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05-09-2010, 04:39 AM   #1
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pentax 50mm f2 A lens focus problem :(

i bought a 50mm f2 A lens for 36 dollars a week ago and the problem is i cant take clear shots. everysingle shot i took seems like out of focus :/ i tried on a tripod even but got the same result.. im pretty sure what i see at viewfinder of camera and im also sure focus was ok :/ is the problem about me (may be im not focusing good enf) or my k100ds or lens . i also read n tried all methods mentioned in other posts at pentaxforums .any help and advice is welcome

http://img413.imageshack.us/img413/5831/imgp1865.jpg
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05-09-2010, 05:57 AM   #2
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I've looked at two shots and they looked fine. They just show a very shallow depth of field. If you want more things to be in focus, you need to stop the lens down to a higher f-ratio.

Notice that focusing at f/2 with the stock focusing screen is hard as it will always show you a DOF that is equivalent to f/2.8. So it is easy to miss the exact spot as things will appear to be in focus while they are not.

Perhaps tell us a bit more what you are looking for and what you are doing when taking photos.
05-09-2010, 08:05 AM   #3
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What Class A said.

But also, if it's anything like my older Pentax 50mm f/2 (the K1000 "kit lens"), it's not a very good performer wide-open. Stop down to at least f/5.6 for best results -- not just in terms of DoF.
05-09-2010, 08:08 AM   #4
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Good Morning,

I took a look at a few of your images, and they all seem to have one item in common - f2. When the lens is opened up all the way, you are going to be playing with depth of field. Depth of Field (DOF) is a function of both aperture, focal length and distance between the lens and the target. The larger the aperture (or smaller the f#) the narrower or more shallow the DOF.

So, what does that mean. At f2 with your 50mm lens at 2 feet, your DOF is 1/2 of an inch. Thus, you will have 1/2 an inch of what every you are focused on, sharp and everything else blurry to some degree. This is called brokeh. Check out this DOF calculator and play around with it a bit....
Online Depth of Field Calculator
Also, here is a wonderful explanation...
Understanding Depth of Field in Photography
..... hope that helps.


05-09-2010, 09:16 AM   #5
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brokeh : coining a term

QuoteOriginally posted by interested_observer Quote
So, what does that mean. At f2 with your 50mm lens at 2 feet, your DOF is 1/2 of an inch. Thus, you will have 1/2 an inch of what every you are focused on, sharp and everything else blurry to some degree. This is called brokeh. [...]
Heh.

Bokeh: the characteristics and rendering of the out-of-focus areas of a photograph

Brokeh: portions of a photograph which are blurry because the photographer selected an aperture which does not provide sufficient depth of field.
05-09-2010, 09:25 AM   #6
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thank you all for the information first of all i want dof to be shallow my general usage of this lens will be shooting portraits of women and babies. so being soft at wide open is also what i want. my problem is lens is not performing as it should about focusing the correct object.and it doesnt focus on something at back or front
that sample images are taken at min distance with focus assistant and af mode on. so do u say i would try harder with this lens or should i get another model of pentax manuel lenses. i have oportunity to get 50mm 1.7 m from a friend.
05-09-2010, 10:06 AM   #7
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QuoteOriginally posted by deathdream Quote
thank you all for the information first of all i want dof to be shallow my general usage of this lens will be shooting portraits of women and babies. so being soft at wide open is also what i want. my problem is lens is not performing as it should about focusing the correct object.and it doesnt focus on something at back or front
that sample images are taken at min distance with focus assistant and af mode on. so do u say i would try harder with this lens or should i get another model of pentax manuel lenses. i have oportunity to get 50mm 1.7 m from a friend.
I'm having a hard time understanding your complaint. The images all look to have something in focus. And if your complaint is that the focused item isn't sharp enough, that's what "being soft at wide open" means.
05-09-2010, 11:19 AM   #8
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QuoteOriginally posted by deathdream Quote
my problem is lens is not performing as it should about focusing the correct object.
So you are saying you tried to focus on oe object, but a different object appeared in focus in the actual picture? Mostly that's just a matter of practice. The big issue is tha the viewfinder shows you *too much* in focus when shooting at f/2. You can test this easily by shooting some text at an angle - see how lines appear in focus in the viewfinder, then see how many lines are in focus in the picture. You should find *more* looks in focus in the viewfinder than in the picture at f/2. So unfortunately, it's normal some things that appear in focus to turn out not to be. With practice, you can learn to work around this and make sure the object you care about remains in focus. or you can get a split-prism focus screen to replace the stock one, and that will solve this problem.

QuoteQuote:
that sample images are taken at min distance with focus assistant and af mode on.
You can't rely on that when dealing with very shallow DOF, because all it is telling you is that *something* near the center of the image is in focus. You can't guarantee focus is *exactly* where you want it to be.

05-09-2010, 11:55 AM   #9
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im getting to the point :] sorr1 for misunderstanding, i ment focused obj. is kinda blurry. but it focuses almost where it shows.i ll upload images for f5.6 n f8 tomorrow they arent as sharp as any sample image i ve seen on web :/
i might consider to buy a split screen but i want to be sure the problem is just me :] not camera or lens
have been searching , but ppl telling me to buy 1.7 or 1.4 for wide apertures.and commonly they say this lens is so soft till f5.6 eventho i like the build of lens so much

Last edited by deathdream; 05-09-2010 at 12:08 PM.
05-09-2010, 05:56 PM   #10
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QuoteOriginally posted by deathdream Quote
im getting to the point :] sorr1 for misunderstanding, i ment focused obj. is kinda blurry. but it focuses almost where it shows.i ll upload images for f5.6 n f8 tomorrow they arent as sharp as any sample image i ve seen on web :/
i might consider to buy a split screen but i want to be sure the problem is just me :] not camera or lens
have been searching , but ppl telling me to buy 1.7 or 1.4 for wide apertures.and commonly they say this lens is so soft till f5.6 eventho i like the build of lens so much
Well, there are faster and sharper-wide open lenses in the A series, you might try the 1.4 if you like a portraitey thing.

Also, for your portrait use, try adding a stocking or a diffuser to that f2 one when it's open wider: sometimes lenses that may not be so sharp wide open actually become pretty cool if you do that. From the look of one of your shots there, this may be one of them.
05-09-2010, 06:00 PM   #11
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QuoteOriginally posted by deathdream Quote
im getting to the point :] sorr1 for misunderstanding, i ment focused obj. is kinda blurry. but it focuses almost where it shows.
And that's what "soft wide open" means.

QuoteOriginally posted by deathdream Quote
i ll upload images for f5.6 n f8 tomorrow they arent as sharp as any sample image i ve seen on web :/
Ah, see, now, that's a different issue. Have you tried aggressively unsharp-masking them?
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