| Author: | | 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:
 | | | | | | | Site Supporter Registered: October, 2008 Location: Vancouver, Canada Posts: 8,090
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
 | | | | | New Member Registered: March, 2009 Location: Copenhagen Posts: 10
4 users found this helpful
| | Review Date: January 12, 2015 | Recommended | Price: $90.00
| Rating: 9 |
| Pros: | Small, light, well built, sharp, nice bokeh, cheap | | Cons: | Purple fringing at full aperture against the light, a bit long for portraits on digital camera | | Sharpness: 9
Aberrations: 7
Bokeh: 10
Handling: 10
Value: 10
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Despite this lens doesn't have automatic aperture (for those using it on a digital body) I have given it a 10 for handling due to the fact that it's diminutive size combined with light weight and the buttery-smooth focus ring makes the handling exquisite and for me I like to use it on 2.8 due to the great bokeh for portraiture, so I havn't really missed the "A"-setting. Suprisingly I havn't been able to find many images online taken with this lens so I have attached some images that I have shot with a K5 - making it a 150 mm effectively but still with the size of a 50 mm standard lens! This lens though, is abit challenged from purple fringing when shooting against strong light. This lens is a very inspiring little gem! Enough words, I will let the images will speak for themselves 
   
  
 | | | | | New Member Registered: December, 2012 Posts: 7
4 users found this helpful
| | Review Date: January 10, 2013 | Recommended | Price: $120.00
| Rating: 10 |
| Pros: | Sharp, Light, Easy to Handle, Wonderful colors | | Cons: | none | | Sharpness: 10
Aberrations: 9
Bokeh: 9
Handling: 10
Value: 10
Camera Used: Olympus OM-D E-M5
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I just picked up a mint copy of this lens on fleabay and it is a marvel. So light and and so sharp at all apertures. I have the Pentax-M 100mm f4 Macro and two copies of the Pentax-A 50mm f1.7 and can offer some comparative analysis. All three are very sharp, light, and easy to use manual lenses on the Olympus OM-D E-M5. The camera does not have peak focusing in the version 1.5 firmware but it is still very easy to get accurate focus on that camera with any of these lenses. In terms of sharpness I would rank them this way:
1. 50mm f1.7
2. 100mm f.28
3. 100mm f4
I use the 50mm with extension tubes and it is sharper at 1:2 than the 100mm f4. Its not as convenient to use and the focus distance is fine for flowers and other things that don't move, but the detail and contrast (with a hood) are better. For portraits all three are extremely sharp. Photograph someone over the age of 50 and they will not be pleased with the level of detail. But beyond portraits and street photography, at longer distances, the differences in the lenses become clear. The f1.7 and the f2.8 can do both short range and long distance. I find the f4 macro not well suited for landscapes on my camera. Near or at infinity and the photos show low resolution in trees and distant objects. The 100 f2.8 does not share this limitation. It is an all around useful lens.
When I travel, I will take the 100mm f2.8 in my bag. It is so short and light it will be perfect for candid street portraits as subjects will never suspect they are being photographed with such a diminutive lens on a little camera far across the street. It will get use indoors at concerts and events. And I will use it for focused landscapes. It is a wonderful little lens that continues my love affair with legacy Pentax glass.
| | | | | | | 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: November, 2018 Posts: 585
3 users found this helpful
| | Review Date: October 3, 2019 | Recommended
| Rating: N/A |
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 | | | | | 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: September, 2016 Posts: 3
3 users found this helpful
| | Review Date: October 30, 2016 | Recommended | Price: $50.00
| Rating: 10 |
| Pros: | Quality through and through | | Cons: | Can't think of any | | Sharpness: 10
Aberrations: 9
Bokeh: 8
Handling: 10
Value: 10
Camera Used: K-30
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Metering and auto white balance is spot on with my K-30, which isn't to take for granted with legacy lenses. No need to dial in any + or - EV.
So much fun to shoot with this lens, so small for this focal length, yet so well constructed. Focuses like a dream and focus throw is not too long which makes for fast shooting even though it is a manual lens. Focuses close enough that it's even usable indoors in spite of the long focal length.
Still sharp enough wide open but with some very slight PF in harshly lit areas. Immaculate image quality stopped down from F4 onwards. Great contrast and rendering. Very nice out of focus areas. Faultless prime. Price I paid for an excellent copy is laughable. Some lenses you know you will never get rid of, and this is one of those for sure.
