[clackers]

I have extensively tested most of Pentax K mount 28mm's and APSC and FF and K1, K3 and KP cameras. I would not want to use any of them on a Sony or indeed any mirrorless system. They are all compromised because of the SLR flange distance.

The adaptor compensates for that, Richard!

And yes, adaptors, especially the cheap eBay ones, are one more thing that it is hard to perfectly align, in a sense it's inviting decentreing of the lens.

[pinholecam]

I have the K28/3.5 as well as the M28/3.5
The K is far better for stopped down shooting.
Better off center up to the edges.
The M28/3.5 is noticeably poorer on the edges.

[richard0170]

The adaptor compensates for that, Richard!

Oh no they don't!
Due to the complex lens designs needed for WA lenses on SLRs the image quality can never be as good as those designed for mirrorless systems. There are no optics in most adaptors so no compensation going on at all. Add optics and there will be a further degradation of images. Whether the IQ is still good enough is another matter. However one of the advantages of mirrorless cameras is there ability to be more compact than SLR designs by adding an adaptor to an already large lens, one is negating that advantage.
So, with reduced IQ inherent in the SLR WA lens design and the extra bulk required, why would you choose to use them on a miirorless system? Maybe due to cost I suppose, but many of the best WA SLR lenses are not cheap.

[house]

Oh no they don't!
Due to the complex lens designs needed for WA lenses on SLRs the image quality can never be as good as those designed for mirrorless systems. There are no optics in most adaptors so no compensation going on at all. Add optics and there will be a further degradation of images. Whether the IQ is still good enough is another matter. However one of the advantages of mirrorless cameras is there ability to be more compact than SLR designs by adding an adaptor to an already large lens, one is negating that advantage.
So, with reduced IQ inherent in the SLR WA lens design and the extra bulk required, why would you choose to use them on a miirorless system? Maybe due to cost I suppose, but many of the best WA SLR lenses are not cheap.

You've really been close reading the milc marketing! Its simplified theory though and doesn't directly translate into practical results. Several reviews claim the k3.5/28 is better than the sony fe 2/28 adapted on sony. Not sure I believe that as the k is from the 70s...

[richard0170]

You've really been close reading the milc marketing! Its simplified theory though and doesn't directly translate into practical results. Several reviews claim the k3.5/28 is better than the sony fe 2/28 adapted on sony. Not sure I believe that as the k is from the 70s...

Nothing to do with reading any marketing. I know. from experience my WA range finder lenses are better than my SLR ones (apart from the lack of close focusing). My K 28mm f3.5 is very good on my K1, but it comes at a cost of being relatively large and heavy with a slow maximum aperture. Of course in real world use it is more than acceptable, but once one has seen or used something better one tends to be more picky. If money were no object I would choose one of Voigtlander's 28mm f2 lenses, which are fast, compact and in IQ terms wonderful.

I know if I had a Sony A series camera and budget was important I would be looking at their offerings or those from Tamron, Sigma, Kipon or Samyang before adapting any WA to the system. I would be very surprised if a modern mirrorless lens performed worse than its ancient SLR counterpart. I would be very sceptical of reviews which suggested otherwise. The only reason for this to happen that I can think of is shoddy production values in the modern age.

[tonynon]

I have both. The M 35mm f2.8 is surprisingly good, especially when stopped down to f5.6 to 11. I have had two copies of the M 40mm f2.8 (I really like the lens!). My current copy is better than my first, so there appears to be some sample variation based on my experience alone. Both render colours in the Pentax way, If you shoot a lot of B&W you may notice the 40mm produces nicer contrast, being a 4 element Tessar design. Personally I prefer the 40mm as I prefer the focal length over 35mm for FF. However some find the small size fiddly for handling (I don't) and are put off by the lens for that reason. The M 35mm is not much larger but few seem to complain about its handling. Both are reasonably priced, so I would be inclined to get both and keep the one you prefer best.

