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01-19-2010, 12:00 AM   #1
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fast prime lens

hi everyone

i'm new to pentax, having just bought a Kx with 18-55 and 55-300

i'm now looking on ebay and can see a whole bunch of cheap manual primes, i just dont know whats what.

obviously they're going to be manual focus, which i can put up with if i'm only paying 50-odd quid for the lens, but i think manual exposure is a little much.

can anyone recommend any particular lens, seeing as i dont know anything about them? focal length isnt that important (anything between 28-50 or so is fine), and i'm not to bothered whether it is f1.2 or 2, just something in that region. what i am bothered about is optical quality. are there any lenses that stand out for their sharpness? any help appreciated. thanks!

01-19-2010, 12:14 AM   #2
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Manual exposure is incredibly easy using Pentax cameras. You don't have to dial in the shutter speed through trial and error, like on some other cameras. All you have to do is point the camera at your subject, focus, press the "green button", and then press the shutter button to take the picture. It is incredibly easy and you should really give it a shot. Try out the Pentax SMC-K 55mm f/1.8 or the Pentax SMC-M 50mm f/1.7 to start your adventure, and you will be really really pleased. Each are available for about $55 or 35 quid on average. Especially with the K-x, "manual" exposure couldn't be easier.
01-19-2010, 12:32 AM   #3
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i'm not sure i understand. do you mean that on manual lenses the camera will still adjust the aperture for you?

also, is there any advantage (besides prive, perhaps) of getting one of thos manual lenses, as opposed to AE? i mean is the "A" lens any worse optically than the "M" lens?

01-19-2010, 12:52 AM   #4
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You adjust the aperture on the lens, then press a button, and the camera calculates the exposure. Exposure = aperture size + shutter speed (not mathematically, just mentally). Usually with fully manual lenses, like the ones I'm recommending you pick up, you would have to change the aperture on the lens, then also change the shutter speed on the camera, and get a proper exposure through trial and error. The camera will automatically do the exposure for you once you press the green button.

Basically, the only difference between using an A lens and a K/M lens is that you have to turn a ring sometimes (aperture ring) on a K/M lens, and then press a button. Physically, it's very quick and my speed is not hindered at all versus a manual-focus A lens.

Some A lenses have worse image quality, off the top of my head I can think of the 50/2. But not most of them. However, some also have poorer build quality than their K/M-series counterparts. And, in almost all instances, comparable A-series lenses are about twice as expensive as the K/M counterparts.

Save some dosh, pick up a K/M-series lens, and you won't really be missing anything from getting an A-series or an auto-focus lens. It will also teach you more about photography in the process.

Last edited by wallyb; 01-19-2010 at 01:16 AM.
01-19-2010, 01:01 AM   #5
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If you're not bothered bu f stop or particular focal length, just want to try it out, I would recommed K55/1.8 as Wally did.
They are cheap, and opticaly great. Have great focus throw and are built to excellence.
Good luck
01-19-2010, 01:55 AM   #6
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One downside with K/M lenses

is that you can not P-TTL with your flash. You may be able to trick the camera and make it believe that this is an A, FA, or DA lens. But I have not learned how
01-19-2010, 03:41 AM   #7
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QuoteOriginally posted by yyyzzz Quote
is that you can not P-TTL with your flash. You may be able to trick the camera and make it believe that this is an A, FA, or DA lens. But I have not learned how
True about the flash, but all modern and a lot of older models have "auto" mode. Depending on the price tag/category of the flash, you can have anywhere between 1-4 auto settings. I have two flashes, one with f4 & f8 and one with f5.6 settings. If you manipulate ISO you can shoot at just about any f stop you want...

01-19-2010, 01:09 PM   #8
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I agree that m,anual exposure is much less limitng than manual focus (not that either is rocket science). Set an aperture on the ring , hit green button, take picture. Then take another pciture, and another. You generally don't need to keep changing exposure unless the light changes. As for settings aperture, you really only two most of the time: wide open in low light, f/8 otherwise (obviously, a simplification, but a useful one).

So if an "A" version is available and not much more expensive that the K or M, by all means, go for it. But for many/most lenses, there is either no A version at all, or it's a lot more rare and expensive.

Quality-wise, see or for more info on specific lenses, but *for the most part*, the A and M versions of a lens are optically identical, and both thought of as not *quite* as good as the bigger/heavier K version (or M42 version, if you want to enter the world of screwmount).

01-19-2010, 01:26 PM   #9
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I had a reasonable set of manual focus manual aperture primes before I went digital.

I embarked on a process (otherwise known as LBA) of carefully purchasing only primes that were faster than anything else I already had at any focal leght.

(Note that I have AF zooms covering 28-200mm at F2.8) so purchasing cheap fast primes goes somewhat slowly.

My kit has the following

tamron 24mm F2.5, 28mm F2.5
Vivitar Series 1 85mm F1.4
SMC Pentax 50mm F1.4, 105mm F2.8, 125mm F2.5, 300mm F4, vivitar 400mm F5.6

I am in the process of modifying a vivitar 24mm F2 that I got free with stuck aperture blades from Nikon mount to K mount, and a Kiron 28mm F2 from minolta MD mount to K mount. The 28 mm cost me $5 and it also had stuck aperture blades. This is a common defect of kiron lenses where oil seeps out of the focusing helix grease into the aperture.

K mounts are nice to use in one respect, specifically that everything you do with them is at maximum aperture, but they are not cheap, expecially for fast lenses (i.e. F2,8 or faster.

I have also picked up some M42 lenses, including a vivitar 28mm F2.5, a SMC Takumar 35mm F2, and some longer takumars as well

Again fast Takumar lenses are expensive relitively but off brand ones may be cheap, the vivitar I got for $9.

M42 lenses are interesting on pentax bodies because they can work in Av mode, not just manual like K mounts, but to get the exposure you have to manually stop down.

With respect to focusing, if you are going to get several of these lenses I would explore a split image viewfinder, it makes focusing much easier.

If you want to do flash photography, you have 2 credible options, either get a flash that has it's own auto exposure sensor (like AF 540FGZ) or pick up an *istD or DS body. They are only 6 MP but they have TTL flash capability and work very well with manual aperture lenses.


I have not discussed here the use of SMC-A lenses. the reason, while they are very good MF lenses, the capability to work in Av Mode and with P-TTL flash makes them less than cheap, even compared to K mounts or Takumars

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