Tag Archives: Stars

Back in August 2013, the Mile High Wildlife Photography Club (MHWPC) hosted acclaimed photographer and planetary scientist Dr. Roger Clark.  With his presentation on astrophotography tips and the annual Perseid meteor shower taking place on August 10-13, I was really inspired to take night photography more seriously and really see what I can do with my current equipment.  Unfortunately Dr. Clark’s MHWPC meeting was moved a week and I was unable to attend his lecture.  I did have several exchanges with him afterwards, however, and his insight was vital in improving my understanding and learning of nighttime photography.  As a result, it is the intent of this article to share my lessons learned, tips and other less common useful information to assist other photographers with their night photography.  Successful night photography, like most photography, is comprised of preparation, execution and post-processing.

I’ve found myself on many occasions outside at night witnessing a wonderful night sky, wishing I had a camera or alternatively sitting there with my camera and wishing I had a clear sky.  Although you can’t always predict Mother Nature, good preparation can increase your chances that she’ll help you get that perfect shot.  So, here are some useful links to assist you with your pre-night shoot preparation.

• The Photographer’s Ephemeris (TPE) to determine the Moon rise / set times and relative location in the sky.
• ClearDarkSky is a really useful website for predicting the cloud cover, transparency, seeing and darkness.
• Stellarium is a planetarium desktop software, which is great for searching the night sky, seeing where the Milky Way will be, planets, constellations, nebulae, etc.
• US Navel Observatory provides a searchable moon and sun database, which is handy for researching the moon phase and set to obtain the darkest night possible
• NOAA Predicted Geomagnetic Index is useful to check on the probability of seeing an aurora.  If the Kp turns up above 5, then there’s a good chance you may see an aurora. (Thanks Dr. Clark for this site)
• POES Aurora Satellite Image is useful to check on the position of current aurora oval.  (Thanks Dr. Clark for this site)

Taking wonderful night images comes down to the same photography basics as any photograph; aperture, ISO, exposure and focus.  It’s the trade off of these that the photographer is faced with in order to capture their desired image.

Not surprisingly, a fast lens (F2.8 or less) is ideal for enabling the photographer more flexibility in trading off ISO and/or exposure to capture their desired image.  A fast lens is especially required to effectively capture meteors, where you only have a fraction of a second worth of light available for the exposure.

Full frame DSLRs are inherently better at minimizing the noise at high ISO’s when compared to cropped DSLRs because of their large pixel and sensor sizes, however. all exhibit an amazing ability at capturing images with high ISO’s.  Regardless of the DSLR used though, they should be capable of taking good photos at ISO 3200, 6400 or even higher.  With the advances of noise reduction software, such as Lightroom, Topaz DeNoise or Nik Dfine, photographers can really push their ISO settings and still produce really high quality results.  In addition, the built in camera long exposure compensation can be useful for reducing noise.  Using this feature typically doubles the processing time, but can greatly reduce the noise in the recorded image.

I have found that the exposure trade-off is the most important one, with many misconceptions on it.  Too short of exposure, then you aren’t able to acquire enough light to effectively capture all of the stars, stellar dust, airglow, etc.  Too long of an exposure, then your image will have star trails.  This is obviously sometimes a desired effect, but if you are trying to photograph the Milky Way for example, then this may not be desired.  Short star trails just make the stars look blurry since the stars appear larger than they should be.  An example of this is shown below in the following figures.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

So, how long can you expose your image before star trails are visible?  You may have read about recommendations of 30 seconds or the 600x rule, which states that for a full frame camera if you multiple the focal length used times the exposure and the resultant value is less than or equal to 600, then the stars should appear without trails.  This ‘rule’ is misleading however, which after discussing it with Dr. Clark, he clarified that the real limiting factors are the focal length, exposure and camera sensor pixel size, also known as the pixel pitch.  During long exposures, the light received on the sensor from a star will transition from one pixel to the next as Earth rotates relative to the stars.  With a recommended maximum pixel drift of 2-3 pixels, the sensor pixel pitch has a direct impact on the useful exposure duration for images without star trails.  Dr. Clark has a great overview of the impact of pixel sizes on his website.  Astropix has a detailed table of the pixel pitches, sensor sizes, etc. for numerous Canon and Nikon cameras which is available here.  The following table captures the estimated exposure times with respect to sensor pixel pitch and focal lengths for a few common Canon and Nikon cameras.

Additionally, unless intended, what good is an out of focus photograph?  Using mirror lock-up, a remote shutter release and a sturdy tripod are essential tools to help mitigate against camera movement impacting the recorded image.  However, focusing on the stars at night can be a bit tricky as well given the limited light available.  Because of the reduced light available; auto-focus really doesn’t work very well.  As a result, using manual focus is recommended.  Switch off auto-focus on the lens and then use live-view to manually focus on a bright object in the distance, such as a star, planet, the Moon, a street lamp or city.  Every lens is a bit different, but generally starting your lens depth of field just outside of infinity is a good place to start.  It’s a good practice to make note of the resultant depth of field setting to quickly focus in the future with that particular lens as well.

If longer exposures are desired, but star trails are not, then additional equipment such as the AstroTrac or another astrophotography stabilization tripod mount may be used for accurate exposures of 5-minutes or more.  Alternatively, star trails can be a very creative lighting technique making for wonderful photos.  Instead of very long exposures of several hours, these long star trail photographs are usually stitched together using 100’s of 30-second exposures with software like Adobe Photoshop, Startrails.exe or Image Stacker.

Finally, post-processing.  This is very subjective, but if you want to keep the photograph white balance accurate then know that the sky is really ‘warm’ because of all of our dust in the atmosphere and that the green air glow really should be there.  If you shoot RAW, then it’s easy to change this after importing your photographs.  If shooting JPEG, then it’s worth spending sometime in the field adjusting the white balance.  Some great examples can be found on Dr. Clark’s website.

Regardless of the photography equipment you have, you can still take exciting nighttime photos.  So go out there, try to capture the night and have fun with it!

Useful Links:

1)  dpBestFlow detailed information on sensors.  Provides a good overview of terms and information relating to sensors.

2)  I encourage the reader to visit Dr. Clark’s website Clarkvision, which is full of detailed photography tips, information and of course his wonderful images.

3)  A couple informative links for How To Photograph Star Trails and from Petapixel, How to Create Star Trails from Start to Finish

4)  A very thorough guide for Astrophotography from Astropix.com