Photography How To: Large Moon

Large half moon behind the Mitchell Library in Glasgow, Scotland

Moon behind the Mitchell Library

A large half moon behind the dome of the Mitchell Library in Glasgow, Scotland with both the moon and the building in focus and at the desired exposure.

This is a composite image created by digitally combining two photographs. Even had the moon been present in the scene, a single image to get this exposure of the building would have produced a much smaller moon that would have been overexposed showing none of the detail that is seen in this image.

For this type of shot you will need a telephoto lens, a tripod and suitable photo editing software (e.g. Photoshop or GIMP)

There are a number of methods by which this effect can be achieved. The moon was shot individually at 200mm,  the image then digitally enlarged 4x (2x on each side) and the sky digitally rendered black. An unsharp mask was applied to sharpen the moon and the image was cropped to the same dimensions as that of the building.

The cropped moon image was superimposed in a separate layer with the building as the background layer. The black colour was then set to alpha to render it transparent, leaving behind only the moon and revealing the image of the building, before merging the layers. The same result could also have been achieved by using HDR techniques.

The sky in the shot of the building was actually overcast though with no cloud texture. The blue colour cast, from using incandescent white balance, has rendered the appearance of a dark clear sky.

Camera Settings for the moon:

  • ISO 200
  • Aperture: F/16
  • Shutter speed: 1/6s
  • Focal length: 200mm
  • White balance:  cloudy
  • Shooting mode: manual
  • Release mode: remote mirror-up

Camera Settings for the building:

  • ISO 100
  • Aperture:F/16
  • Shutter speed: 10 seconds
  • Focal length 100mm
  • White Balance: incandescent
  • Shooting mode: manual
  • Release mode: remote mirror-up

The images were combined using GIMP 2.6. with the following steps:

  1.  Place the images to merge in a single folder
  2. Open GIMP then select File > Open as Layers and select both the images to open
  3. Ensure that the image you wish to leave unedited (the building in this case) is the background layer
  4. Select the foreground layer by clicking on it in the layers display (right panel in GIMP)
  5. From the main menu select Colors > Color to Alpha
  6. In the colour palette  select the colour you wish to render transparent (black in this case) and click OK
  7. From the main menu select Layer > Merge Down
  8. Click File > Save As to save your completed image – choosing a different file name so as not to overwrite your original image.
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