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Why is there an artifact in top edge of my picture?

  • Camera: GH4
  • Lens: 20mm Lumix G 1.7
  • Shutter speed: 15 sec
  • ISO 100
  • f/16

Is this something in my sensor? There are two black dots visible under the shutter artifact, but could some litter cause this kind of "ghost shape"enter image description here

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    In the title you ask about the "bright spot" artifact, But then you ask about two black dots. What exactly do you want to know? Jan 17 at 11:13
  • The black specs are probably dust, likely on the back element of the lens if you don't see them all the time - this is shot at F/16 and dust on the back element gets sharper as you stop down. Dust on the sensor looks the same in every shot.
    – J...
    Jan 17 at 15:52

5 Answers 5

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This artifact falls under the heading of flare / ghost image. It is caused by internal reflections. The camera lens is a complex array of multiple polished glass lens elements. Some elements are cemented together, some are air-spaced. Each has two polished surfaces that reflect away about 2% of the light that otherwise would traverse the lens. The 2% that is reflected hits other polished surfaces and reflects. The bottom line is, there is a fair quantity of unwanted reflections going on inside the camera.

Most of this stray light bathes the film or sensor with a uniform level of stray light, and this reduces image contrast. What you are seeing is a ghost image of the iris (aperture). This is a common phenomenon caused when there is a bright light source just outside the edges of the image.

You could have likely mitigated this artifact if you had mounted a lens hood. This is a funnel-like attachment that mounts surrounding the front of your camera lens. The lens hood shields the lens from seeing bright sources that are just outside the camera’s field of view. You might consider buying one, they are not too expensive. If due to bright light sources within the vista, nothing works to mitigate.

In the past, such artifacts and ghost images were more evil. Glass lenses actually reflect away about 4% however, nowadays they have a coat or multiple coats of minerals that reduce reflections to about 2%.

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  • Thank you Alan for the answer! You are right, i didn't use lens hood. Forgot to mention that.
    – Okasii
    Jan 16 at 17:02
  • When the likely source of flare is inside the field of view, lens hoods are no help at all.
    – Michael C
    Jan 23 at 11:57
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Nothing to do with your sensor, these are reflections of some bright light on the individual lenses in you lens. My bet is parasite light from the lamp post under which you were when taking the picture (lens hoods are also useful at night).

The dark spots could be birds.

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  • Thank you for the answer! you are right, i didn't use the lens hood.
    – Okasii
    Jan 16 at 17:03
  • Lens hood do nothing for reducing flare or other reflections caused by bright light sources within the field of view.
    – Michael C
    Jan 23 at 11:58
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The bright polygon spot in the sky can be a small water droplet on the lens.

Or, more probably, on the filter if you used one - the spot size and shape implies some distance between the optical irregularity that creates the spot and the lens.

The spot has a symmetric interference pattern suggesting that the light source illuminating it is not too much on the side, so the lens hood would probably be of little help.

The dark spots can be created by non-transparent contamination at the same surface, but they are too dim to be sure.


interesting: the "beams" around the lamps (14 around each) and the polygon shape (7 sides) are probably created by the same 7 diaphragm edges. Are the edges in fact 7 in your setup?

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  • +1 for explaining the 7-sided nature of it, though it's probably more likely just a garden-variety lens flare. Jan 17 at 14:36
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I don't think this is flare, though flare can often look similar to this.

This looks more like a drop of moisture, perhaps a single melted snowflake, was on the front of the lens and refracted the bright light from the streetlamps in that way. Out of focus water drops on the front of a lens can often demonstrate the "onion skin" layers in an aperture shape.

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    I think this is the closest answer. A tiny water droplet on the front element is effectively a microlens, magnifying the entrance pupil and it's diffraction effects (the onion ring pattern).
    – scottbb
    Jan 17 at 20:34
  • A snowflake might explain the polygonal shape. A drop of moisture would have left a round spot.
    – FluidCode
    Jan 18 at 13:19
  • @FluidCode No, it would not have. Light is least focused at the front of the lens. The polygonal shape is that of the lens' aperture diaphragm.
    – Michael C
    Jan 18 at 21:05
  • Not to mention that snowflakes have a hexagonal shape, not a seven-sided shape.
    – Michael C
    Jan 23 at 11:59
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Do you mean the 7 sided polygon on the top? That's your aperture blades. What is the origin of the hexagonal artifact of direct sunlight/spotlight photos?

You're catching flare from the light, it is bouncing between lense elements, and eventually exiting in that orientation. You're at a very small f-stop with lot of integration time to pick up subtle flare.

Had you shifted the lense down or up you could probably push it out of the frame, although you may still have had an indistinct lightening / cast in the direction of the flare.

A lense hood may mitigate or eliminate the artifact if the light was outside of the lense FOV but, given the source is the light in your photograph, this artifact still would have shown up.

Edit: htps://www.opticallimits.com/olympus--four-thirds-lens-tests/464-pana_20_17

Number of aperture blades 7 (circular)

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