K mount 50mm prime lens

<p>Im looking at buying a prime lens for my old film pentax that uses the k mount (Ka) and my choice is either the Pentax smc 50mm 1.7 or the 2, is it worth the extra cash for the 1.7? </p>

 

<p>It is a matter of economics. If you are content with a f2, the m lenses are pretty cheap, and the a lenses are very reasonable. This is where you would spend the least. Dropping to the 1.7 gives you more low-light options. You just have to decide what your main use for the lense will be. If you are looking on ebay, you can probably buy a camera and lens for what it would cost for just the lens. If you have any future digital plans, the "A" lens will let you use you use the camera settings while in mnual focus as opposed to being forced to the manual setting of the camera.<br>

There is a bit of a price difference between "A" and non "A" lenses. 50mm were very common, so the prices tend to be less than alot of other primes.</p>

<p>It is only 1/3 of a stop or so faster. If both lenses are M lenses OR A lenses the choice doesnt really matter, but, if one of them is an "A" lens, that's the better buy....Robert</p>

<p>I would say yes. Not because of the extra 1/3 stop, but just because in my experience the 1.7 is a better lens overall.</p>

<p>Echoing Jerry, the A 2.0 will cost about $40 and the 1.7 about $75, on either Ebay or PentaxForum. The 1.7 is judged superior and worth the extra.</p>

<p>Get the 1.7 for sure. Just a better lens overall. And a little faster, to boot.</p>

<p>Just to add to what has been said. I have had both the 50mm f2.0 A and f1.7A lens. I can't say that I have a serious issue with the f2.0, but the f1.7 is the better lens, optically and construction. It is not only a little faster, it has a better out of focus background.The f2.0 seems 'less satisfying' as a manual lens to use too. </p>

<p>Math Police here: f/1.7 is 1/2 stop faster than f/2, not 1/3 stop.</p>

<p>I think 1/2 stop more speed is worth the extra dough.</p>

<p>thanks everyone, looks like i will be going for the 1.7, what are the main reasons for going for an A over an M? are they the same optically?</p>

 

<p>Matt, the A version has an A position on the aperture ring and the electrical contacts to allow shutter-priority automatic metering on the A-series and later film cameras.<br>

The A and M versions are optically identical. A bigger difference is that the M version is entirely metal in construction while the A version has a plastic barrel and, significantly, a plastic aperture ring. The notches that create the clicks in the plastic ring wear with use and the ring becomes excessively notchy and difficult to rotate. This may not be a problem if you keep the aperture ring in the A position and meter via the camera body on an A-series or later camera. As I'm a cranky old bugger who prefers to turn an aperture ring, this would be the deciding factor for me.<br>

Here's a useful page. Note the 20g difference in weight between the two versions. <a href="http://kmp.bdimitrov.de/lenses/primes/normal/index.html">http://kmp.bdimitrov.de/lenses/primes/normal/index.html</a></p>

<p>There are two advantages of the Pentax-A lenses over Pentax-M and earlier.</p>

<ol>

<li>You can meter with them normally on a camera with a "crippled" KAF or KAF2 mount. For instance, every Pentax DSLR, and the later Pentax autofocus film cameras. (These cameras cannot read the selected aperture of the lens.) </li>

<li>You can use them in Tv (shutter speed priority) or Program mode on the Pentax SuperProgram and newer cameras.</li>

</ol>

<p>The plastic aperture ring of the Pentax-A is probably the only substantive construction deficit that applies to the Pentax-A lenses as a whole. I don't think the plastic focusing collar matters worth a darn, the helicals inside are all well-made. However, the Pentax-A 50/2.0 is particularly cheaply built.<br>

Also, some interesting Pentax-M lenses weren't replaced by Pentax-A lenses, particularly primes, since the market was moving towards zooms. For instance, there's a Pentax-M 85/2.0, but no Pentax-A.<br>

Note that the Pentax-A lenses can command a pretty premium over Pentax-M lenses due to reason 1 above.</p>

<p>The 50/1.7 M is sharper than the 50/2 M. I have two of the 50/2 M lenses and one 50/1.7 M. If you can loce with the slower speed look for a 55/2 SMC Pentax. It usually sells for less than the 55/1.8 SMC Pentax and seems to be the same lens but with different markings. The 50/1.7 SMC Pentax F is supposed to be even better than the 50/1.7 M. I have one of these which I was lucky to get at a good price. I don't think it's any sharper than the 55/1.8 SMC Pentax but it has newer coating, the A setting and is better than any of the 50/2 Pentax K mount lenses.</p>

<p>Aside from the difference in maximum aperture, the f2 version is supposed to be noticeably inferior in other quality terms than the f1.7 and f1.4 at the same apertures.</p>