Downscaled original sample + 100% crop, shot at F5.6 if I remember correctly. Impressed with the sharpness which can be seen in the rendering of the window frame, where the finely corrugated stone border is resolved without any issues.
  | | | | | New Member Registered: June, 2013 Posts: 18
3 users found this helpful
| | Review Date: October 6, 2016 | Recommended | Price: $50.00
| Rating: 10 |
| Pros: | Great image quality in small package | | Cons: | I wish it has more aperture blades. | | Sharpness: 10
Aberrations: 9
Bokeh: 10
Handling: 10
Value: 10
Camera Used: Sony a7
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This is my main portrait lens on my a7. My copy is in great condition, like new, the glass was incredibly clean and cosmetically in perfect condition. The focus grease was a bit dry, so I relubed it and now it really is a joy to use. The lens is very small, with is a big plus.
I was astonished when I saw the first portraits. I didn't expect such a great image quality. At f2.8 is very sharp, but not excessively sharp, and contrast was a bit flat. But microcontrast is at a very good level at this point. It vignettes a bit. Very good for portraits. At f2.8 it has a bit of purple fringing, but not so much! When stopped down it becomes great. At f5.6 sharpness in incredibly high, and focusing at infinity gives excellent sharpness across the frame on a FF camera. Very impressive. Bokeh is very beautiful and smooth at all apertures and seems to resist flare very well.
The six aperture blades make a smi-circular shape until f5.6, but I really wish it had more of them. 8 blades would be perfect.
I recommend this lens!
| | | | | Veteran Member Registered: September, 2006 Location: Denver, CO Posts: 10,685
3 users found this helpful
| | Review Date: December 15, 2008 | Recommended | Price: $118.00
| Rating: 9 |
| Pros: | great combo of focal length, speed, IQ, size, build quality, and cost | | Cons: | much more purple fringing in very high contrast situations than other lenses | |
As I said in my summary above, this lens provides a fantastic value proposition - a really useful focal length (both on 35mm and APS-C, if for different reasons), decent speed, fine IQ, incredibly compact, solid build. And it's a bargain - I paid a little over $100 for mine, but also I bought one for my wife for a little *under* $100.
One of the things I do most is concert photography - digital - and I've decided this lens is as close to perfect a single prime lens as I could hope for. Wide open, I'm pretty sure it is outresolving what my (K200D) sensor can muster at the high ISO levels typical of concert photography. The focal length is pretty much ideal for isolating performers from a vantage point near to the front as you'd likely be if you're at least somewhat serious about it. It could work as a portrait lens outdoors or for really tight head shots, and it's just long enough on digital to feel like a "real" telephoto lens in other situations as well (if, obviously, not a wildlife lens). On 35mm, it would make a great portrait lens or for certain types of street candids, and would also work for concert photography if you like a little space around your subject or intend to shoot from right on stage.
So for me, it's pretty tough to beat on paper just based on specs, assuming it takes a picture at all. But I suppose most people will concentrate more on IQ :-).
Below, I'll link to a comparison against a couple of other M series telephoto lenses. But for now, I'll summarize that by saying it's the sharpest of the bunch at f/2.8. At high ISO, it's probably more resolution than my camera can use, and at lower ISO levels, I can clearly see my reflection in the eye of a portrait of my cat.
Stopped down, it's clearly at least as good as a consumer zoom like the 50-200 or Tamron 70-300. And comparisons posted by "Douglas of Sweden" on the SLR Lens forum show the optically-identical "A" version to hold up quite well against the extraordinarily well-regarded DA* 50-135 wide open. But I do suspect the 50-135 would win more clearly at f/5.6 or f/8, as the M100/2.8 doesn't actually perform dramatically better at these apertures compared to f/2.8. The resolution tests published by Yoshihiko Takinami show it not reaching maximum resolution until f/16, and while I haven't done any formal testing, this does seem consistent with what I've noticed.
Because I use the lens primarily for low light concert photography, I did notice the Achilles heel of this lens for quite some time. But shooting high contrast subjects wide open in bright sun, it has more purple fringing than any other lens I have used. Not that shooting high contrast subjects wide open in bright sun is a particular common thing to be doing. That fact that the lens lacks the built-in hood of the M120/2.8 and M135/3.5 is a disadvantage, too.
The bottom line for me regarding IQ is that at f/2.8, it's competitive with just about anything else, it seems, which is saying a lot considering the price and the size. At f/8, it's competitive (at least) with a consumer zoom, if perhaps not with a DA* or a macro. And at f/16, it's probably competitive again with any high end lens that started to become diffraction-limited at f/8 or f/11.
Here is my comparison against the M120/2.8 and M135/3.5:
https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/137220-shootou...5-3-5-a-2.html
My conclusion from a few posts later in the thread:
 Quote: The 100 is the sharpest when comparing images at constant magnification (by a small margin over the 120 and a larger margin over the 135). And not that the others are particularly large or heavy (they aren't!), but the 100 is *noticeably* smaller and lighter. However, it has the most purple fringing by far, it lacks a built in the hood, and it can't blur a background to the same extent as the other two. It is the most generally useful portrait focal length of the three, but it has the least "reach". It is not too hard to find with a little patience, and it usually goes for $100-$150. Again, given what you're getting for the money, it's a really great package!
