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(Above) My own bridge camera - the Fujifilm S6500FD. Image credit: dpreview.com
The sky literally was on fire! Vertical fountains of intense green and white rays and shimmering curtains surrounded me as I stood at the centre of the field getting buffeted by the chilly Autumn wind which howled through the trees. Despite the inky darkness of the clear moonless night there was barely a star to be seen, even the fiery beacon of Mars was reduced to insignificance in the south, which it seemed was the only place under the entire dome of the sky which was left untouched by the frantic geomagnetic storm now assaulting the Earth’s magnetic field. The disturbance seemed to reach a crescendo as the zenith became masked in a bright crimson flame which flickered with an indescribable beauty like a silent explosion. This corona gave a final defying pulse of energy then faded into the background sky where one by one the stars returned. It was October 2003 and I had just witnessed one of the most amazing aurora borealis displays I had ever seen in my life. It was a visual experience like no other and impossible to describe its beauty with words. If only I had some way of recording the display, wouldn’t it be great I thought, if I could somehow show this to others. It was then that I decided that some day in the future I would get a digital camera and never again would nature’s most amazing performances be locked away in the depths of my mind.
Thousands of images later and now on my fourth camera, I’m still as passionate as ever about catching the best transient displays in the night sky. Choosing a digital camera in today’s high tech consumer marketplace is no easy feat and with a multitude of manufactures offering their latest image stabilizing lenses and computer packed bodies the beginner is more than likely to feel intimated or even discouraged. Sometimes the decision is made easier for us because of a strict budget. It was this latter factor which made me choose a bridge camera.
A bridge camera is so named because it “bridges the gap” between point and shoot pocket cameras and high end Digital Single Lens Reflex (DSLR) cameras. They look exactly like a DSLR with the exception that one cannot interchange lenses like their more expensive cousins. Despite this optical handicap they make up for it in other ways by providing the user with full manual control over all of the camera’s functions. It is this control, combined with a relatively cheap price tag, which makes these cameras very attractive to beginning astrophotographers. Not much as been written on the subject of bridge cameras however in my opinion they offer the budding photographer the perfect stepping stone into the amazing world of creative imaging. So, if you are more than familiar with a “point and shoot” and have moved on to a bridge camera and are wondering how to make sense of those fancy buttons then this article is for you. Here we will address a few simple concepts that will allow you to go outside after dark and take your first images of the night sky, and with a little practice and imagination it may even become your life long passion.
Getting Acquainted
Put your camera down, take out the manufactures instruction booklet, and read it from cover to cover. So many people neglect to do this and end up wondering why their camera takes poor images. You need to understand your camera to the extent that you can identify all the basic functions and how to access them. These can be found via buttons on the body, the menu on the LCD screen, and the rotating dial on top. Get intimate with these controls during the day time until you are competent with where they are located. Now, using the menu click through the settings and select “spot metering”. Find out how to select manual focus and never change it. On the rotating dial is a selection of symbols, ignoring auto mode and most of the others we are going to select several of these as our main tools for night sky photography. The symbols may vary from one camera model to the next but for the sake of simplicity I will use the examples on my own bridge camera which is a Fujifilm S6500FD.
Shutter Priority (S or SP)
Think of the shutter as the eye of the camera. Using this mode you can control how long that eye stays open. This shutter speed is measured in seconds and can be controlled via the up and down cross-buttons on your key pad. This value will appear as a positive or negative number allowing you to select any speed between 4000/second and 30 seconds. A value of less than one second is said to be a “fast shutter” and more than one second a “slow shutter”. For imaging faint stars we want to select the slowest speed available, in this case 30 seconds. This means that the “eye” is open for 30 seconds and will collect photons of light during that entire time. This will pick up stars fainter than can be seen with the naked eye. For this to be effective you must have your camera mounted on a sturdy tripod to get a crisp image. Use your camera’s 2 second or 10 second timer to avoid camera shake and vibrations.
Aperture Priority (A or AP)
We have already addressed how to control the duration the camera’s eye stays open (shutter speed) but now we are going to control the size of that eye or “Aperture”. Think of AP as you’re own eyelid. If you glance in the direction of the Sun you naturally close your eyelids to reduce the amount of light entering your eye. Similarly in a dark night your eyelids are wide open to collect as much light as possible to develop full dark adaption. With AP we are doing exactly the same thing. Using the cross keys again you will see that things look a little more complicated because the letter “f” is present in front of a series of numbers. Don’t be intimated by this, it simply stands for “focal ratio”. It’s easier to pretend it isn’t there. Instead look at the numbers, depending on your camera they might run from f/2.8 to f/8 with various increments in between. A small number means the eyelid is wide open and a higher number means the eyelid is narrower. For astronomical work we want to collect as much light as possible and so keeping the eyelid wide open so we will select the lowest possible “f” number. When we do this we say the lens is “wide open”.
