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Common Image Problems

Identify any problems with your images and find out what to do about them below.


Answer the questions above to help you identify your image problem. Click the back button to return to the previous question, or click the restart button to begin the questions again.

optics icon

OPTICS

Optical issues resulting in patches, ghost images, and bright pixels.

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 Are there stars in your image that shouldn't be there?
Description

There are remnants of over-exposed bright objects from the previous image in your image. This is called a ghost image. Ghost images can be identified by their non-stellar profile.

Example(s)

The two encircled objects are ghost images from overexposed bright stars in the previous image:

ghost-image

This is an example on a 0.4m SBIG camera.
Explanation

A bright star was over-exposed and left residual charge on the camera chip (CCD). This fades when the camera is read-out.
Next step

Re-take the image.
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 Does your image have dark rings or patches on it?
Description

There are dark rings or patches visible on your image.

 Example(s)

Archive links: NGC6654 , IC4603

rings-example

The example shown above is of NGC6654, taken by a 0.4m telescope.
Explanation

This is due to a bad flat field. Contaminants (e.g. dust, oil) from the telescope's optics can be seen in the image.
Next step

Send link to the data to science support.
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 Are there bright pixels in your image?
Description

There are bright pixels / groups of bright pixels in your image that shouldn’t be there.

 Example(s)

Archive links: NGC6872 , NGC5812 , M84

cosmic-rays

The example shown above is of NGC6872, taken by a 0.4m telescope. Some of the cosmic ray hits have been circled in green.
Explanation

These are from cosmic ray hitting the camera. Any image is susceptible to these natural phenomena, but longer exposures gather more of them.
Next step

These can be removed from data files by image processing tools such as AstroScrappy.
focus icon

TRACKING & FOCUS

Issues resulting in trailed stars and ring shaped stars.

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 Is your image out of focus?
Description

If the stars in your image appear fat, or they have a doughnut/ring shape to them, then your image is out of focus.

 Example(s)

Archive links: NGC6025 , NGC2467 , M3

out-of-focus

The example shown above is a section of an image of NGC6025, taken by a 0.4m telescope.
Explanation

The image is out of focus due to a focussing issue with the telescope. This can happen occasionally.
Next step

Send link to the data to science support.
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 Are the stars in your image comet-like in shape?
Description

Stars appear to look like “diamond rings” instead of doughnuts. They are comet-like in shape rather than round.

 Example(s)

coma

This is an example on a 0.4m SBIG camera.
Explanation

This is coma due to poor collimation.
Next step

Send archive link to science-support@lco.global.
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 Do the stars in your image look like ellipse-like rings?
Description

Does your image show ellipse-like doughnut shapes for stars?

 Example(s)

astigmatism

This is an example on a 0.4m SBIG camera.
Explanation

This is due to astigmatism.
Next step

Send archive link to science-support@lco.global.
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 Do the stars in your image appear to be stretched?
Description

Do the stars in your image look stretched into oval or rectangular shapes, instead of being circular?

 Example(s)

Archive links: M5 , HCG16

tracking

The example shown above is a section of an image of M5, taken by a 0.4m telescope.
Explanation

This is caused by some telescope movement during the observation.
Next step

Re-take the image.
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 Do the stars in your image appear fat?
Description

If the stars in your image appear fat, and they aren't ring shaped, then your image may have suffered from bad seeing.

 Example(s)

Archive link: NGC3953

bad-seeing

The example shown above is an image of NGC3953, taken by a 0.4m telescope.
Explanation

The problem is due to bad seeing. This can happen when there is turbulence in the atmosphere (non optimal observing conditions).
Next step

Re-take the image.
shutter icon

MECHANICAL PROBLEMS

Shutter problems resulting in faulty images.

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 Is half of your image dark with fewer visible stars?
Description

Is about half of your image dark with fewer stars, and the other half light with many more stars visible?

 Example(s)

Archive links: Hercules

hercules

The example above is an image of the Hercules globular cluster, taken by a 1m telescope.
Explanation

This is caused by the camera shutter getting stuck and being partially closed during the taking of the image, resulting in less light being captured for part of the image.

