrait lens that is perfect for travelling due to its smaller size. But it’s not in the same league as its older brother the K105/2.8
Price:
I bought the M100/2.8 off eBay. It was in excellent + condition and came with the lens hood.
Sample shots taken with the M100/2.8. Photos are medium resolution scans from original slides.
Camera: KM Film: Fuji Velvia 50 ISO: 50
Camera: ME Film: Fuji Provia 100F ISO: 100
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