[Lunar Photography]

by Michael Oates

[ Lenses ] [ Teleconverters ] [ Cameras ] [ Mounting ] [ Film ] [ Exposure ] [ Method ] [Tips ] [Examples ] [Lunar Eclipses ]

Introduction

This article has been produced based on my practical experiences when taking photographs of the moon.

These techniques work well for me, but I have no doubt that there are other ways of getting good results, so if you find a way of taking astrophoto's that you are pleased with, then stick with them and enjoy. Don't go mad and buy the most expensive equipment make the most of what you have, you can often find less expensive equipment producing very good quality work, it's how you use it that matters.

I shall be referring to astrophotography using camera lenses only, but a lot of the techniques are applicable to astrophotography through a telescope as well.


Lenses

One big mistake beginers make when trying to photograph the moon is using a camera with too short a focal length lens. Although the moon to the naked eye may seem quite large, with quite a bit of detail seen. When photographed the resulting image is far to small and looks like a small dot on the print or slide, with no or little detail recorded.

In order to demonstrate how large (or small) the moon appears on a 35mm film I have taken a number of photographs of the Moon with different lenses ranging from a wide angle lens of 24mm focal length right up to an 1600 focal length telephoto (an 800mm lens with a 2x teleconverter).

[24mm] [50mm] [135mm]
[300mm] [800mm] [1600mm]

As you can see you really need a focal length of 800mm or over the best being 1600mm which allows the moon to fit in the frame easily. The following table shows the size of the moons image on 35mm film when taken with various focal length lenses.
You can use the following calculation to determine the image size on 35mm

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Teleconverters

It is often said that teleconverters degrade the image and should be avoided, and that they also loose a lot of light, typicaly 2 stops for a 2x converter.

What I have found by experience is...

"An image produced with a teleconverter is FAR SUPERIOR to an image taken with the same lens without the converter and having the image enlarged to the same scale."

Why ? Well it's down to the resolving power of the film, if you enlarge a negative or transparency you enlarge the grain, and the amount that the teleconverter degrades the image is less than you loose by enlarging the film. And you have the added advantage of having a larger image on your slide in the first place. I can not say this of 3x converters as I have only used 2x and I would certainly recomend only using good quality multi-element converters that have all the optical surfaces coated.

You need not stop at one teleconverter, I regularly use two 2x converters together and the results are fantastic, far better than enlarging the image afterwards.

As to the light loss, well, were talking about photographing the 2nd brightest object in the sky, (the brightest being the Sun) so we can aford to sacrifice a bit in order to get better images.

I would like to add that a 1000mm lens is likely to produce better images than a 500mm with a 2x converter, so if you have a choice use the longer lens.

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Cameras

Most of my photographs of the moon were taken with a Practica MTL5B, a 35mm SLR (Single Lens Reflex) manual camera that takes low cost 42mm thread lenses. The camera was also very low cost. One criteria that I believe is important with a camera is that when the shutter is pressed very little vibration occurs when the mirror is moved out of the way to take the picture, or when the shutter opens. Any vibration from the mirror or shutter will cause the image to blur, this being more pronounced the longer the focal length of the lens. There are ways of stopping the vibration caused by the mirror, one is locking the mirror out of the way before exposure. But this has its drawbacks as you can't see the moon in the viewfinder just before the exposure, which could mean the moons image may be off centre or even off the image altogether. Another method uses a sheet of black card, see Tips.

An automatic camera is not required, indeed it could be undesirable as under exposure could occur if the light sensor of the camera is in the centre of the image, where the bright moon will cause the camera to either stop down the lens of or reduce the exposure time. The opposite may occur if the sensors pick up more of the background. Also automatic camera's tend not to work so well in sub-zero temperatures that we astrophographers tend to use our cameras in. Better to use a manual camera or if you must an automatic one that has a manual over-ride. The best type of camera should have a mechanical shutter and not an electronic shutter, due to problems at cold temperatures.

I will deal with how to calculate the exposure later.

The camera must have a cable shutter release. This is used to reduce any vibrations that may be caused by operating the shutter.

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Mounting

For most lunar photography if you are not using very long local length lenses or if the exposure is shorter than about 1/2 sec then a sturdy tripod is all that's needed. But for long local lengths and longer exposures then a driven mount will be required. This can be a small mount that fits on a camera tripod

Mount Motorised camera drive.

Or if you have the equipment a larger equatorial mounting.

I can't emphasise enough the necessity of a good strong tripod that does not vibrate like a tuning folk every time the shutter is pressed. If you can't keep the camera still during an exposure you will be very disappointed in the results.

The camera mount shown in the photo above is powered by a battery and only requires very approximate polar aligning to give good results. The polar aligning tube can be seen on the left. This type of drive has the advantage of being very portable. The lens used above is a 800mm FL f8 Tokina telephoto lens. It is unusual for such a long focal length not to be a mirror lens. (it does make it a little long to handle at times)

longlens
Photo of 800mm telephoto lens and Zenit camera on a fixed tripod. Ignore the Mylar covering the lens, it was set up to photograph the Sun.

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Film

As the Moon is a bright object, slow fine grain films can be used, indeed best results will be made with the slowest of the films...

Both these are 25 ISO rated films and are capable of producing very sharp well defined images.

As you move to faster films, the film grain starts to degrade the image. There are times when faster films are an advantage, when faster shutter speeds are needed, if a motorised camera mount is not available or when photographing a lunar eclipse, when much longer exposures are needed.

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Exposure

The easiest way of calculating the exposure is to use the Exposure Calculator available on this server. With this calculator the exposure can be determined for any speed of film and lunar phase. When using the calculator, until you are proficient in lunar photography, you should bracket the exposures, i.e. you should take 3 exposures, one over exposed by 1 or 2 stops, one exposure as indicated and another under exposed by one or two stops.

