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03-16-2012, 10:51 AM   #1
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Pentax A-Series lens question

This is the first time I've used a Pentax brand dslr (K-x) and need a little guidance on something regarding older lenses. I am looking to purchase a prime lens (my other two lenses are zooms), and have come across a Pentax A-50MM f2 at a very reasonable price.

It is my understanding that the A series is one of the older Pentax lenses and designed for film cameras. If I were to use this as my prime lens (until I can afford a newer and better DA series prime) on my K-x, are there major limitations or concerns I should be aware of before I head down this path? Just like to know before I spend my money.

My interest in getting a fast prime lens is due to my desire to get outdoor shots with shallow depths of field (plants, wildlife), and also getting good shots in low-light or indoor situations. Ideally I'd like to get fast zoom lens, but that is definitely out of my price range at the moment. Therefore, my thinking is that the A series prime mentioned above will be a good temporary compromise.

BTW, I also believe the
A-50MM f2 is NOT an autofocus lens, meaning I would have to set the camera to manual focus prior to shooting, correct?

Greatly appreciate anyone's thoughts on the matter, especially from those who have used older series lenses on the K-x. Thanks!


03-16-2012, 11:01 AM - 1 Like   #2
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A 50/1.7 on K-5

Bonjour,

I use the above in manual focusing and "Av" setting ... works great. I do not have any experience with a K-x, but should be the same ...

Also, you may find that a fixed focal length forces you to think about your composition, etc. The f2 should be good ... get it, experiment and enjoy.

Salut, John le Frog

Last edited by Jean Poitiers; 03-17-2012 at 03:06 AM.
03-16-2012, 11:05 AM - 1 Like   #3
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QuoteOriginally posted by Stardog Quote
BTW, I also believe the A-50MM f2 is NOT an autofocus lens, meaning I would have to set the camera to manual focus prior to shooting, correct?
No, you do not have to change anything on the camera, as there is no connection to the AF system at all (mechanical or electronic). The camera will automatically be in manual focus mode, no matter what the AF switch says (same with all other manual focus lenses).

Last edited by Cannikin; 03-16-2012 at 11:13 AM.
03-16-2012, 11:07 AM - 1 Like   #4
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Pentax-A is the 3rd series of Pentax K-mount lenses and cameras. The first two, K- and M-series (lenses labeled "SMC Pentax" and "SMC Pentax-M", respectively) have no electrical communication between lens and camera. The A-series mount introduced electrical contacts for transmitting aperture data. So an A-series lens can be used in any exposure mode on your K-x; you simply have to put the lens's aperture ring to the "A" position, and enable this setting in your camera. You're right that A series does not have autofocus.

The Pentax-A 1:2 50mm was the kit lens for several years and these lenses are ubiquitous and not in high demand, so you shouldn't pay much for one (I'd suggest US$35 as a max, and you should be able to find one for quite a bit less than that). It's a fine lens but the Pentax-A 1:1.7 50mm is worth considering as an upgrade.


Last edited by baro-nite; 03-16-2012 at 11:08 AM. Reason: typo
03-16-2012, 11:17 AM - 1 Like   #5
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QuoteOriginally posted by Stardog Quote
BTW, I also believe the A-50MM f2 is NOT an autofocus lens, meaning I would have to set the camera to manual focus prior to shooting, correct?

Greatly appreciate anyone's thoughts on the matter, especially from those who have used older series lenses on the K-x. Thanks!
If you set Catch-In-Focus (Custom Menu 3 Item 21) to On you can leave it set to AF. The camera will not take a picture until you get a focus confirmation or set the camera to MF. This acts as a kind of poor man's autofocus.
03-16-2012, 11:28 AM - 1 Like   #6
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QuoteOriginally posted by Stardog Quote
It is my understanding that the A series is one of the older Pentax lenses and designed for film cameras. If I were to use this as my prime lens (until I can afford a newer and better DA series prime) on my K-x, are there major limitations or concerns I should be aware of before I head down this path? Just like to know before I spend my money.
There are no limitations except that you have to focus manually. All automated and all manual shooting modes can be used.

BTW, the 50mm F2 is sort of a poor lens. I would opt for the F1.7 version instead, as it's still quite cheap.

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03-16-2012, 11:37 AM - 1 Like   #7
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As noted above the 50mm f/2 is not by any means the best of the Pentax 50mm lenses. It will certainly work provided you enable "Allow aperture setting other than A" in the menu and the price is certainly attractive. See here for more information on using manual Pentax lenses.

Pentax also made 50mm f/1.7 and 50mm f/1.4 versions. Both are good with the 1.4 commanding a premium price but still very reasonable. See here for reviews of the various Pentax-A primes.

I have f/1.4 version and used it on the k-x and now on the k-5 with good results.

There is also an f/1.2 version but that is very pricey going for at least $500 and usually more.
03-16-2012, 11:41 AM - 1 Like   #8
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QuoteOriginally posted by jatrax Quote
As noted above the 50mm f/2 is not by any means the best of the Pentax 50mm lenses. It will certainly work provided you enable "Allow aperture setting other than A" in the menu and the price is certainly attractive. See here for more information on using manual Pentax lenses.

