How Large is the Moon in a Photograph?

Sunday, 29th July, 2018

During the early morning of Saturday, 28 July, 2018, a special celestial event was to occur: a total lunar eclipse, resulting in a red moon - one like this:

Red Moon

Red Moon

I captured this particular red moon on 28 August, 2007.  Incidentally, it was the first and last red moon I captured!

For the most recent total lunar eclipse, I planned to rise early and capture the moon.

Unfortunately, due to cloud, I barely caught a glimpse of it, so no images were forthcoming.

The night before, however, I captured some images of the rising full moon in the early evening.

Now, there are different ways of photographing the moon.

Some people like to place the moon in the context of a broader scene, depicting trees, city architecture, animals or people.

Other people like to capture the moon in and of itself, with a view to depicting as much detail as possible.

I have historically fitted into the latter category, and I have photographed the moon numerous times with it being the only subject.

Naturally, when using only DSLR equipment and no telescopes or other space observation equipment, I like to use the longest focal length possible so that the moon in all its glory is more prominent, and therefore larger in dimension.

The maximum focal length I can achieve is 1,120mm by attaching both a 2x tele-converter and a 1.4x tele-converter to my 400mm lens.

People often wonder which focal lengths to use for capturing the moon.

Which focal length to use depends on the kind of image desired.  In my case, I want as long a focal length as possible.

Once a focal length has been decided, the next question is as follows:

How large will the moon appear in my image?

The answer is that it depends on several factors; namely:

  1. the focal length;
  2. whether the camera is a full-frame, APS-C or APS-H model (the latter two of which crop the view a full-frame lens natively provides on a full-frame camera); and
  3. the distance between the moon and the earth.

The short answer is that the moon is not very large relative to the frame.

If an APS-C camera is used, there is a distinct advantage, as the moon will appear larger relative to the frame than it would when captured with a full-frame camera.

In my case, I have only full-frame DSLR cameras.

Today I decided to explore and compare the size of the moon relative to my camera's frame size, when shot at different focal lengths.

The night before the total lunar eclipse, I went outside to capture some test images.  I happened to capture images at both 1,120mm and 800mm.

Both focal lengths are considered extreme super-telephoto focal lengths in the DSLR world, but there is a surprising difference between them.

In both cases, the moon is not very large, relative to the frame.

I use a Canon EOS 5D Mark IV, which produces a native image size of 6,720 x 4,480px (30,105,600px).

Let us take a look at how many times the moon can fit into that frame size when captured at the two focal lengths I used.

This is an image measuring 6,720 x 4,480px (the exact image dimensions a Canon EOS 5D Mark IV produces), depicting the size of a full moon relative to the size of the frame.

Moon Captured with Canon EOS 5D Mark IV at 1,120mm

Moon Captured with Canon EOS 5D Mark IV at 1,120mm

The full moon was captured in Sydney on 27 July, 2018 at 17:50, using a focal length of 1,120mm.

The moon, when captured at 1,120mm at this particular time, measures approximately 1,751 x 1,741px (3,048,491px).

With a frame size of 6,720 x 4,480px (30,105,600px), this means that the moon occupies approximately 10.1% of the frame.

Equipment used:

This is an image measuring 6,720 x 4,480px (the exact image dimensions a Canon EOS 5D Mark IV produces), depicting the size of a full moon relative to the size of the frame.

Moon Captured with Canon EOS 5D Mark IV at 800mm

Moon Captured with Canon EOS 5D Mark IV at 800mm

The full moon was captured in Sydney on 27/07/2018 at 17:54:19, using a focal length of 800mm.

The moon, when captured at 800mm at this particular time, measures approximately 1,267 x 1,258px (1,593,886px).

With a frame size of 6,720 x 4,480px (30,105,600px), this means that the moon occupies approximately 5.3% of the frame.

Equipment used:

As can be seen, despite using long focal lengths on a full-frame DSLR, the moon is still relatively small within the frame.

Here are those key figures again:

In this case, the size of the moon nearly doubled with the use of a longer focal length, despite that focal length not being twice the size of the shorter focal length.

It is not quite an exact science, particularly when considering that the image shot with the 800mm focal length was captured just over four minutes later, by which time the moon had risen marginally higher; but it is a substantial difference.

In both cases, while the moon does not dominate the frame, it is certainly large enough to show very pleasing details.

Photographers desiring even more prominence and detail would be likely to attach the camera to a telescope, but if, like myself, a photographer does not have a telescope, but does have long focal lengths, a very pleasing result is certainly possible.