[lytrytyr]

for one major criteria (resolution) see the following where almost all M and K's, in the 18-135 mm range, are tested.
Yoshihiko's PHOTO site

The results of that site need to be interpreted with caution,
since they are based on visual perceptions that high contrast is a proxy for resolution.

For example, the site overestimates the edge resolution of the contrasty FA*24/2,
and underestimates the sharpness of the less contrasty M100/2.8.

[dms]

I agree, but (1) I think the FA 24mm lens is a notorious example! And (2) by in large the comparison of older K vs M lenses is meaningful.

Older lens test, which used a target, film, and visual interpretation of lines per mm, have the same problem. Yoshihiko in discussing lenses has said a resolution test is only part of the story (and you are saying even this is not a true measure).

But as regards the M vs A lens question--the tables should provide a sense of what is usually the case--and are backed up/consistent generally with anecdotal information--as in Stan's Pentax site.

In the end it is also how the lens physically feels, is the size right, rendering qualities that are not measured... Nothing replaces using the lens.

[robbiec]

The Ks are old school over engineered works of art, the Ms are engineered to a price and size. Take a K50 f/1.4 and compare it to a M50 f/1.4, all things being equal the M may have a slight optic advantage due to coating improvements but it feels rough compared to the K. Tactile wise the Ks will always and I mean always stomp all over an M. Could be the weight difference and size having an effect but even the rubber on the focus ring feels cheaper on an M compared to a K

[stevebrot]

I have only a very limited sample to draw from, but both lenses were aimed at the same market segment and should be a good basis for comparison:

• Pentax-K 55/1.8
• Pentax-M 50/1.7

Both have very similar construction, though the K 55 is obviously larger in diameter and has a beefier feel. The K 55/1.8 traces its lineage to the Super-Takumar of the same focal length/max aperture. The M 50/1.7 was a new design. In actual use, the M 50/1.7 is quicker to focus than the K 55/1.8 (less dampened?). It is also much nicer to have mounted to the compact cameras for which it was designed. Excellent balance. I have been using mine for since the early 1980s mounted to a Ricoh XR7. The M lens also is quite at home on my Pentax KX and Ricoh XR-2s (almost identical dimensions), but the K lens feels sort of clumsy on the XR7 and my Pentax Super Program (duh!).

As for build, I would consider both to be equivalent and among the best available at the time. This may not be the case for other focal lengths.

Optically, the edge goes to the K 55/1.8. Both lenses are sharp and resistant to flare, but the K 55/1.8 has the edge (slightly) for resolution and contrast. I should note, however, that the K 55/1.8 is my best fast 50...and I have a lot of them.

Avoid the M-series lenses as a matter of course? No way! Most are great lenses. Are they inferior to the K-series? It all depends how you define inferior. Are they better than equivalent "A" series? Now there is an entirely different rant


Steve

(...loves the K-series lenses, but would generally not pay a premium price for one...with a few exceptions!)

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Last edited by stevebrot; 02-19-2012 at 08:01 PM.

[Lowell Goudge]

The Ks are old school over engineered works of art, the Ms are engineered to a price and size. Take a K50 f/1.4 and compare it to a M50 f/1.4, all things being equal the M may have a slight optic advantage due to coating improvements but it feels rough compared to the K. Tactile wise the Ks will always and I mean always stomp all over an M. Could be the weight difference and size having an effect but even the rubber on the focus ring feels cheaper on an M compared to a K

Your description of the feel is spot on, rough was the word i was looking for. I tried once a M100/2.8 against a K105/2.8 and while the m lens might be sharper ( almost anything is wide open compared to the K105> the tactile feel of the M just isn't the

[monochrome]

I have only a very limited sample to draw from, but both lenses were aimed at the same market segment and should be a good basis for comparison:

• Pentax-K 55/1.8
• Pentax-M 50/1.7

Both have very similar construction, though the K 55 is obviously larger in diameter and has a beefier feel. The K 55/1.8 traces its lineage to the Super-Takumar of the same focal length/max aperture. The M 50/1.7 was a new design. In actual use, the M 50/1.7 is quicker to focus than the K 55/1.8 (less dampened?). It is also much nicer to have mounted to the compact cameras for which it was designed. Excellent balance. I have been using mine for since the early 1980s mounted to a Ricoh XR7. The M lens also is quite at home on my Pentax KX and Ricoh XR-2s (almost identical dimensions), but the K lens feels sort of clumsy on the XR7 and my Pentax Super Program (duh!).

As for build, I would consider both to be equivalent and among the best available at the time. This may not be the case for other focal lengths.

