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05-01-2015, 10:50 AM   #1
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Problems with the focus of PENTAX SMC FA 50mm 1:1,7

Hello everyone.

I own a Pentax K5-II, a FA 50 1,7 Lens and a Tamron 17-50 2.8.

When shooting with the Pentax FA50 I encounter very many unsharp images. It does not always fail, but its too often to accept it. Its very annoying. The Tamron Lens at 50mm works just fine, the FA-50 not. Here are two examples of a shot with FA50. One is sharp another one not, same lens though. It is not even stepped down to 1.7. The shots are at 2.8.

I ask myself if I got a bad copy of this lens or if its just a shitty lens altogether?

Cheers
MP

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05-01-2015, 11:23 AM   #2
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My FA 50 1.7 is one of my favorite lenses and works great. The first shot looks like it front-focused. Are you selecting the focus point or letting the camera pick? Try selecting the focus point and see if it improves. Also, you may need to fine tune autofocus in the camera. You can get a test kit, or simply lay a ruler at an angle to the camera and focus on a line. If actual focus is in front of the line the camera indicated in focus, then the combo is definitely front-focusing and you'll need toadjust in the camera menu.

Last edited by jrpower10; 05-01-2015 at 12:21 PM.
05-01-2015, 02:27 PM   #3
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Are you able to manual focus and get sharp images with the FA 50/1.7? If not, the lens has optical issues.


Steve
05-01-2015, 03:27 PM   #4
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My copy is great, though I'll admit the focus is not as reliably accurate as my DA limited lenses. Having said that, these appear to be taken in bright sunlight so it's hard to imagine any camera's AF system failing in that situation.

Have a look at the link below, print the chart and check the focus with the lens wide open. It may be that it needs some adjustment. You may be able to do that on the camera, depending on the model, or you may need to send camera & lens Pentax to adjust.

http://www.efoto.lt/files/focus21.pdf

05-01-2015, 06:53 PM   #5
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This is one of the sharpest non-macro lenses Pentax has ever produced. The first shot is obviously misfocused, so for some reason the lens isn't playing well with the AF of the camera. Since it's a screw drive lens, if you are not getting binding in the AF mechanism or a similar mechanical failure, then it's likey the camera that's having the problem determining correctly when it has achieved focus. What are your AF settings? If you are shooting in multipoint CAF, it could be that it's bouncing between focus on different points in the image, resulting in some focused on the intended subject and some on wrong objects in the frame.
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