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02-07-2010, 03:05 AM   #1
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Looking for a Lens. Cannot determine if it is compatible with K-x

I have a Pentax K-x and Ive been looking at faster prime lenses. I would like a 1.8 or a 1.4 and cannot figure out if certain lenses actually work with my camera. I would like to take pictures of my martial arts so I could capture fast pace movements. I found this lens
Pentax C25011KP 50mm F 1.4 Manual Lens
Amazon.com: Pentax C25011KP 50mm F 1.4 Manual Lens: Camera & Photo here is a link so you know the specs. Can anyone tell me if this is a decent lens. if it is compatible with a k-x and if not tell me how to determine what will work on my camera?

This is what I have found on my own searches
"Lens mount. On its front panel the Pentax Kx features a stainless steel Pentax KAF2 bayonet mount which allows use of KA, KAF, KAF2, or KAF3 lenses. The K-x can also accept K-mount, 35mm screwmount, and 645 / 67 medium format lenses with an adapter and some usage restrictions. The Kx is compatible with Pentax's Supersonic Drive Motor (SDM) lenses, but doesn't support power zoom functionality on lenses with this feature. "

Problem is some dont have listed mounts and this one in particular is labeled Mount : C which leads me to believe it would not fit

thanks a lot in advance

02-07-2010, 03:21 AM   #2
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This is a C mount lens meant for security cameras (may also work with old 8 and 16 mm film movie cameras). Will not work with the Pentax K mount. If you want an f1.4 50mm lens, seek out a Pentax A50 f1.4 (going rate about $200 or more right now). If you want full auto but don't want to spring for the DA*55 f1.4, the FA50 f1.4 is a good option but again, expensive ($250-$400 depending on condition and who you buy it from).

My personal recommendation would be the Pentax A 50mm f1.7. Ounce for ounce, one of the best manual focus lenses Pentax ever made (In my opinion).

You could also go for the screw mount Super Takumar options (50 f1.4, 55 f1.8, etc) but those require an adapter to use.

Keep in mind that 50mm range on an aps-c sensor is a bit of a specialized lens. You might be better off as a general purpose (still expensive) Normal lens, with one of the 30ish mm range lenses. Ebay, Pentax Forums marketplace, are good places to look. Since I'm talking about expensive lenses anyway, in the faster range, the Pentax FA43mm f1.9 Limited is a tough act to follow. A little slower but very nice still is the DA40mm f2.8.
02-07-2010, 03:34 AM   #3
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What about this Lens?
Pentax Lens Review and Specification Database - 50mm F1.4
It seems very good. Do I need an adapter for this one? I dont think so since it is a K mount. It seems like its pretty cheap and I already found one on ebay for about $145
02-07-2010, 04:04 AM   #4
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QuoteOriginally posted by CrossStealth Quote
What about this Lens?
Pentax Lens Review and Specification Database - 50mm F1.4
It seems very good. Do I need an adapter for this one? I dont think so since it is a K mount. It seems like its pretty cheap and I already found one on ebay for about $145
You can use this lens on your camera without problem. And it won't allow you to use all auto exposure modes.

02-07-2010, 04:11 AM   #5
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QuoteOriginally posted by CrossStealth Quote
What about this Lens?
Pentax Lens Review and Specification Database - 50mm F1.4
It seems very good. Do I need an adapter for this one? I dont think so since it is a K mount. It seems like its pretty cheap and I already found one on ebay for about $145
No adapter needed, it's a K lens, predecessor to the M lens which is the predecessor to the A lens. Be aware that it's a Full manual lens. Check your manual for what it says on using K and M lenses. It will require that you understand a few things about exposure to use a lens such as this. An A lens will give you full auto exposure capability while still being manual focus. Keep in mind that the prices shown in those reviews appear to be a couple years old and have jumped drastically since then.

A50 f1.4

A50 f1.7

In both cases (even with the M and K versions) you can do much worse. The K lenses though seem to be becoming somewhat of a cult collector classic. With good reason, mind you, they are stunning IMO but be prepared to pay good money for them.
02-07-2010, 04:17 AM   #6
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Ok 1 more question. Is Asahi SMC Pentax-M 50mm f1.4 Takumar K-Mount Lens the same one as listed above? Or is it some other side brand with worse quality? I think its the same but its always good to double check with you experts
02-07-2010, 04:49 AM   #7
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QuoteOriginally posted by CrossStealth Quote
Ok 1 more question. Is Asahi SMC Pentax-M 50mm f1.4 Takumar K-Mount Lens the same one as listed above? Or is it some other side brand with worse quality? I think its the same but its always good to double check with you experts
The Pentax-M 50 is the update to the K version (from what I understand) optically probably very similar. I've never seen a takumar K mount 50mm lens (doesn't mean they don't exist). The only ones I've ever seen are M42 Screw mount lenses. These will work with your camera but require an adapter (M42-K) and it's recommended that you get one made BY Pentax for best use. Both lenses will give you very good results.

