Pentax-A versus Pentax-M...What's the difference?

<p>I've had an ME-Super for a very long time now, but I've only recently begun to take it seriously. I'm not well-versed in Pentax info (I use Canons a lot but the Pentax bug is biting me hard!) so I don't know what certain things imply. Is a Pentax-A lens of higher quality than a Pentax-M or vice versa? Is the Pentax-A 50/1.7 more desirable than the Pentax-M 50/1.7 and if so, why? Help me out if you would, please.</p>

<p>Often, they are identical, but some lenses have different versions even with the same aperture and focal length specs.</p>

<p>Optically, you can't say A's are better than M's or vice versa.</p>

<p>The difference is that the A's have an 'A' setting on the aperture ring to allow the body to set the f/stop. Without the 'A' setting, you loose automation and mode support on the DSLR's.</p>

<p>Is the 'A' more desirable? Yes, but not because of optics.</p>

<p>M is without any automation, M is generally slightly inferior because Pentax downsized the glass for compactness.</p>

<p>As in most cases generally doesn't mean always. There are a lot of good M lenses, but like with anything you need to figure out which is the better of the focal length you are looking for.<br>

<br /> <br /> In my opinion, if you are using M lenses, you might as well just buy a few M42 to K mount adapters, and load up on coated Taks, and loctite or crazy glue the adapters. The robustness of the M42s is refreshing, and they are fun to use. </p>

<p> </p>

<p>First, two three sources of info on the lenses. This first one, under Lens Description, will give you charts and optical formulas. So you can see that the M, A, F, and FA 50mm f1.7 are all the same optical formula-<br>

http://kmp.bdimitrov.de/lenses/index.html<br>

User reviews classified by various series-<br>

http://www.pentaxforums.com/lensreviews/index.php<br>

And more user reviews-<br>

http://stans-photography.info/</p>

<p>My general impression from researching the lens and owning some is that the build quality of the lenses has been going downhill all along. So M42 Taks are more solid that Ks which are more solid than Ms which are more solid than As. When you get to the F and FA series, the autofocus mechnisms lead to lots of lighter weight parts and looser feel to the focus rings.</p>

<p>But to repeat what Justin says, general trends don't carry for all models in a particular lineup. Do some research.</p>

<p>One thing to be aware of is that with the digital cameras able to use the A series with metering automation, the As tend to command a premium in price that often far exceeds the quality of the optics. Well, many of the older K-mount lenses get prices a bit excessive. Be careful if you go to eBay or such.</p>

<p>My $0.02 after collecting quite a few M's over the last couple of years--I find them generally better-built than the A's, in particular the aperture rings, which seemed to be more positive and metal on the 'M' lenses. If you're shooting an ME Super, you don't benefit from the extra 'A' features, and you end up paying more because the lenses are more user-friendly on the modern bodies. Same goes for the autofocus 'F' and 'FA' versions.</p>

<p>As for the 50mm, these lenses were pretty mature and didn't change much optically between generations.</p>

<p>Thanks guys! This really helps. I didn't know if I neededto focus on finding A lenses but it seems my M lenses will do just fine. This was most informative, especially the links, Dan.</p>

<p>First go to Boz's site that Dan recommended. You can get a sence there of the optical formulas.<br>

Mechanically I would generally agree with Andrew although I can say I have never had ANY Pentax PRIME lens fail me (I can't say that about a couple Pentax zooms though, both FA). However there is no simple rule to figure out optical quality in comparing between the types (M42, K, M or A). In some cases it would seem that compromises were made for the M series to make them smaller. In some cases the M are identical to A, sometimes even K's are optically identical to A's. You really need to check apples to apples, read through old reviews (or ask here) about specific focal lengths. Of course then you have to deal with all our different opinions and perspectives...</p>

<p>The other point is that we might need to separate zooms vs primes. There are some very good early zooms, but in GENERAL technology (noteably the use of computers to design optics) really helped zoom optics. Even here there are exceptions to the rule. I knew a pro in Kentucky who swore by the 80-200 f4.5 M version ! over version 2 (also an M lens). I likely would never have bought the version 1 because the poor close focusing of the Version 1.</p>

<p>Hi Andy,<br>

Two or maybe three quick things of note. First, in regards to what Justin said here.</p>

<blockquote>

<p>In my opinion, if you are using M lenses, you might as well just buy a few M42 to K mount adapters, and load up on coated Taks, and loctite or crazy glue the adapters. The robustness of the M42s is refreshing, and they are fun to use.</p>

</blockquote>

<p>What a profoundly great statement. I had been wondering why the images out of my Spotmatics seem so much sharper and crisper that what I was getting out of my K mount bodies and turns out the Super Taks where the difference. Also since I do not use hoods with my film bodies, the coating on the super taks does a very good job of controlling lens flare.</p>

<p>I also agree with Andrew. I find the build quality of the M Lens to be superior to the A lenses. On the ME SUPER, as Andrew noted the A makes no difference as the camera is Aperture priority. By the way, I love the ME SUPER, 8-) I always have one with me..</p>

