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04-28-2010, 07:40 AM   #1
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What is a good aperture rating for a zoom lens (or any lens)?

I bought a Pentax k-x and wanted to get a manual lens for it. I've seen a lot for sale but didn't know a good f-stop or aperture rating that I should be looking for.

If this should be in the beginner forum please let me know. thank you.


Last edited by justtakingpics; 04-28-2010 at 08:09 AM.
04-28-2010, 10:01 AM   #2
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for a general use zoom look for f2.8, fixed - that means that at any focal length the glass could stay at f2.8. Cheap zooms vary the aperture with the focal lenght.

for a prime f1.4-f2.8 are good.

the lower the f usually the higher the price so ... your choice.

an absolute must for you is a 50mm prime which is reasonable as a portrait lens or a moderate telephoto.

buy and read the Scott Kelby digital photography volume 1, 2, 3 and you're set!
04-28-2010, 10:06 AM   #3
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Your first manual should be a Pentax Super or SMC Takumar 55mm 1.8--real cheap at around $25 to $35 and easy to find on eBay. You'll need an adapter to M42 screw mount, which is cheap enough too.

Great lens for the money, and you'll be a part of history. (Made in the late 60s and early 70s.)

If you want to go for a little more bucks, look for the same in a faster 50 1.4, which is going anywhere from $75 to $125 these days.
04-28-2010, 11:13 AM   #4
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why is 50mm important?

04-28-2010, 12:30 PM   #5
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It's not, particularly, for your dSLR, but it was for film cameras, because it was the so-called "normal" field of view (prints made this type of lens when viewed froma typical distance show objects the same sizes as they would have appeared in real life). On a DSLR, it's 35mm that serves this function. The best thing about 50mm lenses today is that they are cheap, because they *used* to be so important that so many more of them were made. And they do work out well for portraits, and some like them for other things too.

I would definitely recommend a good basic beginning book on photography - it will explain many of the these concepts quite thoroughly. The concepts are so universal that it pretty much doens't matter which book you choose - whatever the library hapens to have in that day will be fine.
04-09-2011, 12:43 PM   #6
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Hi Ira
quick question where do I get a good but cheap M42 screw mount adapter from? Does brand matter?
04-09-2011, 04:12 PM   #7
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Thread Necromancy.....

https://www.pentaxforums.com/forums/pentax-lens-articles/110657-how-use-manua...7-k-x-etc.html

If you are not modifying large numbers of M42 lenses avoid the cheap adapters. Get a genuine Pentax Adapter K and you won't be sorry.
04-09-2011, 06:32 PM   #8
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The genuine Pentax adapters are around $30, probably a little more now, and are available from Pentax.

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