Photographing the Moon - StarLog 12/08/2014

Oklahoma has been foggy and overcast these past few weeks, but a few days ago there was a break in the weather and I was able to try out a new lens I got for my new digital single-lens reflex (DSLR) camera.  I was very happy with the image I was able to resolve and I learned something interesting when I decided to share the image with my friends and family.  What I learned was that most people cannot appreciate a good moon pic when they see one!  This is not to say that my photograph is a top-notch moon pic but I would like to explain how I took it to shed a little light on the effort needed to capture pictures of subjects that are 238,900 miles away from the sensor in your camera…

High resolution image of the moon shot on my Canon EOS Rebel T5i, EF 70-300 mm f/4-5.6 IS USM, f/11.0, 1/125 sec, ISO 200 in the parking lot outside my apartment on 12/8/14, 12:35:25 PM.

 

 

To wrap your head around how far away the moon is next time you find yourself outside under a full moon extend your arm to its full length and put your pinky finger in front off the moon.  Your pinky finger will cover almost exactly 1-degree of the night sky; the moon is about a half a degree across.  This shows that the moon is really actually very small; it only seems so big because everything else in the night sky is so much smaller.

The equipment that I used to capture the image include my Canon EOS Rebel T5i DSLR, EF 70-300 mm f/4-5.6 IS lens, a small tripod and an intervalometer as a remote shutter release.  Because of the distance and brightness of the moon I had to manually control the settings on the camera and lens to bring the moon into focus.  There is some skill in bringing a subject into focus in the cameras manual setting.  The three basic variables to the camera include aperture, shutter speed, and ISO.

Digital Single Lens Reflex (DSLR) Camera diagram. Source.

Aperture controls the amount of light that reaches the camera’s sensor.  It functions similar to the iris in our eyes by acting as a variable hole or window by which light can travel through.  If the aperture is narrow, then highly collimated (parallel rays of light) rays of light are focused on the cameras sensor resulting in a sharp image.  A wide aperture allows for light rays that are un-collimated to reach the sensor resulting in a less sharp image.  Aperture is measured as a series of f-stops that is the ratio of the focal length of the lens to the diameter of the aperture.  For example, if you’re using a 50mm lens and set the aperture to f/2, the diameter of the aperture will be 25mm.  In my case I was using a 300mm lens and used an f-stop of f/11.0 making the diameter of my aperture 27.27mm.   

Diagram of aperture by f-stop value. Source.

 

The shutter speed controls the amount of time the shutter will allow light to remain on the sensor.  This is measured in seconds and fractions of a second, or in the case of long exposures (required by most astrophotography) any amount of time so long as the camera is charged.  Because the moon acts as a mirror that reflects sunlight it is very bright and requires a fast shutter speed.  I used my benchmark as 1/1000 sec but cut it down to 1/125 sec for my image.  This short shutter speed is why the background is completely black, had I used a longer exposure some stars might have been able to accumulate in the image.

Diagram showing the effect of decreasing the shutter speed on a moving object.  Source.

   

ISO is the sensor sensitivity and determines the level of sensitivity of the camera to available light.  The lower the ISO number (ISO 100), the less sensitivity your camera will be to the light , this would be appropriate for a sunny day.  While a higher ISO number (ISO 3200) increases the sensitivity of your camera, this would be useful in low light conditions without the use of a flash.  In the case of my image I used a low ISO of 200 to reduce the graininess or “noise” that accompanies higher sensitivity.

Sectioned off image showing the effect of increasing sensor sensitivity.  Source.

 

So in summary I used a 300mm lens, with a narrow aperture of f/11.0, a fast shutter speed of 1/125 sec and a slow sensor sensitivity of ISO 200.  I was able to choose these settings because of a unique live view mode that my camera has built in.  This live view mode allows me to make certain adjustments to the camera and see a real time image of what the sensor will most likely reproduce.  In addition to this I manually focused the camera lens by zooming into the image and focusing the camera ring until the craters were crisp in the liquid crystal display (LCD) screen.  It was only then that I was able to tell the remote shutter to take the picture.  But I was not done yet.

I shot the picture using a camera raw image file that contains minimally processed data acquired from the camera’s image sensor.  This file has not yet been processed and allows for digital processing without adding to the original image.  All I did to my file was tweak the whites and blacks, shadows and contrast to really show the difference in surface features (lava fields = dark, regolith = light).  Then I slapped the file into Photoshop where I cropped the image to keep a high pixel density (prevent image blurring).  In the end the picture went from this:

The very over exposed image captured when using the cameras recommended settings.

 To this:

Image captured in manual mode before tweaking the raw file and cropping the image.

To a professional quality image:

An image that is not only visually stunning, but one that brings into focus another world.  The photograph resolves impact craters, lava fields, and even the very patch of land where man first walked on the moon!  It is really exciting how accessible high-level technology is becoming and with advances in optics and camera technology the sky is no longer the limit.