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SMC Pentax-M 40mm F2.8

Reviews Views Date of last review
38 156,525 Fri December 6, 2019
Recommended By Average Price Average User Rating
79% of reviewers $94.15 7.86
SMC Pentax-M 40mm F2.8

SMC Pentax-M 40mm F2.8
SMC Pentax-M 40mm F2.8

Also known as the "pancake," this is the smallest SLR lens that Pentax ever produced. It includes all the features of any other M lens.

In 2006, it was superseded by an even smaller DA version, but that version did not feature an aperture ring.

SMC Pentax-M 40mm F2.8
©, sharable with attribution
Image Format
Full-frame / 35mm film
Lens Mount
Pentax K
Aperture Ring
Yes (no A setting)
Automatic, 5 blades
5 elements, 4 groups
Mount Variant
Check camera compatibility
Max. Aperture
Min. Aperture
Min. Focus
60 cm
Max. Magnification
Filter Size
49 mm
Internal Focus
Field of View (Diag. / Horiz.)

APS-C: 39 ° / 33 °
Full frame: 57 ° / 48 °
Hard case HA-90B
Lens Cap
Plastic clip-on
Weather Sealing
Other Features
Diam x Length
63 x 18 mm
110 g
Production Years
1976 to 1984
Engraved Name
smc PENTAX-M 1:2.8 40mm
Product Code
User reviews
Lens was sold without hood. The folding rubber hood RH-A49 fits
Manual FocusAperture RingFull-Frame SupportDiscontinued
Price History:

Add Review of SMC Pentax-M 40mm F2.8
Sort Reviews by: Date | Author | Rating | Recommendation | Likes (Descending) Showing Reviews 31-38 of 38
New Member

Registered: April, 2009
Location: Poland
Posts: 1
Lens Review Date: April 16, 2009 I can recommend this lens: Yes | Price: $150.00 | Rating: 9 

Pros: Great on film camera
Cons: Do not use with a DSLR

I love the pancake lens when I use it with an old ME Super for BW photography. I find the 40mm focal length very useful on film as it is wider than the 50mm standard and yet it has little distortion, less than other wider angle primes (28, 35).
It is so small when attached to my ME Super body that I can carry it with me most of the time.
I wouldn't recommend using it with DSLR though. It is hard to get accurate focus with small viewfinder of a DSLR (compare K10 and ME Super's viewfinders and you'll know what I mean).
Because of the crop factor it's great focal length is not an advantage on DSLR's
I often shot stepped down to f 8 or so and the photos are really sharp.
Built quality is great and after so many years of usage it still works like a charm.
Senior Member

Registered: September, 2008
Location: Norway
Posts: 127
Lens Review Date: September 17, 2008 I can recommend this lens: No | Price: $70.00 | Rating: 5 

Pros: very small, good build quality, fun ?
Cons: could be sharper

The original pancake is a classic. Once again it seems like I did a good buy. It was bundled with a couple of other lenses, but if I split it up it was somewhere around $70 for this one.

It's a bit fun to use, and I don't have a problem with focusing. The focus ring is small, but well defined for you fingertips. To me it feels like it very quickly gets into hyperfocal range. Build quality seems good with metallic construction like other m-lenses.

It really looks sexy on my MG film camera - they are a great pair. However I don't think it is quite as good as a lot of the other m-lenses on a modern digital SLR. I have used it on a K100D, and produced a couple of nice pictures in the golden hour with results a bit like a typical 70s photographic wallpaper

It's fun and easy to find for sale, but don't put too much work into getting one. It feels a bit harsh to say that I don't recommend it. It's not bad, but unless you want it for it's small size, there are probably better lenses out there to spend your money on.
Senior Member

Registered: January, 2008
Location: Bondi, Australia
Posts: 206
Lens Review Date: January 29, 2008 I can recommend this lens: No | Price: $70.00 | Rating: 4 

Pros: small, good optically stoppeddown a bit
Cons: hard to use focus ring

Like nearly all Pentax lenses, it is soft wide open and hits its straps down 2 stops. I found it very hard to use the focusing ring - too small. Quite credible optically, good replacement of a 50mm as a standard lens for those that like it a bit wider. Have a 35 f/2 , so sold off the 40mm while it stil had its cult status. The cult status is probably only for the extreme compactness. In general, I have found the M lenses to be not as good as the K lenses optically.
Veteran Member

