The brightest light source in this room was the "EXIT" sign above the back door. Other light sources include small CFL bulbs under black lampshades and cool white tube lights in an adjoining room. Yuck. 70mm 1/160sec F/2.8 6400 ISO/ASA

I do a lot of my personal shooting in miserable lighting conditions. I’m talking about tango “clubs” that are cobbled together in an old warehouse, dive bar, dance studio, or repurposed factory with high ceilings (black, of course) with Christmas lights and CFL bulbs bounced off exposed brick and dance mirrors providing the light. It’s a challenge. I think there’s a team of people somewhere brainstorming ways to make the light for tango events really crappy. Regardless, I love to shoot tango events. It’s usually my friends out there dancing and I love to get good photos of them doing what they love. It’s also good practice. Working right at the edge of what my equipment can handle is good.

Here are a few things that I’ve learned about working with fast lenses in bad light.

1. Most cameras are calibrated and optimized to accurately focus with lenses having a maximum aperture of f/2.8.

2. If your lens has a larger maximum aperture than 2.8 you are going outside of the comport zone of your camera’s autofocus system.

3. Stopping down a f/1.4 lens to f/2.8 doesn’t help because autofocus is performed with the lens wide open. It may help improve image sharpness and focus simply because you’ll have more depth of field at f/2.8 than at f/1.4, but it does not improve autofocus performance. In fact, I think it hurts autofocus performance substantially to work with a lens faster than f/2.8. If you have enough light to work at F2.8, use a lens with f/2.8 maximum aperture. Even moving from a lens with f/1.4 to f/1.8 will improve your autofocus performance.

The good news is that if you plan to do a lot of autofocusing in the dark it’s better to buy that cheaper 85mm f/1.8 than the much more expensive f/1.4 or f/1.2 version. The bad news is that you won’t have access to that extra 2/3 or full stop of light for freezing motion.

4. Manually focusing in the dark is EXTREMELY difficult, especially when with working with modern full frame cameras that work in light so low your eyes already have trouble focusing. Doing this with moving subjects is nearly impossible. Eyes have apertures as well.

5. Image stabilized lenses (either VR or IS) are fantastic, but they suffer from the major drawback of not keeping the subject from moving. I doubt anyone will ever make a subject stabilizer.

6. You can’t use the AF-assist beam on your strobe in situations where your subject is continuously moving. AF-Assist beams only work in AF-S (single-servo) mode, which does not continuously track subject movement. Believe me, I’ve tried it, a lot and single servo mode just doesn’t work for movement. Way back in my sports photography days we used to pre-focus and shoot when the subject came into that area. Trap focusing, which is a method of using pre-focusing and AF-Single mode with focus priority release to automatically trip the shutter when the subject comes into focus can work, but you’ll never get a decisive moment with that technique. It’s something that photographers use when they need to leave a camera out in the woods to capture images of animals which walk through the focus trap.

7. It helps to set your AF-C (continuous servo) mode to prioritize focus over release. Nikon’s allow you to do this.  I don’t know about Canon. This will slow down your frame rate and can be a bit infuriating when you miss that decisive moment while your lens searches for critical focus, but it will give you an almost infinitely better in-focus to out-of-focus shot ratio.

8. If you are happen to be shooting social dance styles like salsa or argentine tango, it helps to shoot with the music. Learn the timing, count the beats, shoot on the beats. It works better than trying to predict what a leader will do and how a follower will respond. Social dancing is a conversation with rhythm. You never know the words but you can count on the cadence most of the time.

Obligatory Reference Material: http://nikonrumors.com/2011/03/28/auto-focus-accuracy-a-scientific-cross-brand-analysis-guest-post.aspx/