Chapter 21 — Quiz
Twenty-six self-check questions on night and long-exposure photography: multiple choice, true/false with justification, short answer, and a few "what's wrong with this shot?" seeing questions. Answer them before checking the key at the bottom. If you miss one, the key points you to the section to review.
Multiple choice
Q1. A long exposure is best defined as any photograph where: - A) the ISO is above 1600 - B) the shutter stays open long enough that motion becomes visible as blur, streak, or smoothing - C) the aperture is wide open - D) it was taken after sunset
Q2. Why is a tripod the single enabling tool of night photography? - A) it makes the camera lighter to carry - B) it improves autofocus accuracy - C) at multi-second shutter speeds any camera movement smears the entire frame, so the camera must be held perfectly still - D) it increases the sensor's sensitivity
Q3. Bulb mode lets you: - A) brighten the LCD for shooting in the dark - B) keep the shutter open for as long as you hold the release down (for exposures past 30 s) - C) automatically reduce noise - D) fire the built-in flash repeatedly
Q4. When the camera is on a tripod, image stabilization should be: - A) on, for extra safety - B) on, but only for exposures under 1 second - C) off, because the system can hunt for motion that isn't there and introduce a wobble - D) it makes no difference
Q5. The 500 rule (500 ÷ focal length) estimates: - A) the maximum ISO before noise becomes unacceptable - B) the longest exposure that keeps stars as points rather than streaks - C) the number of frames needed for a star trail - D) the hyperfocal distance at night
Q6. Using a 25mm (35mm-equivalent) lens, roughly the longest shutter for point stars is: - A) ~5 seconds - B) ~20 seconds - C) ~60 seconds - D) ~2 minutes
Q7. A light trail is recorded because: - A) the camera sensor glows in the dark - B) a moving light source is bright enough to draw a continuous line as it travels across the frame, while the dark object carrying it doesn't register - C) the shutter fires multiple times - D) the lens distorts bright points
Q8. For sharp point stars (not trails), the ideal lens is: - A) a long telephoto at a small aperture - B) a wide lens at a wide aperture (e.g. f/2.8) - C) any lens at f/16 - D) a macro lens
Q9. Long-exposure noise reduction (LENR) works by: - A) lowering the ISO automatically mid-exposure - B) taking a same-length "dark frame" with the shutter closed and subtracting its hot-pixel pattern from your photo - C) blurring the noisy areas - D) stacking several short exposures
Q10. The main cost of switching LENR on for a 3-minute exposure is: - A) the file becomes much larger - B) the camera is then occupied for roughly 6 minutes (it shoots an equal-length dark frame), so you can't shoot in between - C) the colours shift warmer - D) it disables bulb mode
Q11. Blue hour is the night photographer's prime time mainly because: - A) there are fewer people around - B) the deep-blue sky and the just-switched-on artificial lights are roughly equal in brightness, so both hold detail at once - C) the air is clearer after sunset - D) cameras autofocus better in blue light
Q12. Light painting gives you control of a dark scene because: - A) it raises the ambient light evenly - B) during the open shutter you move a handheld light to selectively illuminate parts of the subject, placing every highlight by hand - C) it forces the camera to use a higher ISO - D) it only works with studio strobes
Q13. To smooth a waterfall into a silky veil, you're typically reaching for a shutter of about: - A) 1/500 s - B) 1/60 s - C) ½ s to a few seconds - D) it can't be done
Q14. At night, autofocus usually fails because: - A) the lens is too cold - B) autofocus hunts for contrast, and a dark scene gives it almost nothing to grab onto - C) the battery is too weak - D) the sensor turns off in the dark
True / False — and say why
Q15. A correct night histogram should be spread evenly across the whole graph, just like a daytime scene. True / False — justify.
Q16. You should always set ISO as high as possible at night to gather the most light. True / False — justify.
Q17. For a star trail, the modern approach is one single very long exposure rather than many shorter frames stacked together. True / False — justify.
Q18. A long exposure can keep the still parts of a scene perfectly sharp while the moving parts (water, traffic, stars) blur. True / False — justify.
Q19. During a 30-second light-painting exposure, dwelling the light longer on an area makes that area brighter. True / False — justify.
Q20. Blue hour lasts for several hours after sunset. True / False — justify.
Short answer
Q21. In one sentence each, state what a long exposure does to (a) a moving bright light and (b) a moving textured surface like water.
Q22. Name the three reliable ways to focus in the dark described in the chapter, in order of preference.
Q23. You're photographing traffic at night and your trails keep coming out too short and broken. Give two different changes that would lengthen them.
Q24. Explain in one or two sentences why a wide lens lets you use a longer shutter for point stars than a telephoto does.
What's wrong with this shot? (seeing questions)
Q25. A photographer sets up on a tripod to shoot car-light trails, leaves image stabilization on, fires the 15-second exposure by pressing the shutter button with a finger, and gets a frame where the streetlights and the static building edges look slightly soft and doubled, even though focus was correct. Name the two distinct mistakes and the fix for each.