<p>The only camera that the OP mentioned is the ME Super. If that is the camera he is going to use, then it should be noted that the A-series lenses will not offer any advantage. The ME Super does not have the electrical contacts to control the aperture. An A-series lens will work on that camera, just not in the "A" setting.</p>

<p>The M-series lenses were designed specifically for the smaller M-series bodies, such as the ME, ME Super, MX, MG and MV.</p>

<p>Paul Noble</p>

<p>In some case I prefer the slower primes over the fastest image quality wise, for example a M 28/35mm F3.5 over the F2.8 versions. The compact size of the M series is a big plus IMHO, just have a look at that tiny 100mm F2.8...</p>

<p>Andy C., I think you've received all the info you needed, but I will add something else. If you are not planning on moving to digital, then stick with SMC-M lenses due to their smaller size and generally better build. However, if you ever plan to buy a Pentax DSLR, I would recommend that you go with SMC-A lenses whenever possible. They offer nothing extra for your ME Super, but on a digital body they are much easier to use than the SMC-M's.</p>

<p>Somewhat aside, but I am confused about aperture function when using a Super-Tak M42 on a camera like the ME Super, or the MX I own. I understand the M42 to K adapter business.<br /> <br /> But my understanding is that you need to manually stop down the lens to the taking aperture. This can be done as a matter of course, leaving you with a dark viewfinder depending on aperture chosen. Or you can use the A-M lever to stop the lens down right before pushing the shutter, still leaving you with a darkened screen.<br /> <br /> To me, this *is* a real difference between using a K-mount lens of any series and an M42- K-mount adapter. One extra step, having to stop down the lens manually, or having a darkened screen. No automatic stopping down of the lens.<br /> <br /> Am I missing something, mistaken? If not, I do think that should be made clear to people, that there *is* one difference between M42s and Ks on K-mount cameras. Its significance is subject to debate, but its presence is, well, very obvious?</p>

<p>I'll also point out that many M and A lenses are pretty well the same size. For example, the 100mm f2.8 (non-macro) M and A are exactly the same size, with the A being 35 grams heavier. Many other lenses are have the exact same specs, with most likely more plastic in the A compensating for the extra aperture mechanism.</p>

<p> </p>

<p>One of my favorite Pentax M lenses is the 40mm f2.8 pancake lens. Makes my MX pocketable (at least jacket pocketable). I also have the SMC Pentax M 50mm f1.4, 135mm f3.5, and 28mm f2.8. In addition I have the Tamron Adaptall mount to use my Adaptall lenses with it.</p><div></div>

<p>Dan.<br>

You are quite correct. When you use a M42 it is like the lens is already stopped to the aperature it is being used at. So say you wanted to do a landscape at f22. If you set the lens to f22 it would likely be pretty darn dark. If you have critical focusing and are using an f-stop other than wide open you would likely first focus wide open (to see the subject clearly) and then stop the lens down and meter (or use AP) at that new f-stop. However if you can see ok with the lens at the f-stop you plan to use you can get aperture priority out of *most* cameras that offer AP. The exceptions are the Pentax K bodies that are listed as Crippled K, ZX/MZ-50/60, etc. If you have a crippled K body you want to stay away from M42, K and M lenses.</p>

<p>An argument can be made that the M42 glass is in some ways <em>easier</em> to use on digital bodies than K & M glass as you can shoot in aperture-priority mode stopped down whereas old K-mount glass uses a somewhat inelegant and inaccurate stop-down metering solution. I don't know that this is true for the K-mount film bodies where the M glass has better compatibility; here the pre-A M-glass works as designed; Av and Manual modes work with no kludges.</p>

<p>As some of the others mentioned, many of the old manual focus lenses still hold up pretty well against more modern designs, even some zooms. Someone mentioned the M80-200/4.5 and I'd say the M75-150/4 and A70-210/4 are also in that category. Some of the newer ones *may* be better but me and my technique are still the limiting factor most of the time.</p>

<p>Douglas, I don't necessarily expect that these lenses will <em>fail </em> me, just that for many examples, the aperture ring is somewhat annoying and unsatisfying to use. I would go so far as to say that my autofocus F and FA lenses <em>all </em> have smoother and more positive action on their aperture rings than most of the 'A' lenses I own, zoom or prime. I don't own that many A primes (I think most are 50mm) but these aren't so great either. The focus rings are also more likely to have some sort of horizontal play.</p>

<p>I'm sort of under the same belief as what Andrew wrote above me.</p>

<p>I think metering/shooting with the M42s might be easier despite the appearance of it being more difficult. This is even more so if you tend to use the lenses more towards the open end.</p>

<p>Overall, generally K and A lenses sell for the highest premium, with M and M42 seemingly forgotten.</p>

<p>The A function to me is definitely worth a premium, but some of the prices A lenses go for is just absurd. At that point I would ask myself does my photography require A contacts? if not, then look at Taks, if it does than you HAVE to pay the premium.</p>

<p>Generally if I can get a nice A lens, I will go that route if the price is right because I find it to be more functional across a wide range of bodies.</p>