Sample concert shot at f/2.8:
 | | | | | 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:
 | | | | | Veteran Member Registered: July, 2014 Location: Nagoya Posts: 577
2 users found this helpful
| | Review Date: July 31, 2016 | Recommended | Price: $180.00
| Rating: 10 |
| Pros: | Sharpness/clarity, size, build, handling | | Cons: | None worth mentioning | |
Sharp and contrasty pictures from f2.8, compact, classic M series quality, ideal for portraits, flowers and longer street shooting (I use it for street with black and white film a lot, and it really shines).
Even for £100 in Exc+ condition I think it's a bargain. Definitely recommended. Get a cheap 49mm tele hood for best results.
K1000, Fomapan 100, f4:
 | | | | | Pentaxian Registered: November, 2011 Posts: 4,310
2 users found this helpful
| | Review Date: December 19, 2011 | Recommended
| Rating: 10 |
| Pros: | Compact, light, sharp, well-made | | Cons: | Manual focus | | Sharpness: 10
Aberrations: 8
Bokeh: 8
Handling: 8
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This was a favorite lens for years on film with the LX, and now sees occasional use in digital on my K-x. There, I use stop-down metering with the green button, in M mode. For good meter readings on landscape, I've found a 50% sky/50% land mix to give the best results under most conditions (where the M50/1.4 works better with a 33% sky/67% land mix).
The lens has all the usual M-series characteristics: compact, light, sharp, solidly made. It is not as directly contrasty as many Pentax lenses, but the contrast is easily boosted in PP.
Here is a pair of MTF charts, at f/2.8 and f/5.6. I usually shoot this lens at f/5.6, where both the 40 lp/mm curves stay above the 50% level right out to the edge of the APS-C frame just shy of the 15mm radius.
A sample from the street:
Center crop:
Edge crop:
 | | | | | Site Supporter Registered: October, 2009 Location: Denver, Colorado Posts: 2,030
2 users found this helpful
| | Review Date: October 10, 2011 | Recommended | Price: $110.00
| Rating: 9 |
| Pros: | Size, Focusing, Sharpness, Bokeh, Everything! | | Cons: | None, for a MF non-auto lens | | Sharpness: 9
Aberrations: 9
Bokeh: 10
Handling: 10
Value: 10
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This little lens is a gem and one of my all-time favorites. The focus action is slightly "heavy" and dead accurate, like all the good copies of M lenses. It is the gold standard for any focus ring feel, no drift or slop, you just nail the subject and click the shutter, no muss, no fuss.
I find the 100mm (or 150mm in digital) perfect for street candids, casual shooting and short tele work. It is small and unobtrusive, not a big honker that shouts "I'm taking YOUR picture!" with the resultant nervous and self-conscious look from the subject.
F2.8 is great for indoor or dim lighting, concerts and social events. It can be slightly soft wide-open, especially at the edges, but this is easily corrected or cropped.
It is prone to flare, with the resulting loss of contrast unless you use a quality lens hood. I tried an after-market 49mm hood that extends 18mm from the filter ring and it still showed slight flare/glare in extreme side-lighting conditions. Next I went to a hood that extendes a whopping 32mm (so much for "unobtrusive"!) and all the flare was gone. No sign of vignetting or fall-off so far, even though this hood is marketed as for the 150mm or 200mm teles.
And the bokeh! Oh, my, it is simply spectacular. Very painterly and smooth in the wider apertures with wonderful highlight rings reminiscent of a mirror lens but less obtrusive and much smaller. With this lens at f2.8 to 4.0, you can truly "Paint with light" if you are so inclined.
A very nearly perfect short tele.
| | | | | Pentaxian Registered: June, 2010 Location: North Zealand, Denmark Posts: 1,516
2 users found this helpful
| | Review Date: July 8, 2011 | Recommended | Price: $50.00
| Rating: 10 |
| Pros: | Sharp, fast, well built, compact and light | | Cons: | none whatsoever | |
I bought this lens together with an SMC 35/3.5 ("K" version) and some more inferior stuff at a lump sum of USD 110 - so the 50 dollars are my assed "partial value" of that deal.
Perhaps a bit mad to give any lens maximum rating and 9.5 would rather be more appropriate - if only permitted. Of course, this lens has neither A-functionality, nor autofocus - but when you buy a purely manual lens, you do know what you are NOT buying and paying for and thus, it would be unfair to let that influence one's rating. (Or, that is a least how I feel about it).
Anyway, this lens has taken me with surprise: Not only sharp but very sharp even wide open, excellent colur rendition, very easy to focus, light and compact, yet with a reassuring feel of good solid workmanship.
I have read about potential purple fringing issues in high contrast situations, but I have yet to discover those myself. I feel lucky with this deal.
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