Thanks for this very useful review and recommendation! I figure it might be interesting to make an update on this thread. Since my original post, I moved the Pentax-M 28mm f/3.5 on to a very happy buyer online. Fate also had it that I collected a few lenses in the meantime. I found a Pentax-M 35 f/2.8 for 50 at a local camera shop, a Pentax-K 35mm f/3.5 for 60 shipped, and finally bit the bullet on a Pentax-M 40mm f/2.8. Ack, too many lenses for what I shoot. The M 35mm f/2.8 one rigorous aperture blade cleaning later is a labrador. However, I'm moving it on because, word has it the K 3.5 is a much better lens, and, well, I have some point and shoots with decent 35 2.8's anyway. I haven't played around with the 40mm too much yet, however, I think I will take your recommendation and load my ME SE up with some HP5 and the 40mm. Ah how I love diagonal screen focusing!

---------- Post added 02-28-22 at 11:38 AM ----------

You've really been close reading the milc marketing! Its simplified theory though and doesn't directly translate into practical results. Several reviews claim the k3.5/28 is better than the sony fe 2/28 adapted on sony. Not sure I believe that as the k is from the 70s...

Phillip Reeve has a very interesting review of the Pentax-K 28mm.

Review: Pentax K SMC 28mm 1:3.5 - phillipreeve.net

It seems as a landscape lens, the Pentax wins due to great sun stars, and lack of the absurd distortion of the Sony FE 28mm f/2 is plagued with

[clackers]

Oh no they don't!
Due to the complex lens designs needed for WA lenses on SLRs the image quality can never be as good as those designed for mirrorless systems. There are no optics in most adaptors so no compensation going on at all. Add optics and there will be a further degradation of images.

Richard, I'm quoting you. You said flange distance.

The adaptor makes up the difference in the flange distance, there is absolutely no problem in using a DSLR lens on a mirrorless.

I shoot both Pentax and Sony, so I know!

So, with reduced IQ inherent in the SLR WA lens design and the extra bulk required, why would you choose to use them on a miirorless system? Maybe due to cost I suppose, but many of the best WA SLR lenses are not cheap.

On the issue of mirrorless lens designs - that was not the topic, Richard, the topic was DSLR lens designs - they have advantages and disadvantages because of their short flange distance.

In theory you can do without the retrofocal group, but in practice, you put it in anyway. You want the rays to come back gun barrel straight. A high quality MILC lens looks very much like a high quality DSLR lens, and weighs and costs as much.

And wide angles so close to the sensor are problematic.

The bent light from the edges is extreme. Enough to trigger a grain of film, but perhaps not a digital sensor. That's why makers like Leica and Sony at times have had to add a distracting, image affecting microlens array in front of the sensor to try and capture more of the light and lessen the vignetting. This in turn leads to artefacts like purple colouring. Pinholecam actually paid to have his microlens array taken off his Sony A7.

[whojammyflip]

I've compared the M 28 2.8 v1 to the M 28 3.5, using MTF Mapper and a proper test target, mounted on a board etc. The M 28 3.5 was sharper until f8. The 28 2.8 will match it at f8. I think you would only notice the differences in real life, if doing side by side comparisons, any lens on the day would be fine.

Take a look at MTF Mapper for quantifying this stuff:

MTF mapper download | SourceForge.net

[Caspert79]

For whoever is interested: I tested the SMC Pentax 28mm f/3.5 against the Mamiya E 28mm f/2.8. The link is here:
Mamiya Sekor E 28/2.8 vs SMC Pentax 28/3.5

I think this is an excellent lens, even on a 42+ mp sensor. I don’t share the view mentioned in this thread about this lens having significant field curvature. In fact, corners are already sharp at f/3.5 when centrally focused at a subject at infinity. Contrast, colors, flare resistance, build quality are all excellent.

[kypfer]

If you shoot a lot of B&W you may notice the 40mm produces nicer contrast, being a 4 element Tessar design

According to the review here SMC Pentax-M 40mm F2.8 Reviews - M Prime Lenses - Pentax Lens Reviews & Lens Database and Pentax's own "Lenses and Accessories" publication, the Pentax-M 40mm f/2.8 is a five-element/four-group lens … was there another version?

[northcoastgreg]

I was wondering if owning the Pentax K 28mm f/3.5 would make it redundant to own the Pentax-M 28mm f/3.5 as well? Would it be a good choice to replace the M 3.5 with the later version of the M 2.8?