One thing I think it worth noting is that these lenses were made in the days when Slides were very popular. Keeping in mind that slides are meant to be projected onto a 50+ inch screen, the lenses needed to be very sharp. Add to that you are using only (effectively) the center part of the glass and you really cannot go wrong with any of them. The only real factor becomes, what you you willing to do in the everyday use? In other words, how much auto capability are you willing to live without?
02-07-2010, 04:55 AM   #8
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To answer your question. I would prefer to do everything manually so I can have a better understanding and better control over every shot. I am a beginner to cameras but I am usually a fast learner

Oh so what is the exact model I should search to get the else that will not need adapters or anything?
Is it the SMC Pentax-A 50mm F1.4 or SMC Pentax-A 50mm F1.7


Last edited by CrossStealth; 02-07-2010 at 05:03 AM.
02-07-2010, 12:12 PM   #9
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QuoteOriginally posted by CrossStealth Quote
Oh so what is the exact model I should search to get the else that will not need adapters or anything?
Adapters are not to be feared, and will open up many possibilities for you. An official Pentax M42-PK (screwmount to bayonet) adapter lets you safely use a huge range of cheap but great (or sometimes not so great) lenses. All will be manual focus; many will allow auto aperture control as well as manual. I'd say, don't get hung up on a specific lens, but it's hard to go wrong with almost any Pentax product. Take a look a the the lens review sections here for details.
02-07-2010, 03:15 PM   #10
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QuoteOriginally posted by CrossStealth Quote
Oh so what is the exact model I should search to get the else that will not need adapters or anything?
Anything that says Pentax SMC, Pentax M, A, F, FA, DA, D-FA in the name. The only lenses that require adapters are the ones that are described as screwmount or M42 lens. And as far as I know (although I suspect someone will know of a counterexample), that included *no* lenses labeled "Pentax" - just most of the ones labeled "Takumar".
02-07-2010, 06:05 PM   #11
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Great! that helps a lot now Im just looking for the best one I can afford. I want a 50mm f1.4. out of those series are any of them better then others? or is A the same as AF etc
02-08-2010, 05:07 AM   #12
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Now that you have narowed down your choices visit the lens review databases to see what people think of each of your shortlisted items...
02-08-2010, 12:13 PM   #13
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QuoteOriginally posted by CrossStealth Quote
Great! that helps a lot now Im just looking for the best one I can afford. I want a 50mm f1.4. out of those series are any of them better then others? or is A the same as AF etc
Well, you need to know what those abbreviations mean, so you realize which have autofocus, which have autoexposure, etc. I believe you've already been pointed to info on that, but basically, anything with "A" or "F" in the name has autoexposure; anything with "F" or "D" has autofocus.

I think you'll quickly discover as you read reviews and price these things that if you're looking to save money, getting an 50/1.7 makes a lot more sense than a 50/1.4 - just as good optically, practically as fast, and a lot cheaper. but if you're looking to buy a brand new lens with autofocus, then the FA50/1.4 is the only option.
02-08-2010, 12:31 PM   #14
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I agree with Mark. Saw a Pentax SMC-A 50mm F1.7 in the marketplace this morning for a reasonable price. This lens will give you auto aperture for getting your feet wet, so that when you don't have the time to go at a slower pace it can expose the photos correctly for you, but also has an aperture ring when you want to take the time and experiment with it. It will probably also be about half the price of a Pentax SMC-A 50mm F1.4 lens as well. From what I have read about the two lenses, the F1.7 is just as sharp or sharper than the F1.4 lens is at F1.7 (the F1.4 is somewhat soft wide open). Also, the 1/2 stop between F1.4 and F1.7 is almost moot when you can shoot with such high ISO on the K-x, and both lenses give nice out-of-focus rendering at the small apertures.

So, 2nd vote for a Pentax SMC-A 50mm F1.7, Good luck with your choice.
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