Registered: November, 2006
Location: Belgrade
Posts: 656

1 user found this helpful
Lens Review Date: December 26, 2007 I can recommend this lens: No | Price: $140.00 | Rating: 6 

Pros: Small, excellent focal length on film, good for MX/ME/ME Super
Cons: Low corner sharpness below f/5.6 (see the review)
Sharpness: 7    Aberrations: 7    Bokeh: 7    Handling: 4    Value: 5   

I mostly agree with previous comments: the lens is overrated and price should not go over $100 in my opinion.

The major negative aspect is that M40/2.8 does not reach very good corner sharpness until f/5.6 (tested with *istDS) but it is not bad either. Note that center sharpness is good to excellent at all apertures, while I would rate corner optical performance as average at apertures below f/5.6. At f/5.6 corner sharpness improves drastically and the lens performs very well over the range f/5.6-f/16 on both DSLR and film SLR (tested with Pentax MX and ILFORD XP2 film).

However, I would not recommend this lens for use with DSLRs. If you are looking for a compact DSLR lens consider DA40/2.8 Limited. My main reason for getting M40/2.8 is to use it with MX if I decide to shoot a roll of film without carrying my other M lenses: 40mm is very convenient "universal" focal length on film, the lens itself is much smaller and lighter than M50/1.4, and performs very well stopped down which is not a problem at all if shooting in normal daylight conditions (I keep it at f/8 most of the time).
Giveaway winner!

Registered: December, 2007
Location: beantown
Posts: 944

1 user found this helpful
Lens Review Date: December 14, 2007 I can recommend this lens: Yes | Price: $118.99 | Rating: 9 

Pros: Small, fits in most of my pockets, sharp enough.
Cons: not as good as my 50mm, element delaminated.
Sharpness: 9    Aberrations: 8    Bokeh: 9    Handling: 8    Value: 9   

LpMM nit-pick... nonsense:
The test I ran long ago scored about 46lpmm at average in f4. The corners only 37lpmm and the high of 48lpmm... What does that mean? Nothing in real life.... the lens seems to do well enough and sure, not a stellar lens, it still get the job done.

Rear element Issues:
The original test was on my pre-repaired lens. Soon after the lens test it developed a de-lamination problem and grew from the sides in on the rear lens group.

Post repair:
I started to use it again and with newer emulsions as well a the digital (K20D) and found that the pictures were much better than I recalled. The cement was a recommended type for lenses and claimed not to change the dynamics of the lens to any degree that could be noticed. On the plus sides I'll disagree!

Originally a so-so score, I've found it seemingly a bit more higher.
The center was about 55-56 and the corner on a full-frame is 39-45lpmm, this is from the Ektar and TMax film in the test... sorry, no Tech-Pan.
On a APS-C format, the test is a little tricky to compute for results, but the numbers are similar at center... 52-55 lpmm and the corners 49-52. Using film style test on a digital is difficult to do and I don't have the standard digital targets so take this with a grain of salt.
(compared to: M50/1.4 @ f2.8 and a top score of 61-64lmpp @center / 52-54 @ corner)
And now, what does these numbers mean? ...nothing... It still is a nice lens for its size.

Wide open the lens is good for most applications and still is a bit mushy, at f4.0 the lens is as good as many lenses, at f8 it is harder to tell one from another lens in sharpness. I tested at up to f8 and it seems to hugged near the acceptable results and it seems that f11 to f22 your getting less contrast.

What is really important in all?
Post repair, a better utility lens than one would think.
Original form with no de-lamination problems, it is a good value due to the size. A slip into the rain coat or any medium large pocket or narrow bag.

Colors are very good and the glare resistance is very good in more general situations, but you should shade in high brightness situations.

The one big gripe is the weak rubber grip. One thin strip of rubber prone to damage and near impossible to replace with the same. A nice suggestion of using an equivalent size rubber O-ring.

