Why does a bright star or planet appear multiple times in my photo?

Asked 4/19/2021

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In a cropped night-sky photo, one bright object appears as several similar spots. The image was taken at ISO 3200, 3 seconds, with a Sony A57 and an 18-55mm f/3.5-5.6 SAM II lens. Is this caused by a low-quality camera/lens, internal reflections, or simply being out of focus?

Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0

Photography Stack Exchange contributor

5y ago

2 Answers

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The combination of color cast and differing brightness of the "ghost" images is telltale for internal reflections in a coated lens. It's not necessarily a sign of low quality optics or sensor, but it's characteristic of a bright light source in frame on a dark field -- making the reflections (typically 1% or less of the brightness of the main object, with coated lenses) more visible than they'd be with a field closer to the brightness of the primary object.

The random seeming arrangement, along with the inversion of at least one reflection, is due to the convex and concave curvatures of various elements. It's likely, also, that this effect is exacerbated by the presence of a filter in front of the lens (skylight or UV filters don't block much light or change image color noticeably, but they do offer at least two more surfaces to return reflections to the sensor).

Another possibility in this case is that you have multiple out of focus images of star-like objects. When out of focus, the image recorded tends to take the shape of the aperture in the lens or telescope -- with typical camera lenses, this will give a polygon with (almost always) an odd number of sides, but with some lenses, or when the aperture is wide open, you may see a circular or near-circular image, possibly with internal shading (like the brighter images above). You can't depend on the infinity stop in your lens to give correct focus for star images, and auto-focus systems may also fail in a field containing mostly darkness. Careful manual focusing on the brightest object available (Moon, Jupiter, Venus, etc.) is probably the best method of getting sharp point-like images.

Originally by user89902. Source · Licensed CC BY-SA 4.0

user89902

5y ago

0

AI Answer

Generated from our catalog & community — verify before relying on it.

It’s most likely not your camera being “low quality.” Based on the answers, there are two plausible causes:

  1. Out-of-focus bright points: A bright star or planet can appear as multiple soft blobs if focus is off. Their shapes may vary across the frame because lens rendering changes from center to edge.
  2. Internal reflections (ghosting): Bright lights against a dark background can also create faint colored ghost images inside the lens. This is more visible at night and can be made worse by a front UV/skylight filter.

From the community replies, the varying shapes suggest out-of-focus stars/planet is the stronger explanation, though some reflection/ghosting is also possible.

To reduce it, try:

  • Focusing carefully at infinity using magnified live view if available
  • Removing any front filter
  • Stopping down slightly if practical
  • Reframing so the brightest object isn’t near problematic parts of the frame

UniqueBot

AI

5y ago

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