Optically, the edge goes to the K 55/1.8. Both lenses are sharp and resistant to flare, but the K 55/1.8 has the edge (slightly) for resolution and contrast. I should note, however, that the K 55/1.8 is my best fast 50...and I have a lot of them.

Avoid the M-series lenses as a matter of course? No way! Most are great lenses. Are they inferior to the K-series? It all depends how you define inferior. Are they better than equivalent "A" series? Now there is an entirely different rant


Steve

(...loves the K-series lenses, but would generally not pay a premium price for one...with a few exceptions!)

Subjectively, K lenses on K cameras feel better then M lenses on K cameras, and vice versa. If only there were Pentax L lenses.

[John Poirier]

I have a fairly good selection of lenses from both series, mainly because I did much of my lens buying when they were far cheaper so I could indulge my curiosity. I prefer the K lenses in general because their larger size works better for me.

While smaller, the M lenses are very sturdy. The lenses I have owned longest and used most are M series- a 50/1.4, 28/2.8 and 135/3.5, bought new in the early 1980s. The paint is well worn but they function perfectly despite much service in extremely bad conditions. Nothing wrong with that build quality.

Optically, there are variations between the two series but nothing that I would say gives one a definitive. edge. There may be some diffenences in colour rendition, but those are insignificant these days given the ease of colour correction.

What it boils downn to is that either series is fine, so go for availability and affordability.

John

[lytrytyr]

All generalizations are false!

We keep talking about the "K series" as if it was a coherent group of lenses like the Ms, Fs, or FAs.
But in reality, the unofficial term covers a variety of lenses.

There are solid old Takumars rebodied from screw to bayonet mount like the 55/1.8,
and then there are the lenses that were listed together with the Ms,
at focal lengths of 15, 18, 24, 28, 30, 50/1.2, 135/2.5, 200/2.5, 300/4, and longer,
as well as specialized lenses like the 28/3.5 shift or bellows 100/4.

[monochrome]

All generalizations are false!

We keep talking about the "K series" as if it was a coherent group of lenses like the Ms, Fs, or FAs.
But in reality, the unofficial term covers a variety of lenses.

There are solid old Takumars rebodied from screw to bayonet mount like the 55/1.8,
and then there are the lenses that were listed together with the Ms,
at focal lengths of 15, 18, 24, 28, 30, 50/1.2, 135/2.5, 200/2.5, 300/4, and longer,
as well as specialized lenses like the 28/3.5 shift or bellows 100/4.

Is there a distinction between SMC PENTAX and smc PENTAX?

[Lowell Goudge]

All generalizations are false!

We keep talking about the "K series" as if it was a coherent group of lenses like the Ms, Fs, or FAs.
But in reality, the unofficial term covers a variety of lenses.

There are solid old Takumars rebodied from screw to bayonet mount like the 55/1.8,
and then there are the lenses that were listed together with the Ms,
at focal lengths of 15, 18, 24, 28, 30, 50/1.2, 135/2.5, 200/2.5, 300/4, and longer,
as well as specialized lenses like the 28/3.5 shift or bellows 100/4.

Although there are generalizations please note that most of the lenses in your list were never released as M lenses. The K300/4 is quite different than the M300/4 for example and there el ever was an M50/1.2 28/2 with fixed rear element, or M135/2.5 of 200/2.5. These were all K lenses. Not remounted takimars or anything else

[vrrattko]

Although there are generalizations please note that most of the lenses in your list were never released as M lenses. The K300/4 is quite different than the M300/4 for example and there el ever was an M50/1.2 28/2 with fixed rear element, or M135/2.5 of 200/2.5. These were all K lenses. Not remounted takimars or anything else

I think what Lytryr was trying to pointing out was that some K lenses spread over longer period were still produced alongside the M series. That is true for few of them: K28 shift, K85 soft, K135/2.5, K50/1.2, K24/2.8 and perhaps some more. I don't know if there's any M series lens which shares the optical formula with its K equivalent, though.

[baro-nite]

I don't know if there's any M series lens which shares the optical formula with its K equivalent, though.

50/4 macro
100/4 macro
2000 reflex

apparently the 50/1.4 is not identical, but I gather the differences are minor

[lytrytyr]

I think what Lytryr was trying to pointing out was that some K lenses spread over longer period were still produced alongside the M series. That is true for few of them: K28 shift, K85 soft, K135/2.5, K50/1.2, K24/2.8 and perhaps some more.

The list I gave was comprehensive, taken from a Pentax brochure dating back to the early 'eighties.

[dms]

There are Super Multi Coated and then smc--in the m42 series. The latter have, as I recall, rubber rather than metal for covering of focus ring. All mine are the former. As I recall there are no other significant generic differences.