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03-16-2012, 12:56 PM   #1
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prime lens question

Hi,

Almost made a mistake today by placing a bid on a 50mm lens on ebay.

It is listed as 1:2 and I initially mistook this to be f1.2 (which I'm sure its not). Can anyone clarify what the 1:2 means?

03-16-2012, 01:02 PM   #2
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1:2 means f/2

1:1.7 would be f1.7 etc.
03-16-2012, 01:04 PM   #3
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Ah...

many thanks.
03-16-2012, 01:09 PM   #4
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An f-stop is the ratio between a lens' aperture and its focal length. So if a 50mm lens has a maximum aperture that's 25mm across, the ratio is AP/FL= 25/50= 1:2= f/2. If a 50mm lens has a maximum aperture of 42mm then the ratio is 42/50= ~1:1.2. That wider aperture admits MUCH more light!

Meanwhile, even for us suckers who mistakenly bought a 50/2 thinking it a 50/1.2, there's an easy way to distinguish the lenses: 50/1.2 glass is BIG! And HEAVY! My M50/2 weighs 160g; my K50/1.2 weighs 400g. If a 50 doesn't dwarf its camera, its not superfast, period.

NOTE: This is my 9300th post. I'm crawling up there...

03-16-2012, 01:26 PM   #5
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RioRico- 9,300 posts, that's quite a few. I bet I've read 500 thus far so I still have a way to go. Always some really good information for a lurker like me. So please keep them coming. Here's to another 9,300.....
03-16-2012, 04:46 PM   #6
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Furthermore, it's not uncommon to see a 50mm f/2 lens listed as f/1.2 on eBay. Always check the photo, and make sure it says 1:1.2 on the lens. (Innocent explanation is eBay sellers who confuse 1:2 with f/1.2.)
03-16-2012, 06:22 PM   #7
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QuoteOriginally posted by baro-nite Quote
Furthermore, it's not uncommon to see a 50mm f/2 lens listed as f/1.2 on eBay. Always check the photo, and make sure it says 1:1.2 on the lens. (Innocent explanation is eBay sellers who confuse 1:2 with f/1.2.)
Another hint for Pentax lenses: If it's an M- or F- or FA-series, it ain't f/1.2. The only superfast Pentax 50s are the SMC 50/1.2 (K-series) and the SMC-A 50/1.2 (A-series). No Takumars either. Alas, the eBay search engine can't distinguish between 1:2 and 1.2 so you can't filter bogies that way. So figure that if the bidding is around US$20, it ain't an A50/1.2.
03-16-2012, 11:48 PM   #8
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Thanks everyone. Looks like Its a pretty common for people to get confused by this.

RioRico - thanks. I'm only looking at pentax-a series as really wanted the aperture to work through the body, but this is all good information :-)

03-17-2012, 01:00 PM   #9
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QuoteOriginally posted by mde1970 Quote
Thanks everyone. Looks like Its a pretty common for people to get confused by this.
Yup. Even those of us who think we know something can get burnt. But that's how we learn, eh? We learn good judgment from experience. We gain experience by making bad judgments. An endless cycle...

QuoteQuote:
RioRico - thanks. I'm only looking at pentax-a series as really wanted the aperture to work through the body, but this is all good information :-)
There's a paradox or GOTCHA! here, to wit: Pentax K- and M-line lenses are slightly more difficult to use than A-line, but ordinary A-line lenses are considered to be not so good build-wise, especially compared to K-line glass.

The common view is like this: Pentax made superb Takumar screwmount lenses. Their original K-liners were often just Takumars in bayonet mounts, supplemented by a few superlenses like the K50/1.2. K-liners tends to be HEAVY and SOLID. Then Olympus released the OM-1 and Pentax decided to to compete with their M-series, so M lenses tend to be quite small, with different+slower optics. Then Pentax decided to upgrade the aperture control and reduce costs, and so released the A-line with electric contacts and more plastic parts. Read the user lens reviews and see how often PLASTIC appears under CONS.

