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10-04-2010, 11:53 AM   #1
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Half out of focus?

I was recently in Spain shooting with SMC Pentax DA f4-5.8 55-300mm DA. I shot a four shot panorama and on all four shot the left half of the photo was blurred and the right half sharp. I was focused at infinity with the subject landscape more than half a mile away. The lens was zoomed to 170mm and my shutter speed was 1/250. Exposure mode manual. Aperture was f 5.6 and ISO was 100. The left half of the frame on all four shots was miserably out of focus while the right half of the image was sharp. The lens was clean. I am at a loss to understand how one half an image more than a half mile away could be blurred while the other half is sharp.

Ideas?

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10-04-2010, 12:08 PM   #2
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This certainly isn't motion blur or lack of DOF, so I'd say that there might actually be something wrong with your lens. I'd run some controlled tests to check if that's indeed the case!

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10-04-2010, 12:10 PM   #3
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It seems that your lens is decentered... And severely so.
10-04-2010, 12:10 PM   #4
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I had a 28mm Praktica lens that did exactly this because the rear element was loose, and able to pivot. As I'd only paid 20 for it, I just superglued it up.

10-04-2010, 12:27 PM   #5
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Definitely seems like something defective with the lens. Do you notice the same problem with any other lens? If not then can you return the 55-300? Because it sounds like an internal problem with one or more of the internal elements and that is not something you want to try and fix yourself.
10-04-2010, 01:08 PM   #6
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Thanks guys

The problem is hard to pinpoint. I did do a test where I shot some antennae on a hilltop about four miles away. In one shot I pushed the antennae to the right side of the image and in a second shot I pushed the antennae to the left of the image. However, both seemed sharp in the test.

Of course a loose element by the very nature of being loose would not produce consistent results.

Another thought relates to shooting position. I had my left hand on my right shoulder and the lens resting in the crook of my elbow. If I had autofocus on and it was fighting the friction of resting on my elbow, could the mechanism bind and get an element to twist slightly?
10-04-2010, 04:56 PM   #7
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That is a good possibility. Would not take much torque to deflect things. But should the AF not have been done driving the lens when you took the shot?.
I know, this is not helping much.
10-04-2010, 05:41 PM   #8
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Sorry but your image doesn't look particularly sharp overall. Were you using a crappy tripod when shooting the pano? Seriously, before you blame the lens, check that it isn't your other gear that is the problem.

10-04-2010, 07:13 PM   #9
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Unsharp

QuoteOriginally posted by creampuff Quote
Sorry but your image doesn't look particularly sharp overall. Were you using a crappy tripod when shooting the pano? Seriously, before you blame the lens, check that it isn't your other gear that is the problem.
The point is it was a little blurred on one side and very blurred on the other. The shot was handheld at 1/250. It was hand held because I am suffering severe arthritis and was on a 2-3 mile walk and could not carry the extra equipment.

Also I had previously done a series of night shots of 20-30 seconds duration with the camera sitting on a stone wall and tripped with an IR remote. These shots were also unsharp. You don't get much steadier than a stone wall.
10-04-2010, 07:24 PM   #10
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QuoteOriginally posted by Ex Finn. Quote
That is a good possibility. Would not take much torque to deflect things. But should the AF not have been done driving the lens when you took the shot?.
I know, this is not helping much.
I agree that it would no long be driving the lens, but if it had already started to bind, I am not sure it would automatically unbind after the focus motor stopped.

Had it only been one frame and not all four, I would have blamed atmospherics. However atmospherics would not always been on the left in overlapping pano shots.

I am not a big fan of autofocus anyhow as it does a poor job of objects moving directly toward the camera
10-04-2010, 11:52 PM   #11
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QuoteOriginally posted by Roger_H Quote
I was recently in Spain shooting with SMC Pentax DA f4-5.8 55-300mm DA. I shot a four shot panorama and on all four shot the left half of the photo was blurred and the right half sharp. I was focused at infinity with the subject landscape more than half a mile away. The lens was zoomed to 170mm and my shutter speed was 1/250. Exposure mode manual. Aperture was f 5.6 and ISO was 100. The left half of the frame on all four shots was miserably out of focus while the right half of the image was sharp. The lens was clean. I am at a loss to understand how one half an image more than a half mile away could be blurred while the other half is sharp.

Ideas?
Roger I have two 55-300s and they both do this at longer zoom lengths although not as badly as your example. It is particularly noticeable wide open - at 300mm I have to stop them down to the f/8-11 range to get a reasonably sharp landscape image edge to edge. Centre is generally not too bad. Which side is blurred at what FL differs as between the two lenses. I am sure it is manufacturing tolerances, as I got one of them checked out by Pentax in Japan, who said it was 'in spec'. Try the lens at f8 or more - you may find it is better. Of course this is a pain in poor light ...

You may have to get it checked out.
10-05-2010, 10:30 AM   #12
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Timo, thanks for the input, it was very useful. I will test and see what I come up with. I will also be looking at some prime lenses. Maybe I should break out the glass and use the barrel for a pencil holder.
10-05-2010, 04:45 PM   #13
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Are you using any filters on the lens? UV or CPL?
10-05-2010, 05:02 PM   #14
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QuoteOriginally posted by Asahiflex Quote
It seems that your lens is decentered... And severely so.
My first thought as well.

QuoteOriginally posted by timo Quote
Roger I have two 55-300s and they both do this at longer zoom lengths...
My friend has the 55-300 and his is acceptably sharp overall and has none of this one-sided smear.

QuoteOriginally posted by r0ckstarr Quote
Are you using any filters on the lens? UV or CPL?
Good thinking!


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10-05-2010, 11:41 PM   #15
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Steve, not sure where you are headed with the filter question. It is an extra element in the glass stack, but it should not have such a one sided effect. And as far as introducing an even blur, would think this would be minimal with a telephoto where the light would do far less bending than it would with a normal or wide angle where the the lens is reaching out to the sides.

I shot some tests yesterday on a tripod, but I hurried them and the method was not as rigorous as I would like, so I will try again in the near future.

I will say that over long distances no image is sharp unless the air is still, dry, and with moderate temperature.

The telephotos strength is compacting space and managing the size relationship of disparate objects. Otherwise it is best to walk or drive closer to the subject.
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