1

Context

This are images from my recent air show. All was taken at (210mm, f/6.3, 1/1250, ISO100) using the 55-210/4.5-6.3 lens on my Sony a6000.

Question

Is that vignetting or something else happening to some of my images? I often see the vignetting similar to the 2nd image from the top but what is going on in the 1st and 3rd image?

Update

No filters are used in the shots below and the images posted are the full image just scaled down. For shot #3 that was in a burst and only that shot, out of the others, has that issue.

Bad Plane Shot Good Plane Shot Something else?

  • 1
    Are any of these shots cropped? Or uncropped? – Michael C Oct 11 '15 at 21:01
  • You've asked some questions recently asking for filter recommendations and advice... any filters in use here? – mattdm Oct 11 '15 at 21:08
  • I didn't use any filters and these are not cropped. Only scaled down to fit. – unsignedzero Oct 12 '15 at 0:38
3

The first two look like typical light falloff at the corners that is normal for telephoto shots taken with a wide open aperture. Even though the aperture is f/6.3, that is as wide as that lens goes. With the darker the sky the falloff will be more noticeable due to the way light curves and gamma are applied to the linear data coming off the sensor. In the first image the differences between center and corners are emphasized because they fall on the part of a typical response curve that has the steepest slope between the two intensities. With the brighter sky in the second shot the differences are minimized because the slope of the light curve levels out quite a bit near the top.

The third shot, however, looks like your lens hood or another obstruction was blocking the top edge of your lens.

  • For the third shot, does moving up and down quickly with the hood cause that? The shot before and after that, in a burst, don't seem to have that. – unsignedzero Oct 12 '15 at 0:42
  • If the hood was not properly attached it could have moved. Were you standing under a canopy, umbrella, or tent? Where the shots with the obstruction at times when your camera was pointed the highest? – Michael C Oct 12 '15 at 2:27
  • The hood is locked on and no I was outside in the sun. – unsignedzero Oct 12 '15 at 17:50
  • I've had occasions where I thought the hood was properly snapped into place only to discover it was not. There is clearly something obstructing the optical path in the third photo. – Michael C Oct 12 '15 at 18:29
  • Wearing a hat with a long visor? – Michael C Oct 12 '15 at 18:30
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Never seen such pronounced vignetting on a telephoto lens. I would assume then that something is wrong. Any one of these could be possible:

  • Lens hood in the wrong orientation . The largest petals should be top and bottom.
  • Wrong hood. That happened to me before. Some lenses have the same diameter but hoods are not interchangeable as they are highly dependent on focal-length.
  • Filter too thick. Some lenses require a slim filter, usually wide-angle ones, but this should be said in the specification. Also, if you stack filters, they may add up to too much.

In case it is the lens performance, try stopping down, vignetting generally becomes lower. Although this only applies to where the vignetting is pretty much symmetric. In the last example, there has to be something else wrong.

  • 1
    @unsignedzero - Burst, interesting. Could there be a problem with the shutter? Does the dark one use a different shutter-speed? Unless you were tracking the place and didn't notice an actual object obstructing your view. – Itai Oct 12 '15 at 1:33
  • Shutter would be less fuzzy than that, even at f/6.3. If it is anything internal it would just about have to be the mirror - except the α6000 has no mirror. And a mirror would be straight, not curved. Perhaps the internal IS moved far enough to place the bottom of the sensor (top of the inverted image) outside the light circle? – Michael C Oct 12 '15 at 18:29
  • The Sony a6000 lacks IS in the body or are you saying its from the lens itself? The lens IS is on for those shots. – unsignedzero Oct 15 '15 at 19:34
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When the image is mundane like cloudless blue sky, we see lots of defects not normally noticed.

Every lens projects a large circular image. The interior of the camera baffles and masks off the periphery leaving only the central image area. This is called the circle of good definition. Now every lens vignettes to some degree.

The cause of the vignette is called cosine error. Allow me to explain --- The lens handles every point in the vista as a point and projects that unique point onto the surface of film or chip. Now consider a flashlight’s focused beam hitting square on; you get a nice circular spot of light. Now aim the flashlight at the screen at an angle; you get an oval spot, not a circular spot. That oval has more surface area thus the same light energy must cover a greater area and thus the oval spot has less intensity. This is the stuff of the vignette. To date we can’t eliminate, on minimize. Mundane subject matter emphasizes the vignette.

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