In table below the exposure can be determined for 25 ISO film.


        	Lunar Phase (Exposure Times in Seconds)

f		Thin	 Wide	Quarter	Gibbous	Full
      	      Crescent Crescent  	

1.4		1/125	1/250	1/500	1/1000	-
2		1/60	1/125	1/250	1/500	1/2000
2.8		1/30	1/60	1/125	1/250	1/1000
4		1/15	1/30	1/60	1/125	1/500
5.6		1/8	1/15	1/30	1/60	1/250
8		1/4	1/8	1/15	1/30	1/125
11		1/2	1/4	1/8	1/15	1/60
16		1	1/2	1/4	1/8	1/30
22		2	1	1/2	1/4	1/15
32		5	2	1	1/2	1/8
45		15	5	2	1	1/4
64		45	15	5	2	1/2
90		-	45	15	5	1
128		-	-	45	15	2
250		-	-	-	45	5

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Method

I will describe 3 different methods of actualy taking lunar photographs, choose the one that best matches your situation.

Long focal length lens on camera drive

I will assume for this example that the lens used is an 800mm f8, Film used 25 ISO, and the Moon is at quarter phase.

Roughly polar align the camera mount, and get the moons disk in the centre of the view finder, if the motor drive is switched on, it will keep the moon in the centre of the view finder for quite a while.

Focus the image and set the exposure on the camera, (in this case I am assuming an exposure of 1 sec at f32), which was obtained from the Exposure Calculator.

When you are ready to take an exposure, hold a piece of black card in front of the lens, making sure you don't touch the lens. press the shutter using a cable release, then wait a few seconds for the vibrations to die down then quickly move away the card and replace it again 1 second later with the card still in front of the lens, close the shutter. I would recommend repeating the same exposure a few times in the hope that one is sharp. You should also take more exposures at different exposure times, just to make sure that the correct exposure has been given.

Long focal length lens on fixed tripod

With this set-up you have to make a choice as to whether you use a fast film so that the shutter speed can be high, or use a slower film and use the black card technique as above but you will be limited to less than 1 second, preferably less than 1/2 sec, as the moon will move to much causing the image to blur.

Short focal length lens on fixed tripod

If shorter focal length lenses are used any movement of the moon in the short exposures will not degrade the image as there will be little detail recorded anyway. Also the use of black card for the exposure may also not be required, (it will have to be determined by experiment). To record as much detail as possible of the lunar features a fine grain film should be used, otherwise any detail will be lost in the grain.

If longer exposures of up to 20 - 30 seconds are taken with standard lenses, using faster film (400 ISO or highter), and wide apertures, you will record some of the brighter stars and planets (if they are in the same area of the sky). These photo's can be very pleasing. Many people try to photograph as many solar system bodies as possible in one frame. Note the Moon will be over exposed.

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Tips

Don't be afraid of taking many photographs in one session. Shoot a whole roll of film if you can afford to do so, just in order to get one or two good shots on film. There are a grest many obsticles in our way of getting that perfectly sharp image.

To stop mirror and shutter vibrations from blurring the image. Hold a piece of black card in front of the lens, making sure you don't touch the lens, press the shutter using a cable release, then wait a few seconds for the vibrations to die down then quickly move away the card and replace it again after the exposure time has elapsed, with the card still in front of the lens, close the shutter.

Use a Lens hood to stop stray light from street lights etc striking the lens causing loss of contrast and internal reflections producing flares on the image. It will also go a long way in preventing the lens from dewing up.

Unless you can process and print your own photographs, use slide film. You will be very lucky if you can find a commertial photolab to make good prints of astronomical images, even images of the moon.

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Examples


Lunar Eclipses

Taking photographs of lunar eclipses requires a few different techniques. The Moon normally is a very bright object, but during a total eclipse the Earth comes between the Moon and Sun, with the Earth casting a shadow on the full Moon. This makes the Moon a very dark object, so with less light available exposures need to be longer and faster films may also be needed.

The actual brightness of the Moon during an eclipse varies a great deal, not only during the eclipse but each eclipse can be very different from each other. Variations in the weather and the amount of dust in the atmosphere, can cause the Moon to almost disappear from view.

So to give precise exposures for an eclipse is not possible, only a general guideline. You should then bracket your exposure widely to ensure you get some well exposed pictures.

The Moon does not suddenly disappear during an eclipse, it first enters a penumbral phase where the Moons disk is only partially shaded, this moves across the disk followed by the umbral shadow. depending on your exposure you can vary the look of the Moon greatly from what you can see naked eye.

In order to try and capture on film the advancing edge of the shadow, you might need to under expose slightly, over exposing will just burn out the image, and the shadow may not be seen.

As longer exposures are needed you may need to drive the camera, to keep the Moon sharp. Alternatively you can use a shorter focal length lens, but by doing so the image will be much smaller.

Faster films will help you keep the exposure length down, but the faster the film the more obtrusive the grain size will be.

Colour film is the better then B&W with this subject, due to the lovely reddish colour the Moon takes on during totality.

You may also be able to record stars very close to the Moon, which is something that's not normally possible due to the normal brightness of the Moon.

Not all eclipses are total, many are partial, where the Earth shadow does not completely cover the lunar surface. There are also penumbral eclipses where the Moon only ever enters the penumbra of the shadow. It can be quite a challenge to get a good image of a penumbral eclipse due to the lack of any clearly defined shadow. The difference in brightness from the penumbral being very slight.

A good starting point for exposure when photographing the penumbra is...


Hope these notes are of some help.

Michael Oates

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Maintained by Michael Oates
Page modified 22 January, 2005