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I took this from a moving bike. To my surprise, only right part of the image (letters) is blurred. I couldn't explain why.

enter image description here

If you need, here's a bigger image with all the metadata.

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  • \$\begingroup\$ In short, you kept aiming at "gandhi" while taking the picture \$\endgroup\$
    – Timo Huovinen
    May 21, 2014 at 16:11
  • \$\begingroup\$ It looks like either rotational blur (the camera was rotating on an axis centered on the least blurred spot) or zoom blur (the lens was zooming in or out and the least blurred spot stayed aimed at the same part of your sensor) to me. If you are moving towards or away from the subject rapidly you can get the same effect as zoom blur. To get the least blurred spot left of center in the image you would have panned left as you moved towards the subject (or panned right as you move away). \$\endgroup\$
    – Michael C
    May 25, 2014 at 20:33

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This is unlikely anything to do with a broken lens. There are two things going on here.

First, you say you were moving at the time this picture was taken. Apparently you kept the lens pointed roughly at the G in GANDHI during the exposure. It therefore makes sense this part of the picture has the least amount of motion blur. Objects more distant from the center of orientation will therefore be more blurred since they go thru more apparent motion over the same small shutter time. You only notice this in the arch to to the right because the left part of the arch is closer to the center of orientation, and the rest of the picture is clouds that are by nature fuzzy and therefore difficult to tell if subjected to motion blur. They are also much further away, so would have less motion blur anyway.

Second, the camera may have been moving more towards the end of the exposure time and your camera has a horizontally-traveling focal plane shutter. In a focal plane shutter, different parts of the image are exposed at different times. If the camera was only moved during one part of the exposure, then only the part of the image exposed during that time will have motion blur.

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  • \$\begingroup\$ Your explanation seems more accurate since the blur there looks more like a motion blur and less like a lens lost focus blur. But one thing about the shutter mechanics you explained. You made it seem like the image gets "scanned" on the sensor. If the shutter speed was 30s, it can't be like it spends first 15s scanning the left half and last 15s scanning the right half of the image! So I take it as there must be multiple passes of scanning going on. And the time taken for these scans must be pretty small. \$\endgroup\$
    – kBisla
    May 17, 2014 at 22:14
  • \$\begingroup\$ So there must be multiple passes and unless the camera moved only through the right half of the scan for every scan, it cannot be explained this way! Sorry if I went too far with this! \$\endgroup\$
    – kBisla
    May 17, 2014 at 22:14
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    \$\begingroup\$ @Blue: The shutter curtains only traverse the image are once per exposure. For slow shutter speeds, the leading curtain crosses to open the shutter, then it waits, then the trailing curtain crosses to close. For fast shutter speeds, the trailing curtain starts to cross before the leading curtain gets to the other side. Each spot is exposed for the specified time, but not necessarily at the same time. None of this has antything to do with how data is scanned out of the sensor. That happens after the shutter closes. This effect works on film too, where there is no scanning. \$\endgroup\$
    – Olin Lathrop
    May 17, 2014 at 22:21
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Now that I took a closer look at home at the larger image and was able to look at the meta data. At 1/10 of a second shutter exposure, the shot was open an exceptionally long time, especially for a moving vehicle.

Since you were traveling, you are seeing the arch as it appeared both at the start and end of the shot as you were moving under it. The clouds remain sharp because they are very distant and thus they changed position very little compared to you.

The G remained sharp because you tracked the shot on the G, however the arch changed orientation significantly in that 1/10 of a second and so you get a blurring of the shot. It is far more obvious when you look at the full resolution version and can see the beginning and end of the exposure clearly.

It has nothing to do at all with which direction the shutter moves as 1/10 of a second is far, far below the sync speed. Your D5100 also has a shutter that travels from top to bottom (note that the camera is upside down in the video).

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