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03-03-2019, 03:34 PM   #1
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Pentax MX/ K-mount lens questions from a film SLR newbie


I have just bought a Pentax MX with a SMC 50mm f/1.7 lens from a used camera shop- my first ever camera! After shooting a couple of rolls I have decided it would suit me better to have a wide angle lens such as a 35mm for the kind of pictures I am going for. I have read some reviews and have heard great things about the FA 31mm limited prime lens. My only concern is that it has auto-focus (which can not be used with my MX) and therefore if I were to buy one I would be paying for this feature that doesn't benefit me at all. Here are my questions for you fellow Pentax owners:

1) Do you think that buying an FA Limited 31mm would be a poor investment as it has auto focus which I can not use?

2) Please could you recommend me great some wide angle (35mm or so) K-mount prime lenses, current or discontinued, that I should consider. I am of the opinion that 'quality is remembered long after the price is forgotten' and therefore feel free to suggest more expensive examples as I wouldn't mind saving up over time! Of course, cheaper examples are also welcome lol.

3) I have read that it is possible to buy adapters to attach lenses designed to fit onto other manufacturer's mounts. If I were to do this on my MX, would this negatively impact the operation of the camera/ lens in any way? Would I need to resort to 'stop down metering' instead of metering normally?

Any help and advice would be greatly appreciated!

Many thanks,


03-03-2019, 03:50 PM   #2
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The FA 31mm is certainly a great lens to use on film / full frame. You might find it a little harder to nail the focus, but given the MX's big viewfinder, I'm sure you'll learn to live with the shorter focus throw in the long term.

I wouldn't worry too much about adapting lenses (other than M42 lenses), because IMO it's more trouble than its worth (with the exception of generic third-party systems such as adaptall).

Lastly, I'd recommend taking a look at the modern Samyang lenses. These deliver really good image quality:

Samyang: Full Frame Third Party Prime Lenses with Aperture Ring |

Of course, there are plenty of gems from Pentax's manual focus lineup as well. Here they are, sorted by user rating:

Full Frame Prime Lenses between 25mm and 40mm |[]=mf&aperturering=1&order=userreviewscore

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03-03-2019, 03:53 PM   #3
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Don't waste your time with adapters other than M42. Most other mounts require an optically corrected adapter that is a short tele-converter. M42 has the same focal flange distance as K mount and the adapter can sit inside the mount. Avoid flanged M42 adapters as they will not allow infinity focus. Stop down metering requires the extra step of stopping down the lens. You can focus with the aperture open but to meter the aperture has to be stopped down.

The other exceptins to the no adapter rule would be the various universal lens mount systems like T-mount or Adaptall...

Last edited by boriscleto; 03-03-2019 at 03:59 PM.
03-03-2019, 04:02 PM   #4
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Of the lenses Adam filtered in his post above I personally recommend the K35/3.5.

They’re less than $125 these days, very sharp, handle colors extremely well and small enough to match your MX.

Alternatively consider the M35/2.8.

They’re a little harder to find and pricier, but they were designed specifically to match the MX-sized camera bodies.

Last edited by monochrome; 03-03-2019 at 04:35 PM.
03-03-2019, 04:20 PM - 1 Like   #5
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Welcome to the forum, the MX is a great camera and handles excellently with primes. The FA31 AF shouldn't get in the way - you may find the focus ring slightly too light to the touch (I drag a 'spare' finger on my FA43 to damp it a bit more), construction is top notch (not always the case with AF lenses) and optically it's great. Of the various manual focus 35mm lenses, the M35/2.8 may suffer from sluggish aperture blades (I had one and have heard of others and it may be common to this specific lens). Another option is the M40/2.8 'pancake', it really is a slim line lens and makes the MX almost pocketable (although it suffers a bit in handling as a result).
03-03-2019, 04:40 PM   #6
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There are tons of interesting options for a MX.

My favorite is the SMC-M 24-35 zoom. Its great for wandering and shooting architecture.

In addition to the K35 f3.5, there are 35mm f2.8 options and 35mm f2.0 as well, the former in manual focus only, the latter in manual or autofocus.

Theres also a 30mm f2.8 that is unusual and well regarded.

Though frankly, the 31mn has the best reputation of the batch.

Id buy one of the less expensive options for now and sell it on once I could afford the 31...

03-03-2019, 10:08 PM   #7
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I'll second the M 40mm F2.8 pancake, especially with your MX. I briefly had a M 35mm F2.8. But I sold it knowing it wasn't going to get much use compared to the 40mm pancake for travel and street photography.
03-04-2019, 01:13 AM   #8
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I have 2 MX bodies. I use M and A lenses for the most part. I recommend an M or A 28mm, F2.8. Nice sharp lens. The 35, 3.5 or 2.8 is nice too. Others have recommended the 40 pancake. And the 50 you already have is terrific. I also have a K 20 F4, for ultra wide.

Can't go wrong with the primes.

03-04-2019, 01:21 AM   #9
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QuoteOriginally posted by monochrome Quote
Of the lenses Adam filtered in his post above I personally recommend the K35/3.5.
QuoteOriginally posted by johnha Quote
Of the various manual focus 35mm lenses, the M35/2.8 may suffer from sluggish aperture blades (I had one and have heard of others and it may be common to this specific lens).
I agree completely with these posts. The K35/3.5 has exceptional image rendering and is often available at a low price. I had a M35/2.8 briefly many years ago when I bought it brand new. It had the sticky or sluggish aperture blades almost immediately. I returned it to the store and was not interested in a replacement at the time. Later acquired the M35/2 new and much later a used K35/3.5 and have had no issues at all with either one.
03-04-2019, 01:25 AM   #10
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I used to quite like the 40mm F2.8 pancake on my MX although it was more due to size than anything else as I didn't find the 40mm focal length all that useful.

IMHO the 31mm limited would be a good choice if you're going to share the lens between a film camera and a DSLR. Otherwise it's quite an expensive option with a lot of capabilty (e.g. AF and the A aperture position) that the MX can't use - although optically of course it'll be great.

If you fancy a play with something cheap then the 37mm F2.8 Mir-1b in M42 is a nice lens, as is the Meyer Optik Lydith 30mm F3.5 - also in M42.
03-04-2019, 04:16 PM   #11
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Thank you all so much for your insights and advice! I much appreciate it. Lots to chew on here... I will do some further research and consider all the lenses mentioned. I really like the idea of the 40mm F2.8 pancake for it's compactness, and the K35/3.5 for it's strong reputation although I might appreciate something slightly faster.
At the moment I'm leaning towards the 31mm Limited as I hear only good things about the build and optics and despite the price, the reassurance of buying it new with a warranty appeals to me.
Thanks again for all the tips!
03-04-2019, 06:29 PM   #12
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I think that some obsess too much about the quality differences between the 28mm and 35mm.
Here is a picture I took nearly 40 years ago with my MX and the original 28/28 lens. I struggle to visualize how the 35/3.5 would improve it.
03-04-2019, 06:38 PM   #13
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I owned two MXs which I used to photograph high school sports for several years. They were my favorite cameras of all time. It took a ton of 5 FPS motordrive shooting to wear one enough to need a repair! My absolute favorite standard lens on the MX was the Pentax SMC-A 35mm F2.0. The one I had was good at F2, very good at F2.8 and exceptional from F4.0 to F11. I sold it after moving to a 28-70 F2.8 zoom. Wish Id kept the 35/F2.0.

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