[camerasup]

I discovered I own the K version in excellent condition. I mistaken my lens as an M because they look the same. Where can I find more information on how the Pentax M 1.4 was improved upon.... I assume they are the same.

[gofour3]

I discovered I own the K version in excellent condition. I mistaken my lens as an M because they look the same. Where can I find more information on how the Pentax M 1.4 was improved upon.... I assume they are the same.

This is your best bet:

Pentax Lenses - Pentax Lens Reviews & Lens Database

Pentax Normal Prime Lenses

Phil.

[Adam]

I discovered I own the K version in excellent condition. I mistaken my lens as an M because they look the same. Where can I find more information on how the Pentax M 1.4 was improved upon.... I assume they are the same.

The M version is physically smaller.

[dms]

If you read here [http://stans-photography.info/] about "best normal lens" (or words to this effect) you will find discussion--it appears from same that the K/M 50mm f/1.4 are optically the same same and very minor "tweaking" occurred w/ the A (50mm f/1.4). Note the site toggles between detailed discussion and summary version.

However, from what Adam wrote/Phil's link to K mount lens tables--and the general trend to smaller diameter lens housing--the M is possibly less robust/more likely to suffer damage from side blows--anyway that was the trend w/ Nikons when they also downsized lenses.

[kiwi_jono]

This is worth a read too: Brief Comments

The K and M are supposed to be the same optical design where as there was a small change going to the A / F / FA versions. My tests of a M against an A tends to indicate that the "A" version does have a slight advantage in sharpness near wide open.

[camerasup]

Thanks everyone for your replies. Good info.

[lytrytyr]

The K and M are supposed to be the same optical design where as there was a small change going to the A / F / FA versions. My tests of a M against an A tends to indicate that the "A" version does have a slight advantage in sharpness near wide open.

The M has a flatter cemented join than the K and A versions,
which is supposed to favor sharpness at a distance.

Among the Pentax 50/1.4 lenses, I only have the M,
and it is certainly extremely sharp at infinity.

[glasbak]

The K and M are supposed to be the same optical design.

The K is probably the same optical design as the latest takumar 50/1.4, (it is also radioactive and suffers from yellowing), The M is not radioactive.
The M optical design is very similar (as are all double gauss 50/1.4 designs) but not the same.
The M mechanics are inferior to the K (and takumar).

[macTak]

The M has a flatter cemented join than the K and A versions,
which is supposed to favor sharpness at a distance.

Maybe that is why I always preferred the K to the M (having had both), as I generally used it for closer work. From my experience of using both, the difference in optical construction (minor though it may look) is definitely noticeable in the "look" these two lenses have (never tested them side by side for sharpness, but both were of course excellent); I much preferred the rendering of the K, which seemed to have more of that infamous and elusive 3D effect and generally better bokeh too. And I never had any complaints about the sharpness of the K.

[lytrytyr]

The M mechanics are inferior to the K (and takumar).

Unlike the "M", the so-called "K" lenses are not a uniform series.

For example, the K 24/2.8 is an "M" lens in all but name
(probably because it has a 52mm filter thread instead of 49mm.)

And I have certainly noticed no mechanical weakness
after using "M" lenses (20/4, 50/1.4, 100/2.8) intensively for thirty years,
in all sorts of environments.

OTOH, my 55/1.8 Tak has developed a little slop in the focusing helicoid.
Nothing major, but it's there.

[Cabessius]

I have both, and I consider them real gems.

Side by side:



2 pics from this afternoon, RAW pp´ed in Silkypix. Only touched the exposure, set to auto (-0,14 for M and + 0,06 for K).
Both at f8, 1/800s, ISO 400.

M 50mm


K50mm

[glasbak]

Unlike the "M", the so-called "K" lenses are not a uniform series.

For example, the K 24/2.8 is an "M" lens in all but name
(probably because it has a 52mm filter thread instead of 49mm.)


OTOH, my 55/1.8 Tak has developed a little slop in the focusing helicoid.
Nothing major, but it's there.

The K 50/1.4 (and takumar) uses brass in its focus heliocoid construction, the M aluminum, that brass helps maintaining the buttery focus feeling after all those years.
The M version relies more on the grease to prevent the not very smooth aluminum on aluminum movement.
Most initial K mount lenses have these superior, and more expensive construction, the K 24/2.8 came later.
In general the early K lenses and very first M lenses have a better finish, the newer the M lens, the cheaper the finish.

Slop in the takumar can probably solved, depends on what the cause is.

[camerasup]

Maybe that is why I always preferred the K to the M (having had both), as I generally used it for closer work. From my experience of using both, the difference in optical construction (minor though it may look) is definitely noticeable in the "look" these two lenses have (never tested them side by side for sharpness, but both were of course excellent); I much preferred the rendering of the K, which seemed to have more of that infamous and elusive 3D effect and generally better bokeh too. And I never had any complaints about the sharpness of the K.

I noticed that 3d effect and somebody pointed it out when I showed them a picture. I'm getting a bit better at focusing with the lens now. I wish to use a digital FF just to be able to use this lens at a wider angle. Please Pentax, make us a few FF just one time.

[boriscleto]

The K is probably the same optical design as the latest takumar 50/1.4, (it is also radioactive and suffers from yellowing), The M is not radioactive.
The M optical design is very similar (as are all double gauss 50/1.4 designs) but not the same.
The M mechanics are inferior to the K (and takumar).

The K is not Thoriated. Pentax switched to Lanthanum in 1975 with the K series.

[monochrome]

The K is probably the same optical design as the latest takumar 50/1.4, (it is also radioactive and suffers from yellowing),

Your suspicion is likely incorrect.

List of Thoriated lenses known and rumored to exist.

The K is not Thoriated. Pentax switched to Lanthanum in 1975 with the K series.

Agreed.