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03-17-2012, 08:58 AM   #1
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different lens behavior in viewfinder and live view AF

i bought pentax k-r camera, i start to take photos in manual mode auto focus. when i take photo using viewfinder i can see red square focus point and it beeps and when i release shutter button i do not hear any lens zoom noise or focus doesn't zoom, but when i take photo through live view then i can see zooming on screen and zooming noice on lens. so my question is why it doesn't zooming and noice of zoom happen when i take photo through viewfinder same like it happends when i take photo using live view. is it faulty ??? thanks a lot for replies in advance.

03-17-2012, 10:10 AM   #2
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This is because a different AF system is used via the viewfinder and via live view. The one in the viewfinder is called phase detect AF, and it's generally much faster than the contrast detect AF used in live view. The key difference is that phase detect can calculate the correct "lens zoom" whereas contrast detect uses trail-and-error to an extent.

You can read more about phase detect AF here: Fixing Front and Back Focus - Causes of Front- and Back-Focus - PentaxForums.com

BTW, I deleted your duplicate thread in the other forum. Please don't post the same question twice

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03-17-2012, 11:15 AM   #3
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The AF is different.
The phase AF that's use with the viewfinder is smarter, it knows when something is in focus and if not which way to move that's why it doesn't move.

The AF with live view use the contrast in the image and to know where the point of maximum contrast is it needs to move the focus and that's why it always move.

The AF in liveview is more accurate because it use the real image but the phase AF is faster and smarter, you don't want to the liveview AF for something moving but for not moving subject or portraits it can be quite handy though, you also see the focus much better on the big screen.
03-17-2012, 04:01 PM   #4
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When you see the red square in the viewfinder, the camera is locking focus on that spot. When you see the green hexagon in the bottom of the viewfinder, that means it has what it "thinks" is a solid focus lock. Think about how a viewfinder works for a moment. It's a "TTL" system, which means quite literally Through The Lens. When you half press the shutter release to acquire focus, you'll see the image projected in the viewfinder go from blurred to clear (hopefully), and then it will beep. You are looking directly through the lens.

That's the equivalent to the green box in live view zooming in and grabbing focus. The main reason it does that in Live View is so that you can move the location of the box with the d-pad (or move the camera), reacquire focus, and see more of what you're focusing on in the LCD. In this case, you are looking at what the sensor sees.

The zoom effect you see has nothing to do with the focal length of the lens. The lens isn't really zooming in, the camera is digitally enlarging the image on the LCD, so obviously this isn't possible with a glass viewfinder that you actually lets you look through the lens.

03-18-2012, 06:12 AM   #5
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these are great replies from great people, thank you very much all of you above, it will help me lot. this place is very good with very good people. i have one more question which making me disappoint on my buying decision. i bought this good camera from ebay its brand new, when i received the parcel, the pentax box was not company sealed and when i took camera off the box and moved it side by side and upside down, i hear some noice inside camera moving into it. is it because shake reduction sensor or something else, is it normal or something wrong. i am very happy with camera but i m thinking i should have bought from local shop.
03-18-2012, 08:32 AM   #6
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Perfectly normal. Enjoy your camera.
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