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01-08-2012, 06:12 AM   #1
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How to differentiate between SMC (K) and M lenses


I have been offered a 135 mm f3.5 SMC(k) lens for a song. It seems a niceish lens for the price.

It seems that the SMC's are slightly better rated than the M versions.

My question is -- How does one tell the difference (generally) between an older SMC(K) lens and the later M versions? The photos on this site appear identical. (But i can not see the front ring in the photos)

Best regards


Last edited by bmf; 01-08-2012 at 06:18 AM.
01-08-2012, 06:52 AM   #2
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The most reliable way to tell the difference is by reading the info off the front of the lens. In this case you can't, and the two versions do look very similar. Note that the K version has a longer focusing ring, or at least has more rows of knobs on the grip. (The K version is significantly longer and heavier than the M.) The two versions do have different optical formulae.
01-08-2012, 07:21 AM   #3
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On M lenses, it said M on the ring.
K lens would not say anything

Last edited by MegaPower; 03-11-2013 at 11:21 PM.
01-08-2012, 07:27 AM   #4
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M series lenses should almost always read "SMC Pentax-M" on the front filter ring. The K version will just say SMC Pentax. K lenses are also generally longer and bulkier, and the M series primes were more consistent with using a 49mm filter thread for everything shorter than the 200mm f/4. The K series tended to use 52mm filter threads for primes but the short and long lenses transition to using larger filter threads sooner than with the M series. For specific focal lengths there are often other clues like the aperture markings or the number of ribs on the focus ring.

01-08-2012, 07:30 AM   #5
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No one has said it so here goes: When possible refer to the Lens Review section here and to Bojidar Dimitrov's Pentax K-Mount Page.

Welcome to Bojidar Dimitrov's Pentax K-Mount Page

There are diagrams, descriptions, and photos of the lenses to use for comparison.
01-08-2012, 11:23 AM   #6
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All the other lenses have letters indicating their series, but the first series doesn't. We call them Ks but the name is really SMC Pentax. Usage and function are the same as the M series lenses, but M series lenses almost all have a different optical design.

If the photo just shows the side, identification is sometimes hard. With the 135/3.5, the K version is much larger, with no pull-out hood. The K also has a square baffle around the rear element inside the mount, common on K telephotos but not on M series. The K only has 6 aperture blades.

If you were looking at 50/1.4 lenses, the differences are really small.
01-08-2012, 12:03 PM   #7
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M lens has a hood, the K doesn't.
01-09-2012, 05:22 AM   #8
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Original Poster
Thanks all!



01-17-2012, 05:30 AM   #9
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There are a lot of replies that a specific here, which lead to confusion. For example M series have hoods, K series don't. My K 300/4 has a hood, so scratch that one.

K have 6 aperture blades. Not always....

The only way to tell is the front besel K series lenses are called that because they were introduced with the k series cameras, but all lenses say in the name is SMC Pentax... M series lenses came out with the m series cameras, are generally smaller lighter than thie same focal length k series lenses, and have less fast options. Gone are the 50/1.2 and 135/2.5 and 200/5 for example. Many K lenses use 52mm filters where as M lenses where optically possible use 49mm

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