I'm not talking about the A* and Ltds, which are always premium gems, nor about 3rd-party lenses, which can be all over the place quality-wise. But non-premium A-liners are usually valued more for their ease of use than for their build and feel and look. Caveat emptor.

Last edited by RioRico; 03-17-2012 at 01:08 PM.
03-17-2012, 01:59 PM   #10
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QuoteOriginally posted by RioRico Quote
Pentax K- and M-line lenses are slightly more difficult to use than A-line, but ordinary A-line lenses are considered to be not so good build-wise, especially compared to K-line glass
While I agree with the gist of this, for me the A-series build quality is fine. Yes, the K-series lenses in particular have a "they don't make 'em that way any more" feeling of superb craftsmanship, but in my limited experience even the rank-and-file A-series lenses are well built. And I guess I can't tell the difference between metal and plastic, because I can't detect any plastic parts in any of my A lenses. I was initially put off by all the negative comments about the A-series build quality, but for my purposes I needn't have been.
03-17-2012, 02:31 PM   #11
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QuoteOriginally posted by baro-nite Quote
While I agree with the gist of this, for me the A-series build quality is fine. Yes, the K-series lenses in particular have a "they don't make 'em that way any more" feeling of superb craftsmanship, but in my limited experience even the rank-and-file A-series lenses are well built. And I guess I can't tell the difference between metal and plastic, because I can't detect any plastic parts in any of my A lenses. I was initially put off by all the negative comments about the A-series build quality, but for my purposes I needn't have been.
Certain of the "ordinary" A-series lenses are outstanding both in build and image quality - the A35~105/3.5 for instance. I have thought about selling almost every lens I own at one time or another except that and the FA35/2.
03-17-2012, 03:38 PM   #12
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Say what you want about the A lenses.

Then take a look at the pictures I've gotten with my favorite 50mm 1.4. (It's the one I usually use with my binocular lens rig.)

'Nuff said.
03-17-2012, 06:57 PM   #13
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Please note that I said that ordinary A-line lenses are *considered* somewhat inferior build-wise, not that they *are* inferior. I'm just reporting what I've read; I haven't used enough A-liners to make a judgment. Still, a couple of my lousier zooms have been A-line: A28-80/3.5-4.5, and what's arguably the worst lens Pentax ever produced, A35-80/4-5.6. That last is decent when reversed for macro use; but straight up, it sucks. And it has the cheapest plastic feel. A sorry excuse for a kit lens...
03-17-2012, 07:17 PM   #14
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Perhaps it's fair to say the Pentax-A series is a mixed bag, both in terms of build and optical quality. My experience is limited to the A lenses in my sig.
03-18-2012, 09:50 PM - 1 Like   #15
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Ok, now that the A bashing has started I have to weigh in, as far as A goes build wise its all metal in the parts that count (the guts with the gears), they made some of the exterior decorative pieces and the aperture rings out of plastic, given the choice between F'ing around with the damn green button and the aperture ring in my all metal K or M lens or just spinning the front and rear dials on the camera to control shutter speed and aperture while getting exposure info from the camera with an A lens, I'll take an A over a K or M any day.

If you are talking about A zooms, all the variable apertures are trash, don't even bother getting them cheap, most of the fixed aperture A zooms are good to really great. The primes are all of excellent quality, though some are slow enough to be a waste of time like the 50mm F2, the bane of my freaking existence since it totally clogs Ebay with crap lenses while I am searching for good stuff. A* lenses are not worth the money, for that much cash go for a newer lens series.

As far as the fast 50's in A go, don't settle for F2, the F1.7 is fine if you are poor, the F1.4 is ideal in my book for both price and speed, the F1.2 is dreamy fast but so stupidly expensive that you'd be afraid to take it out of the safe, and so I don't consider it worth it or even realistic to ever own one.
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