Sunday, August 29, 2010

Chasing The Stars: A Night Photography Tutorial I

Part I – Introduction & Tools

Crowning JewelI believe that night photography is one of the best ways to learn about photography. There are many reasons for this. One of the most important is that it forces you to learn the mathematical relationships between exposure variables (shutter speed, aperture, and ISO). These relationships are become ingrained in your mind and are eventually transferred to other types of photography. Knowing how to manipulate these variables to create the perfect exposure for a situation is one of the keys to photography. Night photography also requires that you know how to operate your camera in the dark. You should be able to change modes, shutter speed, aperture, ISO, focus mode, etc. all by touch. Finally, since night photography with digital techniques is still in its relative infancy, it is still very exciting to see your results. You will rarely find people with the same images which encourages you to take more!

In this three part series I will cover some of the basic concepts and techniques of night photography. This will include everything from gathering the necessary tools for a shoot, to taking images at night, to post-processing the images. I will also discuss some frequently asked questions such as:
  • When do I use a single exposure versus stacked exposures?
  • How do I find the right exposure?
  • How do I create the circular star effect?

The question I receive most often is, "How do you decide when to use a single long exposure and when to use stacked long exposures?" First we need to know what the differences are. A single long exposure is exactly what it sounds like, just a standard exposure with a shutter speed measured in minutes (or hours). Whereas a stacked image is one where many long exposures (say, 30 seconds - 10 minutes each) are stacked together with software to create a single image. These two methods can give you very different results and both have associated pros and cons.

Single Exposures
Mukilteo MagicSingle long exposures have been the standard in night photography since the days of film. It simply requires a shutter (cable) release and some patience.

Advantages over stacked exposures:
  • You can get a properly exposed image with very little ambient light without using a high ISO value
  • Great for cloud motion images
  • Takes up little space on a memory card
  • Fast post-processing
  • Will overexpose quickly with too much ambient light (e.g. cities, full moon, dusk/dawn, etc.)
  • More long exposure noise to be subtracted from image (can severely detract from image for shutter speeds greater than 2 hours)
  • Total time for exposure is two times the shutter speed with long exposure noise reduction on (a must for shutter speeds over 30 seconds)
  • Eats battery life. You risk losing the image if the battery dies in the middle of processing

Stacked Exposures
Lone GiantStacked exposures are relatively new with the advent of digital photography. They require special software to stack several exposures together to create a composite image.

Advantages over single exposures:
  • Great for startrails when there is moderate to bright ambient light (e.g. cites, full moon, dusk/dawn, etc.)
  • No long exposure noise reduction is necessary
  • You can use a higher ISO value since ISO noise and long exposure noise will be averaged out in the resulting image
  • Easier on battery life. You can just shoot until the battery dies or until you're out of memory
  • Typically doesn't handle clouds well
  • Takes up a lot of memory card space
  • Takes much longer and is more work during post-processing since the images must be stacked (computers with a lot of memory are very helpful here)
  • Really only useful for startrails

This tutorial is written for dSLR users, but almost all cameras have the capacity to take night photographs in one form or another. Here we will discuss certain tools that will make life much easier.

Most dSLR's will work for night photography. Newer cameras though, generally have better noise properties and built-in noise reduction than older ones. It is important that you know how to access and change the settings in your camera by touch or memory. These settings include: shooting mode, shutter speed, aperture, ISO, and long exposure noise reduction. Furthermore, you should also learn where the cable (shutter) release port is and how to plug this in by feel (not a trivial matter on some cameras).

Choosing a lens for shooting night images is really a personal choice dependent on the composition you want. I generally like shooting wide angle (12mm - 24mm on a full frame camera) images to get more sky. You should know how to switch your lens from auto focus to manual focus and how to turn image stabilization on and off. Finally, since the goal of many night images it to capture what little light is available, having a wide maximum aperture (f/4 or wider) is very helpful as it reduces the need to use a higher ISO.

Other Gear
Other necessary pieces gear for night photography include:
  • Sturdy tripod
  • Cable (shutter) release (with timer, interval, delay settings if possible)
  • Battery grip
  • Extra (fully charged) batteries
  • Calculator (if you don't like doing math in your head)
  • Warm clothes (it gets cold at night)
  • Headlamp/flashlight
I use a timer release since it allows me to program the delay, number of shots, interval between shots, and any shutter speed I want. Without a timer you are forced to use either the longest built-in shutter speed (usually 30 seconds) or time the exposures manually (which means you have to babysit the camera).

There are a lot of software choices out there for processing digital images. The basic necessities include a RAW converter such as Adobe Camera RAW (ACR) and image editing software such as Adobe Photoshop (PS). Additionally, several vendors sell plug-ins for these programs which can enhance your editing capabilities. I really like Nik Software's Viveza 2 (global and selective editing) and Dfine 2.0 (noise reduction).

In order to stack images some special software is required. If you already own Adobe Photoshop there is action that you can download (here) that will allow you to simple stack all the images in a folder. Otherwise, if you are a Windows user there is the Startrails program which can be used. I have never found another option for Mac users.

Finally, there are hundreds of other small tools out there to enhance your photographic experience, including applications for your smartphones. I've written an Android application that allows you to calculate equivalent exposures, which as we will see in Part II, is an essential part of finding the proper night exposure. To check it out search for "Exposure Calculator" (by RAWapps) in the Android Market.

Coming up next in Part II - Trip Planning & The Night
Trip Planning - What, Where, When, & How Long?
Composition - Polaris, Stars, & Foreground
Test Shots - Default Settings (custom settings)
ISO & Aperture Considerations
The Shot - What to do?


Mike said...

Great tutorial! I can't wait to see the next one to see the rest of the process! thanks!

Anonymous said...

It's really a good tutorial! I've waited for two months for the 2nd issue! I really want to know how you determine the exposure for each photo in the stacked ones.

Reid said...

Thanks, I apologize for the delay. I've been going through job interviews and and now getting ready to move to Wyoming. Unfortunately, my photography time has been greatly reduced until we're settled. :-)

Robert Jacko said...

Thank you for sharing the information and I agree with this as capturing a photograph during day time is very easy for all but, the most hardest part of capturing photos is during night but, this can be resolved by controlling the camera shutter speed, exposure, lens etc.

There are number of classes who are providing the service of digital photography lessons for day and night and while surfing on internet, I came across a site named as My Photo Sharing Secrets who is providing the service of digital photography for beginners.