Pentax also made 50mm f/1.7 and 50mm f/1.4 versions. Both are good with the 1.4 commanding a premium price but still very reasonable. See here for reviews of the various Pentax-A primes.

I have f/1.4 version and used it on the k-x and now on the k-5 with good results.
+1 Reading the referenced thread is the best advice in this series of replies. Your camera is intentionally designed to support your manual focus efforts with "A" series Pentax lenses (and all the others, too). You will find all the resources you need to make great images on Pentax Forums!!

03-16-2012, 11:51 AM   #9
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QuoteOriginally posted by jatrax Quote
As noted above the 50mm f/2 is not by any means the best of the Pentax 50mm lenses. It will certainly work provided you enable "Allow aperture setting other than A" in the menu and the price is certainly attractive. See here for more information on using manual Pentax lenses.
While doing this is generally a good idea (there is no downside to it, and essential if you use M or older lenses), it is unnecessary to do any of this with an A (or later) lens, as there is no point in shooting in anything other than A.

Set the lens to A and you can forget that the aperture ring even exists. Put it on your camera with no changes to any setting and it will work just like any other modern lens, except that you have to manual focus (and enter the focal length on startup for SR to work).
03-16-2012, 11:53 AM   #10
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After I posted this reply, others had responded and basically all of my questions have been answered. Many thanks to all.

Gary

QuoteOriginally posted by baro-nite Quote
you simply have to put the lens's aperture ring to the "A" position, and enable this setting in your camera.
Baronite: When you stated in your reply "...and enable this setting in your camera," what exactly are you referring to. Just so I know what you mean (instead of thinking I know what you mean). .

From the feedback I am getting re: the A-50MM f2 lens (or an upgrade to an A-1:1.7 50mm), it sounds like it should be a more than acceptable lens to use for the purposes I want (i.e. experimenting using a fast prime lens). However, due to the fact they seem to be so common and the prices extremely reasonable, it doesn't necessarily mean there will be a noticeable negative impact on image quality, correct? I am well aware of the old adage you get what you pay for, but sometimes there are diamonds in the rough. Just want to make sure I won't be sacrificing several degrees of quality picture taking by using this particular lens.

Again, everyone has been extremely helpful and I greatly appreciate everyone's thoughts. This is a great forum.

Last edited by Stardog; 03-16-2012 at 11:56 AM. Reason: Updated info
03-16-2012, 12:07 PM   #11
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Much good advice and info above. I'll agree on the A50/2 lens -- if it's under US$25, grab it -- if it's more, look for an A50/1.7 -- or if you can push your budget further, get an A50/1.4.

Since your goals are DOF control and low-light shooting, faster is better. Any 50/1.4 lens can do amazing things -- but you'll get thinner DOF (at a greater distance) with a cheap 135/2.8.

Yes, as long as its aperture ring is at the A setting, an A-type lens works totally automatically except for focus. And manual focus (MF) is no big thang to learn -- or use Catch-In-Focus.

Yes, if you enable Catch-In-Focus (CIF) you can leave the AF switch at AF-S to enjoy this poor-guy's autofocus. My delaminating eyeballs depend on CIF to nail shots with my MF lenses.

No, CIF isn't restricted to A-type lenses. It can work with any MF lens (as long as the lens mount contacts are covered), and with AF lenses too: Hold the lens-lock button while shooting.

Good luck and have fun!
03-16-2012, 12:10 PM   #12
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The A50/f2 was a kit lens with Program cameras. It is a Pentax lens. It has fine optics, perhaps some construction shortcuts and a limited maximum aperture. For your purposes, at the going price, it is a fne lens to start with.

A50/2 Lens Review - 46 opinions are posted here.
03-16-2012, 12:22 PM   #13
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QuoteOriginally posted by RioRico Quote
Yes, if you enable Catch-In-Focus (CIF) you can leave the AF switch at AF-S to enjoy this poor-guy's autofocus.

On the K-x, that would just mean setting the AF/MF switch by the lens mount to AF,
and making sure that you have AF mode set to AF.S or AF.A.
03-16-2012, 12:25 PM   #14
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QuoteOriginally posted by Stardog Quote
Baronite: When you stated in your reply "...and enable this setting in your camera," what exactly are you referring to. Just so I know what you mean (instead of thinking I know what you mean). .
Mistake on my part -- I had misremembered the nature of the "aperture ring mode" setting in the camera. Cannikin has it right; for an A-series lens you can just leave the lens on "A" and it will work. To use a K- or M-series lens, or to use the aperture ring on an A lens, you'll need to change the "using aperture ring" setting to "permitted".

The Pentax 50/1.7 in all its iterations (M, A, F, and FA) is considered one of the best values going in terms of optical performance for the price. The Pentax 50/2 optical formula isn't as well regarded, although some feel it's underrated. It is considered an adequate performer.
03-16-2012, 02:42 PM   #15
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Thanks a lot for all the good info sent my way. I've learned a lot in a short period of time and have decided to first search out the Pentax 50/1.7 instead of the Pentax A-50MM f2. Sounds like more bang for the buck and more useful for my experimentation needs as I delve into the world of faster lenses. Plus, it allows me to put one of my tried and true principles into action. If you have a choice between two inexpensive (i.e. cheap) items, always choose the highest quality cheap item. Words to live by (at least until I win the lottery).
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