Introduction

Winter in The Netherlands. This shows one of the centuries-old windmills scattered throughout the country.

Double exposures are interesting for artistic purposes; since the moon is so much brighter than the landscape at night, you can never photograph both in one frame with proper exposure. It is a fun technique to try, but don't take it too seriously. You can, however, express all your creativity with double exposures.

In this document I will assume you try the technique at night, by full (or gibbous) moon.

Suitable camera

You will need a camera with a multi-exposure option. Not all cameras have this option. The Nikon FE cameras which I use now have a convenient lever for it, as probably do other newer SLR bodies. Maybe your camera will even have a program mode for it.

If you have an older SLR camera which does not have a multi-exposure option, there may be a way to trick it. I found a way to trick my old Praktica camera doing multi-exposures as follows:

• take a photo (the first frame of the series);
• retension the rewind lever, so that the film is tightly rolled, and hold on to it so it doesn't roll back;
• while holding the rewind lever, push in the winder-unlock pin (this is used to unlock the film winding cylinder when you want to rewind the film);
• While holding the rewind lever and pressing the rewind unlock pin simultaneously, wind the film as you normally would. However, you will notice that the film does not transport to the next frame, since you have the transport mechanism unlocked.

Now the shutter is ready for taking a picture over the first picture. You can repeat this as many times as you want.

Note: it is a last-resort method for making double exposures, and sometimes (if you don't have the rewind lever tensioned all the way) the film will still transport a bit, or even rewind a bit if you have the lever tensioned too much. Hence, you may end up with shifted frames. But it works, if you don't have another solution.

Lenses

Typically, you will make a double exposure (as opposed to multi-exposure of several more frames). The two exposures differ greatly in exposure times (shutter speeds), due to the difference in magnitude of the moon and the landscape.

If you want a real big moon, you have to use a lens somewhere in the range from 500mm to 1000mm. Aperture should not be a higher number than f/11 (or the moon will be blurred due to Earth's rotation). For the landscape, any lens will do, depending on your frame composition.

Equipment

Apart from the obvious equipment, use a tripod and cable release for both the moon and landscape exposure. Use a sturdy tripod, especially if you will use a very long focal length telephoto lens for the moon, such as a 500mm or 1000mm. With longer exposures (longer than 1/100 sec) with such a lens, the photo may be blurred already by just the tremor of the SLR camera, when it flips the mirror upward. When I photograph with the 1000mm lens or longer, I use an old army-surplus tripod made by wood, used for theodolites, and modified for fitting a tripod ball-head on it.

Snowscapes do well with this technique. These photos sell well as Christmas wishing cards.

Exposure

Typically, you will need exposure times for the landscape at between 1 and 4 minutes, f/2.8, using 100 ISO film. The exposure times for this differ so widely that I can't possibly give a correct value; it depends a.o. on lunar altitude, cloudiness, light pollution, lunar phase, time of year and day (night), albedo of landscape, etc. So, use your camera's exposure meter, and expose 1/2 to 1 stop longer than indicated to account for the film reciprocity error. Make sure you also bracket your exposures (one stop less and another with one stop more, to experiment).

It is better to choose a higher aperture such as f/5.6 and f/8 combined with a longer exposure time, so your photo will be sharper and show less vignetting.

For the moon, the exposure differs too, and this is even more difficult to determine because of the various phases of the moon. The brightness of the moon is not just the percentage of disk illuminated! Due to the dry-heiligenschein effect and retro-reflective minerals on the lunar surface, the full moon is much more bright than one would think based on phase angle. So, I'm giving you a formula to determine the proper exposure to within 1/2 stop or so. This formula worked well for me.

t = F² / (K * ISO)

where:

• t is the shutter speed in seconds
• K is a constant:

  20	for crescent moon
  40	for first/last quarter moon
  100	for gibbous moon
  200	for full moon

• F is the focal ratio (e.g. F=16 for f/16)
• ISO is your film speed, e.g. 100.

So, say you are using a 1000mm lens on f/11 with 100 speed film for the moon, and the moon is gibbous. Then t = 11² / (100*100) or t = 121/10000 sec, or about 1/80 sec.

Tips

There are a few things that will make your pictures look more realistic (or less unrealistic, if you will):

• First of all, make sure that any shadowing in the picture is not too well visible, because you will in general have the moon at a completely different place in the sky on your frame than it was. So, try to have the shadows of structures (if at all visible on your photo) coming towards you, which would be more logical with the moon being in view.

• Also, if the moon is high in the sky, photograph the moon at an angle, depending on which direction you will make the landscape photo. If the moon were low in the sky as the photo will suggest, the lunar structures (maria and craters) would appear to be rotated. This is especially important when you photograph a crescent moon, which will never show vertical if it is just above the horizon (the light crescent should always face more or less downward, with the horns facing upward).

  Don't make your photos look too unrealistic - i.e. don't have the moon too big on the photo when it doesn't match with the composition.

• The most important thing to take into account is the position of the moon in your frame. Make sure that you remember well exactly where the moon would be located in the frame, when you do the landscape exposure, so that no structures end up in front of the moon. If that happens, the moon will appear to be in front of the structure. If there are clouds in the sky, that will make it even more complicated, but if the clouds are not too thick (like cirrus), generally it will still look realistic (it may even look beautiful).

• You can also create stunning photos with a lunar eclipse, this way. But then the exposure time for the moon would be much longer.