ISO (Sensitivity)
Activated through your camera’s LCD menu or the round “f” button nearby, this is perhaps the second most important setting after shutter speed. ISO will range from 100 to 1600 or more and is simply a measure of the sensitivity of your camera, so the higher the number the more sensitive it will be. Daylight photography is typically carried out at ISO 100; however night sky photography requires a lot more sensitivity so I would suggest a value between 400 and 800 for most subjects. A higher value can be selected but keep in mind that a strong build up of electronic “noise” can give your final image a fuzzy or pixelated look which should be avoided. For best results keep the ISO at mid range to keep noise to a minimum and use a slower/longer shutter speed to take collect as much light as possible.
Manual (M)
By rotating the dial and selecting each of the above settings you can get to grips with these three most importance concepts of photography. Get used to adjusting the shutter speed, aperture size, and ISO, until they feel natural to you. Finally it will all come together when you select manual mode. My camera never leaves manual, it’s the bedrock upon which the art of creative photography is born. You can access all your camera’s functions from this single setting. With enough practice you should be able to adjust the shutter speed, et cetera, swiftly and with profiency as the situation demands.
Focus
Sometimes the only difference between a poor image and a stunning capture is focus. A sharp focus will make or break any image and as such it cannot be taught. Focusing a camera in the dark is an art form born from repetition and experience. The only way to master this delicate subject is to get to know your camera. Bridge cameras can be particularly difficult to focus so hours of practice during daylight are essential for nocturnal photography. Since stars are located at infinity you need to be using manual focus unless you have an infinity setting. On a bridge camera focusing is achieved via the “+” and “-” buttons on the rear of the body, or via a manual focus ring around the barrel of your zoom lens. Sometimes after your manual movement of the focus ring there might be a delay before the digital signal makes the change you made. This can be very frustrating so take your time and make small movements until your stars are pinpoints of light. I recommend using the camera’s large LCD screen rather than the electronic viewfinder (EVF) which often are of very poor quality.
In the middle of the night many of your subjects may not be visible on your LCD screen so you will need to focus on a brighter object first before taking an exposure of your target. Bright planets such as Venus and Jupiter are perfect for this including the bright stars Vega and Arcturus if they are at a reasonable altitude. If you cannot see any of these then focus on a distant light source on the horizon such a streetlight which will get you close enough. Using this as a reference you can make small adjustments by previewing the image on the LCD screen until you achieve pin sharp stars. A good tip is to focus the camera at infinity during daylight, or evening twilight, then mark that position with a line over the lens barrel and focus ring using tipex or a permanent marker. Later, under the cover of darkness, you can quickly re-align this position using the light from your mobile phone to save time.
Putting It All Together
You are now armed with the basic ingredients needed to take stunning wide field astronomical images. The theory is simple. Your camera is mounted on a tripod, the aperture is wide open with a long shutter speed, and your ISO is set at 400 or higher. Using the camera’s self timer you then take an exposure. If the night is dark and clear then you will have just taken a very nice image of the stars, perhaps even showing the soft glow of the Milky Way. Glowing with enthusiasm you end up spending the next few nights imaging everything you see until you come to the conclusion that your images are not that good. Some are too bright, others too dark, and even the Moon looks blurred when you experimented with your zoom lens. This is because there are no text book settings which will provide you with the secret recipe for imaging all the various phenomena in the night sky.
Depending on your target, the time of night, Moonlight, or the movement of the object itself, you will find that a specific collection of settings are needed at a particular time on a given night to get the best result. For example: An exposure of 30 seconds would record all the stars of Orion, however if this famous constellation is rising or setting in bright twilight a faster shutter speed and/or lower ISO number will be needed. A conjunction between the crescent Moon and planets will also require that delicate balance between sensitivity and movement of the Moon itself due to the Earth’s rotation. Sometimes you will want to deliberately show motion by selecting a slow shutter to capture the sweeping dance of an aurora. What if there’s a bright Moon in the sky? You may get an overexposed image, so closing down the aperture will darken the image sufficiently to allow you to maintain that shutter speed. You can even use this to make a more creative image by capturing foreground movement such as car trails. Why not try noctilucent clouds against twilight? Here a short exposure (i.e. between 5 and 10 seconds) with low to moderate ISO setting (i.e. between 100 and 400) and an open aperture (i.e. lowest “f” number) will get a result. This is the art of “bracketing” your exposures, bracketing simply means taking several images using different settings until you find that sweet spot. This is the advantage of digital photography.
Conclusion
If you put to practice all of the above techniques then you should have developed a good understanding of photography and perhaps have even taken a few very good images which you have showed off to your friends and family. But don’t stop there. With time you will be able to look at the sky and instantly know what settings you will need to use based on your experience. Now it’s time to take it to the next level, forget about the rule books and make night sky photography an extension of your own personality. Be creative, be different, seek the unusual, and compose your images with the confidence that your images will stand out from the rest. Do you want to be an exceptional photographer? Seeking advice on the matter I once asked an experienced photographer friend of mine this same question, he said,''make sure to use the three P's''. I said to him that I’m certain my camera doesn’t have that setting, to which he replied''practice, practice, practice!'' * This was written for a US magazine.
Martin McKenna