The DA 40mm is a sort of successor, but only in the APS-C format... not had the chance to test it.

Summing it up:
Reality is that most versions out there will not have a major optical repair applied to it. So the thing to remember is that this lens is mostly a small handy lens and it is a super match to any of the M-Series film bodies when small is what you need. Remembering that it functions much like a "Snap-Shot" lens, I'll forgive the short comings because its the compact size that I am happy about. Similar or smallish might be a M28 or M30, but the M40 fits in my pocket... jacket pocket.
Site Supporter

Registered: March, 2007
Location: Los Angeles, CA
Posts: 460
Lens Review Date: May 5, 2007 I can recommend this lens: Yes | Price: $80.00 | Rating: 8 

Pros: light weight, super compact, good image quality
Cons: can be hard to use because of its size, not the sharpest lens

I really like this lens, even though it's not the sharpest and there's a good amount of purple fringing wide open.

It makes my K100D very compact and easy to carry around. I also like the 40mm focal length, which is a comfortable length for me to take pictures of people. A lot of Pentax users seem to like this lens for street photography because it makes their cameras look less invasive.

My copy of the lens is pretty worn, but it still works great. I liked it enough that I bought the DA 40mm Limited so I can have autofocus again. Comparing the two, I like the colors of the DA 40mm better, but it also seems to be worse with fringing in high contrast environments.
Veteran Member

Registered: September, 2006
Location: Toronto
Posts: 960
Lens Review Date: February 7, 2007 I can recommend this lens: No | Price: $250.00 | Rating: 5 

Pros: small size, light
Cons: difficult to focus, so-so image quality

I bought my 40mm pancake lens with a (very) used MX body. I find it a good combination for street photography, as they make a lightweight combination and the 40mm size is just right for the sort of urban shots I like.

I have also used it on my *istDS body since I added the DSLR to my collection, where its 60mm-equivalent field of view puts it into the far end of 'normal'.

That said, I use this lens less and less with time.

For one thing, the focusing ring is quite difficult to use, as it is very thin. I've found myself with my finger on the ring and my thumb on the aperture ring as often as not. Also, the lens is so short that on the *istDS body the focusing ring is actually tucked under the flash cowling, further jamming things up.

My second reason for ignoring this lens is that it seems to drain a bit of the life from my shots. I don't get the colour or contrast I expect, either in film or digital. Sharpness is not an issue, but I've been disappointed with shots from this lens on a few occasions.

Ouch. What can I say, I live in Tokyo.

If you're looking for a small and light street photography combination for digital, get a point-and-shoot. For film, I recommend an old rangefinder. No TTL, it's true, but they're tiny and kinda fun.

edit [2007/03/26]
I sold this lens, as I was no longer using it. I've bumped it down a notch to a '5', as well, because this is nowhere close to the SMC 28mm lens I use as my 'normal', and I only gave that one a '7'. 8)
Veteran Member

Registered: September, 2006
Location: North Idaho
Posts: 665

1 user found this helpful
Lens Review Date: January 9, 2007 I can recommend this lens: No | Price: $100.00 | Rating: 5 

Pros: small, exceptional construction quality
Cons: difficult ot find focus ring when used to 'normal' sized lenses

The SMC Pentax-M f/1:2.8 40mm is the original Pentax "pancake" lens. At the time, it was the only one produced (by Pentax) and was highly desirable for the M bodies. The combination made it the first "pocketable" SLR camera. (But, you needed a large pocket.)

The construction quality is typical of K and M series lenses. All metal and glass. No plastic here! Optically, it was not anywhere as good as the 50/1.4 or 50/1.7 lenses. Probably on par with the 50/2.0 lens. The lens attained 'cult' status and was desirable only because of its size, not because of its optical qualities.

Only rated at 5 because of the fair optical quality. Given a 'no' recommendation because of the price/performance ratio. Today, you should only purchase this lens for the 'collector value', and only if you have a MX or ME body to mate with it. The DA40/2.8 is a much better lens if you want to actually take pictures. This lens still sells for a premium price on the used market, and in my opinion, not worth the cost! It is an "okay" lens, just not worth the premium prices asked and paid.
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