[wallyb]

I'm looking to finalize my lineup a bit and cover the 50mm focal length with some classic primes. I'm considering the following lenses:

Pentax K 50mm f/1.4
Pentax K 55mm f/1.8
Pentax M 50mm f/1.4
Pentax M 50mm f/1.7

I'm looking to get a 1.4 of whichever series, and one of the slower ones. What I'd like to know is -- which series' lenses are better at this focal length? How do the optical formulae compare, as well as the sharpness, bokeh, and all that other stuff? Basically a head to head, K versus M.

Thanks in advance for any replies!

[yeatzee]

I have no experience with those K lenses, but if its any help I wouldn't sell my M 50mm F/1.7 for less than $300!!! (and it cost me $25)

If you want examples let me know.

[Just1MoreDave]

Of those four, one stands out for me: the K55/1.8. It's the same optically as the Takumar on your Rotating list, so if you don't like the Tak for some reason, don't put the K version on your list. In its favor, there's no more advanced version of it, it has a great manual focus sweep of 270º, and it's my first thought for posed portraits. While the M50/1.7 is a nice lens, you can get the same formula in more convenient packages.

There may be small differences between the two f1.4 lenses, but small enough to be ignored IMO. If you get the K55/1.8, the K50/1.4 is a better cosmetic/filter size/cap match.

[wallyb]

Of those four, one stands out for me: the K55/1.8. It's the same optically as the Takumar on your Rotating list, so if you don't like the Tak for some reason, don't put the K version on your list.

I actually love my screwmount 55/1.8 Tak. It's great to know that the K is the same, because I love the pictures I get with the M42 version. I am just looking to get a bayonet version as well.

[Clicker]

[Lowell Goudge]

this is only an observation, but I have always found the M series lenses don't have the same consistancy and feel of K series lenses, mostly the aperture clicks and focusing collar drag just aren't the same,

the impression is that the M series "feel" cheap.

I know it is not scientific but ........

one of the advantages with the M series however, even though I call M series the "mini series" is that most of the lenses use 49mm filters, so you only buy one set and they work on everything. this was done at the expense of speed in the longer lenses.

[bladerunner0427]

I have the Pentax M 50mm 1.4 and it certainly doesn't feel cheap. The focus ring is smooth and well-dampened. The aperture clicks are tight and defined. Nothing loose here.

[stevebrot]

I would take the K 55/1.8 over the M 50/1.7 unless you want the smaller/lighter package. Build is essentially equivalent between the two lenses, but the K 55/1.8 is a small, but definitive step up optically. The K 55/1.8 is harder to find and little more expensive, but worth it.

I would take either of the above two lenses over either of the 50/1.4 models unless you need the shallow DOF and/or 1/2 stop increase in light gathering. If you need f/1.4 either version is probably fine.

Just my preference having recently purchased the K 55/1.8 in preference to the other lenses.

Steve

[lithos]

How do the optical formulae compare, as well as the sharpness, bokeh, and all that other stuff? Basically a head to head, K versus M.

The formulas for the 50s of the same aperture are identical. And I must say, Pentax got the 1.4 (and, by extension, the 1.2) right the first time.

There might be some subtle difference between the Ms and Ks, but I'm not sure if they're that noticeable. I'd go for the M series, if only because they're smaller.

[georgweb]

The formulas for the 50s of the same aperture are identical.

The 50/1.4's according to Dimitrov's are different. He gives three different (although subtle) lens schemes. He does not do this if they are the same.


M42 Super Takumar = S-M-C = K?: http://www.taunusreiter.de/Cameras/Tak50mm1.4_7-lins_1965.jpg


K: http://www.bdimitrov.de/kmp/lenses/primes/_optics/50f1.4-i.jpg



M: http://www.bdimitrov.de/kmp/lenses/primes/_optics/50f1.4-ii.jpg



A, F, FA: http://www.bdimitrov.de/kmp/lenses/primes/_optics/50f1.4-iii.jpg

For some people (incl. me) the use of either K or M lenses on DSLR is clumsier than the M42's. Lots to choose from :-)
Seconding Just1MoreDave's recommendation (he sure must have them all .-) I would get an M42 or K 1.8/55. It's got a special look to the pics.
Georg

[Douglas_of_Sweden]

This might help:

the Normal Lens Shootout Photo Gallery by Sean Carpenter at pbase.com

SMC Pentax Resolution Test Results

As georg shown, while the f1.4 remained a 7:6 solution Pentax tweaked the exact shape of some of the elements several times (believe the Takumar f1.4 was also changed once). The 50/f1.7 and 50/f1.8 (and f2.0) was the same throughout production (6:5's both of them).

The best bang for the buck is probably a M50/1.7 and a K55/1.8 (or 2.0). They render quite different results, cold vs warm, sharp vs portrait-smooth. So it is worth to have both. And both goes for almost nothing. Then you can start wonder if you need a f1.4 or f1.2.

[wallyb]

I just want to pop in and say thanks so much to everyone so far for the quality and very helpful replies.

I'm still in the process of making my decision, though, so any more opinions would be very welcome!

[PentHassyKon]

I was going to link to Sean Carpenter's test but Douglas_of_Sweden beat me to it.

With Sean's 50mm tests - why not go for an f1.2? K or A type: https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/74819-post-you...31-2-only.html

[wallyb]

I was going to link to Sean Carpenter's test but Douglas_of_Sweden beat me to it.

With Sean's 50mm tests - why not go for an f1.2? K or A type: https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/74819-post-you...31-2-only.html

I'm on a bit of a budget to fill this gap in the lineup. I'm looking to spend about $150 max on both lenses. Otherwise, I would!

[PentHassyKon]

Based on what you've already got and if what you're after is differences in rendering then I believe the logical choice would be the M 50/1.7 for the "slow" one.

You've already got the Tak 55/1.8 so getting the K 1.8 may not provide enough of a difference, unless you're trying to collect all the 50'sl

This would then leave the K or M 50/1.4 for the "fast" one. I had an M 50/1.4 before, unfortunately it suffered from a sticky aperture so I rarely used it and ended up getting a Cosina 55/1.2 then an A/1.2 eventually.

K or M? I suspect you'll get the 1st that becomes available that matches what you believe would be a bargain price point - this is how I ended up with my 1.2's