I would contend that ownership of the K 28 f3.5 would make ownership of the M 28 3.5 redundant. There may not be much difference between the lenses in resolution (pretty much true for all the vintage Pentax 28mm lenses), but in terms of color rendering, contrast, rendering of detail, and overall aesthetic qualities, the K 28/3.5 is the best of the f2.8 and f3.5 Pentax 28s. Nor would I believe it would be a good choice to replace an M 28/3.5 with the version 2 of the M 28/2.8. The claim to fame of the M 28/3.5 is better contrast than the f2.8 versions. Again, with these lenses, you have to avoid getting caught up in differences of resolution, which may exist but are too slight to be of any real practical significance. But the contrast and color rendering differences are noticeable, and that's what has largely determined which lenses are preferred by a majority of users.

Image shot with the K 28/3.5:

[richard0170]

According to the review here SMC Pentax-M 40mm F2.8 Reviews - M Prime Lenses - Pentax Lens Reviews & Lens Database and Pentax's own "Lenses and Accessories" publication, the Pentax-M 40mm f/2.8 is a five-element/four-group lens … was there another version?

My mistake. I always assumed it was a Tessar design due to its size. Thank you for correcting me. One lives and learns.

I have had two copies of this lens. The first was decent on film but unremarkable and distinctly average on digital. My current one is much better and displays more contrast than the first, even on digital. Clearly this has nothing to do with it being a Tessar design!

[travelswsage]

Nice shot northcoastgreg!

I only have the k 28 f3.5 so cant offer any comparisons but can add that if you are interested in infrared or might be in the future the k 28/3.5 is an excellent choice with very little hotspotting.

[cyberjunkie]

I own/owned three manual 28mm Pentax lenses.
1) 3.5/28mm M. Used only on film long long time ago. I didn't notice any particular problem, apart from speed, which was a more relevant aspect at the time, with relatively slow emulsions. Now it should perform almost as good as the previous K version. Unless you find it for really cheap, I would go for the K (optically and mechanically it's a touch better from what I read).
I exchanged it in the first half of the eighties for the following one (adding a good amount of money, but still much less than today's value).
2) 2/28mm K ("Pentax Distagon" aka "Hollywood"). Floating design, very good, especially for close range use.
Because of the value I never used it very much, especially on the K-1, which is a real pity. I promised myself I would start to routinely use my most valuable lenses, but so far I'm still missing the resolve to bring them with me on long travel photography trips.
3) 3.5/28mm K. I got it for cheap because of some fungus problems. Opened and cleaned it myself.
On the K-1 it's one of the best landscape/nature lenses. Modern sensors make up for the relative lack of speed, and overall performance at infinity (or close to it) is really good, especially considering the price.
Stopped down a little it rivals much more modern lenses (a lot more expensive and bulkier).

Price/performance wise, the number 3 is the one I would choose, among those mentioned in the title of the thread.
There are a few other PK manual lenses I would recommended, though.
For handheld low light and night photography I love the Samyang 1.4/35mm (though it's not as wide as the other mentioned), and had more than decent results with the Soligor/Tokina 2/28mm (mine is M42 though, and I don't know if it was ever made in PK mount). A second generation Kiron 2/28mm (PKA) is also very good. Not the same as the Kiron/Vivitar with same specs, the former is better.
The SMC 2.8/30mm is also good, if you can find one...
Btw, most of the early K line is well worth checking, in my opinion. A few of the most extreme focals show their age, but most of them are still more than fine even on high-res sensors. The mechanical quality is great (as good as the SMC Takumars!). In fact, most of them are still in great shape, and offer a very precise, well dampened feeling when focusing.

[richard0170]

Btw, most of the early K line is well worth checking, in my opinion. A few of the most extreme focals show their age, but most of them are still more than fine even on high-res sensors. The mechanical quality is great (as good as the SMC Takumars!). In fact, most of them are still in great shape, and offer a very precise, well dampened feeling when focusing.

Indeed. My particular favourite is the K 35mm f3.5. It doubles up as a really nice compact standard on my KP.