Adapt to the Dimness
Hard truth: The tall, narrow walls that make a slot a slot also make it pretty dark. Your eyes adjust, but a camera will struggle to gather enough light. Best option: Keep your aperture small (so the full canyon stays in focus) and your ISO speed low (to avoid graininess; see below), and use a tripod so you can slow your shutter speed as much as needed (usually to between 1/60 and 10 seconds).
Shoot Into the Light
Viewers’ eyes are attracted to bright areas, so compose with the brightest walls farthest away to draw their gaze deep into the scene. Dark walls in the foreground can frame and highlight beautiful patterns.
Manage Bright Spots
To avoid a big, distracting blown-out zone, look for areas lit by reflected rather than direct sunlight. Avoid including the sky for the same reason. If you must include direct light, several smaller bright areas are preferable to one large spot (because their narrower shapes tend to complement the scene’s existing lines).
Put the Dust to Work
Slot canyons are often dusty, so don’t plan on switching lenses (bring a zoom). Upside: Dust particles can create visible beams of light, which add wonder and energy to your image. Hide or crop out the beams’ endpoints to avoid direct sunlight splotches (as above). If there isn’t enough dust to see the beams, try tossing a handful of sand.
Key Skill: Master ISO
How sensitive is your camera to light? Depends on its ISO setting. The higher the ISO, the less light you need to capture an image. But at higher ISOs (especially 800 and above), distracting dots (noise) start to show up in your photos. So, as a general rule, use an ISO below 500. Pro tip: To speed your process, boost your ISO high for quick, short-shutter-speed test shots as you lock in your framing, then lower ISO and lengthen exposure time to capture your best shot in higher quality. That way, you won’t have to take 30 shots at five seconds each to score your perfect image.