MOONSHOTS - How to take photographs of the moon

By Bob Taylor

For many photographers the moon is an interesing subject to photograph, which often proves difficult to capture. This article explains why, and shows how to get good Moon images.

The angular diameter of the moon in the sky is only about 0.5°, so unless a long telephoto lens is used, it will fill a very small part of the frame, even with a high megapixel camera the number of pixels that will cover the diameter of the moon will be quite low. A full moon when the moon is near to its closest position on its orbit is called a Supermoon. The moon photograph above was the Supermoon taken on the 27th April 2021, the next one will be very slightly larger on the 26th May 2021.

The graph on the next page is used to see how large the moon - measured in pixels to cover its diameter will appear on a digital image, using different lenses and sensors. It also indicates the average, minimum, and maximum size due to its orbital posi�on.

To use the graph, find the actual focal length of the lens (NOT the 35mm equivalent) on the X axis, and follow the line up to the coloured lines that corresponds to the pixel size of your camera’s sensor. Where they cross, the number of pixels that will cover the diameter of the moon is found on the Y axis. As an example, a 300mm lens and a 5µm sensor will give an image of an average moon of about 540 pixels in diameter. Pixel sizes that fall between the lines on the graph are inversely propor�onal to the change in pixel size, e.g. a sensor with 4.4µm gives 10% fewer pixels than are shown on the 4µm sensor lines.

The moon reflects about 12% to 13%. of the light that hits its surface, so it is actually somewhat darker than the 18% grey that is used for photographic grey cards used to set ‘correct’ photographic exposure. From Earth, the part of the moon that we can see, is lit by sunshine that is brighter than the brightest sunshine seen on Earth. The light reflected from the moon sca�ers as it passes through our atmosphere, when near the horizon, it appears to be more red/orange as these colours are sca�ered less by the atmosphere, and it gets whiter as it rises in the sky, with the moonlight passing through less atmosphere. Unless you are using a long telephoto lens and spot metering, at night, most camera exposure systems will overexpose the moon as the metering system will be exposing mainly for the dark background. Since we know that on a clear night the sun is shining brightly on the moon, it is easiest to switch to manual exposure mode, using an exposure of 1/250th second at f8 @ ISO 100 or equivalent, and autofocusing, will deliver an image that is good for further processing (digital or nega�ve film). The histogram of the cropped full moon image shows that the moon does not include the lightest and darkest tones, this is because it is a low contrast subject. To produce an image with good contrast and detail - using “levels adjustment” produces about 60 levels of brightness from a jpg image with significant gaps in between the levels. The same image recorded as a 14 bit RAW file - a�er adjus�ng the levels produces about 3,800 levels of brightness with no discernible gaps between the levels. The RAW image thus provides much more poten�al for further post processing.

Many of the more impressive photographs of the Moon and landscapes are actually produced by superimposing two images, one exposed for the Moon and the second exposed for the landscape.

A current trend is photographs of the moon posi�oned exactly at a key posi�on, such as just above, or framed by a geological or architectural feature. PhotoPills is a smartphone app (€10.99) that predicts the posi�on of the moon (or sun or Milky Way) based upon the �me, and the posi�on of the feature, and guides the photographer to be at the exact posi�on at the right �me to capture the planned image.

©Bob Taylor