"Low-Light Action," 31 January - 13 February 2011

[keithsnell]

One of the situations that tests our abilities as photographers (and pushes the limits of our camera's technical capabilities) is low-light action photography.  Unlike more static subjects where we can simply opt for a longer shutter speed to get the appropriate exposure, low-light action photography will require us to pay strict attention to keeping our shutter speed high enough to prevent motion blur (unless that motion blur is intended for artistic purposes).

Doing well at low-light action photography requires us to know our cameras capabilities well enough that we can chose an acceptable compromise between shutter speed, aperture and ISO.  The cameras I use vary greatly with respect to the amount of signal amplification (bumping up the ISO) that can be applied before the digital noise in the image becomes objectionable.  By paying close attention to the results I achieve, I know exactly what quality of image (signal to noise ratio, color characteristics, etc.) I can expect from an image shot at ISO 800, 1600, 2000, 2500, 3200 and 6400 on my D3 (and on all my other cameras).  In a way, ISO becomes my "quality indicator" and I will use my ISO setting to balance my desired shutter speed and aperture with my desired image quality/noise.  If my output is for the web, or for a 4x6 print, I know that moderate amounts of noise will become invisible when I reduce the image size for output.  With those types of output I feel comfortable pushing my ISOs up to 3200 (and sometimes ISO 6400 in a pinch) in order to get a faster shutter speed.  If instead, my final output will be a large print, then I might not feel comfortable shooting above ISO 1600.

But of course everything is a compromise.  If shooting at ISO 1600 will result in a shutter speed that is too slow to eliminate motion blur from the subject movement, then I will usually make the decision to use a higher ISO and accept a bit more noise in the image.  Typically a little "grain" from the digital noise in the image is less objectionable than a blurred image.  (And noise reduction software can sometimes rescue an image that is too noisy, but it is hard to recover an image that is blurred due to motion.)  

And aperture is almost always sacrificed for more shutter speed in low-light action photography.  While most lenses perform a little better when stopped down from wide open, and it is nice to have more depth of field on the scene, it is often possible to adjust our composition and accept a slightly soft background for the sake of gaining a little more shutter speed.  Again, the very slight loss in clarity from  shooting a lens wide open is often easier to correct with a bit more sharpening in post-processing, while the uneven blur from subject movement is more difficult to compensate for.

There are other techniques that I can use as well to try to avoid motion blur in the image.  There will almost always be a lull (or significant slowdown) at some point in the action.  By timing my shots so that I capture these momentary pauses, I can reduce the blur caused by a moving subject.

It's also important to understand the limitations of your camera's autofocus system and know what autofocus settings and techniques might help you acquire focus more consistently when the camera is struggling in low light.  Canon's excellent white papers provide a bit more detail on how their cameras work "underneath the covers," and are worth reading in order to better understand and utilize the capabilities of the system.  The Canon white paper for the 1D III gives technical background on the autofocus system that can help us adjust our settings and technique to optimize focusing in low light.  According to the white paper:  

"The center AF point is a cross-type sensor. It is vertical-line sensitive with maximum apertures as small as f/4, and horizontal-line sensitive with maximum apertures as small as f/8. If the maximum aperture of the attached lens or lens/extender combination is f/4 or faster, high-precision, cross-type focusing is possible. If the maximum aperture of the attached lens or lens/extender combination is f/8 or faster, horizontal-line sensitive AF is possible. Compared with the other 18 cross-type AF points, the center AF point's focusing line width is larger while the fill factor for each pixel is larger (f/2.8 field of view). Also, the number of focusing lines increases along with the brightness (f/5.6 field of view) to attain higher precision. Gross defocus is also detected."  

"The 18 cross-type AF points other than the center AF point detect vertical lines at f/2.8 and horizontal lines at f/5.6. If the maximum aperture of the lens or lens/extender combination in use is f/2.8 or larger, high-precision, cross-type focusing is possible.  Also, if the maximum aperture of the lens or lens/extender combination in use is f/5.6 or larger, horizontal-line sensitive AF is possible."

Translation?  In extremely low light Canon's AF system will acquire and hold more accurate focus using the center autofocus point than with the other surrounding AF points.  In addition, the system is more sensitive to horizontal lines, so you can "help" the system by ensuring the AF point is placed over a high-contrast horizontal line during initial AF acquisition, then shift your composition as required.

Nikon has similar (although not quite as detailed) "pro guides" that provide recommendations for optimizing AF settings in challenging situations.  

I'll add more to this post in the next couple of days, but wanted to give folks a "heads up" on the upcoming assignment.

Improving our low-light action photography requires that we take the time to experiment and critically examine our results (and practice, practice, practice), so I think we would benefit from making this a two week assignment.

[Michele]

Hmmmm...  I wonder where this idea came from for the assignment?    I know for a fact that I will be working hard on this assignment.  Thank you, Keith. You're a star!

[Michele]

Just wanted to delete this.

[keithsnell]

Well Michele had a good point in her post that she deleted.  She suggested the use of panning as an option for low light action. That is a very good suggestion.  As Michele mentioned, it's tough to get right, and takes a lot of practice.  As she said in her post, the key is trying to keep a smooth even motion that matches the speed of your subject across the scene.  Some image stabilized lenses have an "action" setting that is appropriate for use with panning.  One advantage of this technique that Michele mentioned was that you can convey motion based on the "motion blur" of the background movement behind your subject.

Very good suggestions Michele.

Keith

[Michele]

I deleted the post because I figured that's an "extra" that wasn't what you wanted to emphasize in this assignment.   Why should I complicate it more?  I would love to try that in another assignment one day though.  Panning to catch an action, that is.

How do you delete a post anyways?  

P.S.  I love my new avatar, thank you Keith.

[keithsnell]

I deleted the post because I figured that's an "extra" that wasn't what you wanted to emphasize in this assignment.   Why should I complicate it more?  I would love to try that in another assignment one day though.  Panning to catch an action, that is.

How do you delete a post anyways?  

Yes, panning would be fun to try in a future assignment, since it really is a specialized technique.

Hmmm, seems I have the option to delete posts only turned on for moderators.  I'll have to see if there is a way that I can set the options so that people can delete their own posts.

Keith