Q26. A "long exposure of a busy highway" comes back with crisp, sharp asphalt and lane markings but almost no light trails at all — just a few faint dots. The shutter was a correct 20 seconds and the exposure brightness is fine. What went wrong, and what's the fix?
Answer Key
Q1 — B. A long exposure is defined by motion becoming visible (blur/streak/smoothing), not by a specific ISO, aperture, or time of day. (§21.1)
Q2 — C. At multi-second speeds the camera records its own movement as smear across the whole frame, so it must be held perfectly still. (§21.1)
Q3 — B. Bulb mode holds the shutter open as long as you hold the release — the way to shoot past the usual 30-second limit. (§21.1)
Q4 — C. On a tripod the camera isn't moving, so stabilization can hunt and introduce a wobble; turn it off. (§21.1)
Q5 — B. 500 ÷ focal length estimates the longest exposure that keeps stars as points before the Earth's rotation streaks them. (§21.4)
Q6 — B. 500 ÷ 25 ≈ 20 seconds. (§21.4)
Q7 — B. Only the bright moving light registers, drawing a continuous ribbon; the dark object carrying it doesn't. (§21.3)
Q8 — B. A wide, fast lens spreads the sky's motion over fewer pixels (longer allowed shutter) and gathers more light — ideal for point stars. (§21.4)
Q9 — B. LENR shoots an equal-length dark frame and subtracts its hot-pixel pattern. (§21.2)
Q10 — B. The equal-length dark frame doubles the time the camera is occupied (3 min → ~6 min). (§21.2)
Q11 — B. The balance of sky brightness and artificial-light brightness lets both hold detail. (§21.6)
Q12 — B. You place highlights by hand by sweeping a light over the subject during the open shutter. (§21.5)
Q13 — C. Roughly ½ s to a few seconds gives the silky look; longer for a full mist. (§21.3)
Q14 — B. Autofocus needs contrast, which a dark scene barely provides, so it hunts and fails. (§21.2)
Q15 — False. A night scene is genuinely mostly dark, so a correct night histogram is left-heavy; you only worry if the important midtones are crushed to pure black or the bright lights are clipped against the right wall. (§21.2)
Q16 — False. Raise ISO only as a last resort, after shutter and aperture, because ISO adds noise. Keep it as low as the (tripod-enabled, long) shutter allows. (§21.2)
Q17 — False. The modern way is many shorter frames (e.g. dozens of 30 s frames) stacked afterward, which keeps each frame clean and avoids excess sky-glow and heat noise from one giant exposure. (§21.4)
Q18 — True. That separation — sharp stills, blurred motion — is the whole point and requires the camera be locked on a tripod. (§21.1, §21.3)
Q19 — True. More dwell time means more accumulated light on that area, so it records brighter. (§21.5)
Q20 — False. Blue hour is brief — roughly 20–40 minutes after sunset (and before sunrise); it's named "hour" loosely. (§21.6)
Q21. (a) A moving bright light draws a continuous line/ribbon (a trail). (b) A moving textured surface gets averaged across all its positions into a soft, smoothed mist/veil. (§21.3)
Q22. (1) Manual focus on a bright distant light using magnified live view; (2) autofocus on a bright light/edge, then flip the lens to manual so it can't refocus; (3) set the lens to its hyperfocal distance and leave it (for landscapes). (§21.2)
Q23. Any two of: lengthen the shutter (e.g. 10 s → 25 s); wait for denser, continuous traffic so cars move through the frame the whole exposure; (close the aperture / lower ISO to permit a longer shutter without over-exposing). (§21.3)
Q24. A wide lens spreads the sky's apparent motion across fewer pixels, so a star's drift takes longer to become a visible streak — letting you keep the shutter open longer and gather more light before the stars smear. (§21.4)
Q25. Two mistakes: (1) image stabilization left on while on the tripod (it hunts and softens), and (2) firing with a finger on the shutter (the press vibrates the camera during the exposure). Fixes: turn stabilization off on a tripod, and fire with a 2-second timer or a remote release so the camera is untouched at exposure. (§21.1)
Q26. The road was empty (or nearly so) during the exposure — light trails only draw if lights are actually moving through the frame while the shutter is open. The brightness being fine just means the ambient exposure was right; there simply weren't cars. Fix: time the release to when traffic is flowing (anticipate the flow), and/or shoot where traffic is denser and continuous. (§21.3)
Topics to review by question
- The tripod, bulb mode, stabilization, the separation of still/moving: Q1, Q2, Q3, Q4, Q18, Q25 → §21.1
- Metering, histogram, noise, LENR, focusing in the dark: Q9, Q10, Q14, Q15, Q16, Q22, Q25 → §21.2
- Light trails and smoothed water: Q7, Q13, Q21, Q23, Q26 → §21.3
- The 500 rule, point stars vs. star trails, wide fast lenses: Q5, Q6, Q8, Q17, Q24 → §21.4
- Light painting: Q12, Q19 → §21.5
- Blue hour and timing: Q11, Q20 → §21.6