Next step

Re-take the image.
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 Are there upward trails from some of the stars in your image?
Description

There are distinct trails going upwards (+y direction) from the stars in your image.

 Example(s)

early-read-out

This is an example on a 2m Spectral camera.
Explanation

This is caused by the camera beginning the read-out before the shutter has closed.
Next step

Send archive link to science-support@lco.global.
camera icon

CAMERA ISSUES

Camera issues resulting in striped or patterned images.

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 Are there strange patterns across your image?
Description

There is a pattern across the whole of the image.

 Example(s)

electrical-pattern-noise

This is an example on a 1m Sinistro camera.
Explanation

This is electrical pattern noise.
Next step

Send archive link to science-support@lco.global. It is likely the camera will need to be taken offline.
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 Are there obvious stripes across your image?
Description

There are noticeable stripes going across the whole of the image.

 Example(s)

faulty-controller

This is an example on a 1m Sinistro camera.
Explanation

This is caused by a faulty controller on the camera.
Next step

Send archive link to science-support@lco.global. It is likely the camera will need to be taken offline.
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 Is there large-scale structure in your image?
Description

There is large-scale structure in the image (e.g. varied brightness pattern across image).

 Example(s)

Archive links: 29P

warm-CCD

This is an example on a 1m Sinistro camera.
Explanation

This is due to a warm CCD.
Next step

Send archive link to science-support@lco.global. ?
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 Does your image only show stripes?
Description

The image only shows stripes and not the night sky.

 Example(s)

unknown-camera-issue

This is an example on a 0.4m SBIG camera.
Explanation

This is an unknown camera issue.
Next step

Send archive link to science-support@lco.global.
other icon

OTHER

Other problems resulting in bad images.

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 Is there a gradient across your image?
Description

There is a gradient if the background colour/brightness changes across your image.

 Example(s)

Archive links: NGC7013 , NGC5806

gradient

The example shown above is of NGC7013, taken by a 0.4m telescope.
Explanation

The object is too close to the full moon. The brightness of the light from the moon creates an uneven light/colour gradient from one end of the image to the other.
Next step

Re-take the image.
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 Is the object in your image too small to see?
Description

If you find it difficult to locate your object or tell it apart from the other background and foreground stars in the image, then the object in your image is too small to see properly.

 Example(s)

Archive links: IC1747 , NGC6572 , NGC6765

too-small

The example shown above is of the planetary nebula IC1747 , taken by a 0.4m telescope.
Explanation

The object is too small to be taken by the 0.4 m telescopes. This is because the Field of View of the telescope is too large, so takes too large a picture of the sky to be able to see this object clearly. We’d need to use a bigger telescope, with a smaller Field of View (sees a smaller patch of sky but in more detail) to be able to see this object closer up.
Next step

Re-take the image using a larger telescope.
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 Is your image coloured incorrectly?
Description

Your image may be coloured incorrectly if there appears to be a coloured tint across the whole image. For example, your image, including the dark background, may have a red tint.

 Example(s)

Archive links: M99 , NGC2403

bad-colour

The example shown above is of M99, taken by a 0.4m telescope.
Explanation

This is caused by some cloud passing over the telescope during observation using a particular colour filter. This skews the colour of the image.

Next step

Re-take the image.
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 Is it too dark in your image to see your object?
Description

Is the object in your image too faint to see well against the dark background?

 Example(s)

Archive links: Pal 4

too-dark

The example shown above is of globular cluster Pal 4, taken by a 0.4m telescope.
Explanation

This is due to the exposure time being too short for an object with low inherent brightness. This can also happen with once bright solar system objects (e.g. comets) when they have moved too far away from the Sun in their orbit.

Next step

Re-take the image with a longer exposure time.
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 Does your image have a circular bright patch?
Description

Your image shows a bright patch which is circular in shape.

 Example(s)
Explanation

This is caused by the presence of a bright star just outside of your image.

Next step

Re-take the image.
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