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02-10-2013, 10:40 PM   #1
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Problem with lens or me?

I've had the 50mm M f1.7 lens for a while. However I have just recently started to really practicing using it, trying to get better with MF. Something I don't quite understand is often, images that I expect to be 'easy to take' because of large DOF, focus at infinite, often turn out to be blurry mess. I do notice the lens is fairly prone to CA. Will a hood help with the problem here or is the lens defective in some way or is something else going on?

In the first picture below, I basically focused on the house, which I'm sure was at infinity, using f5.6. I expect almost the entire picture should be fairly sharp. But it looks like a mess.

In the second photo, also f5.6, I was focusing on the tree which turn out to be reasonably sharp. However, the yellow flower look very unpleasant to me.

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02-10-2013, 10:56 PM   #2
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first photo is severely front-focussed while the second photo makes it hard to believe that it's at f/5.6, considering how relatively shallow the DoF is at that distance. Just a few checks first:
Is your diopter on your body adjusted for your eyes?
Are you shooting in M mode?
Did you turn on the setting in the menu that enables use of the aperture ring?
02-10-2013, 10:59 PM   #3
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The diopter is correct. I was shooting in Av mode, would M mode make a difference? And yes aperture ring is enabled..
02-10-2013, 11:21 PM   #4
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QuoteOriginally posted by ruggiex Quote
The diopter is correct. I was shooting in Av mode, would M mode make a difference? And yes aperture ring is enabled..
You need to be in M mode with an M lens, otherwise it stays wide open. You were really at f1.7 in this case.

02-10-2013, 11:27 PM   #5
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You could have a lens that focuses past infinity - ie, just cranking the focus all the way isn't actually going to give you what you want.

If you shoot in AV with a manual lens the camera is just going to shoot you wide open, so you (probably) shot both of those at f/1.7 which could explain a bit of the blur though fast fifties tend to be sharper than that even wide open. The fact you're shooting wide open also would explain the CA tendency - stopping down usually clears that up a bit if not entirely.

What you need to do is set the camera to M, compose the shot, hit your green button so the camera knows what exposure to take at 5.6 (or whatever you're at) and then see how your results go. They *should* improve over that, and if not you could have a dud lens.

As far as the shooting 1.7 goes, you can see it in the tree shot. Your depth of field is very narrow - the tree and the flowers immediately beside it are in focus, the rest is blurred. The shot with the barn is just plain front focused. You weren't at infinity on that one.

Last edited by Sagitta; 02-10-2013 at 11:47 PM.
02-10-2013, 11:38 PM   #6
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Thanks, I was always under the assumption that Av mode would work just fine but I guess that's only for A lenses. Just ran some tests and I can definitely see the differences.
02-11-2013, 12:05 AM   #7
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There are DOF markings on the lens. At f5.6 40-45 feet to infinity should be in focus.
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