How can I make iPhone long-exposure light trails look thinner?
Asked 10/29/2018
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2 answers
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I’m shooting car light trails with an iPhone 8 Plus on a tripod using a camera app that lets me control shutter speed and ISO. I can get the long-exposure effect, but the trails look wider and more blurred than the thin single red or white lines I often see in other photos.
Since I can’t control aperture on the phone, is this mainly caused by too much light or overexposure? Would lowering ISO help make the trails appear thinner, and if so, should I compensate by increasing shutter time to keep the rest of the scene bright enough?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
7y ago
2 Answers
1
Your hunch is probably on the right track. Assuming that the thickness of the light trails is due to overexposure of the moving light sources, then reducing the ISO will reduce the apparent intensity of the light trails.
Note that, depending on the light sources creating the trails, the actual size might not decrease much. Headlights and tail lights on vehicles are not point sources of light, so they won't actually produce smaller light trails if you reduce the ISO. However, because their brightness would be reduced, the trails will certainly "feel" smaller.
Note also that if you decrease ISO, the brightness of the entire scene will be reduced, so if you want to keep the background the same brightness, you'll have to increase the exposure time accordingly. E.g.: if you halve the ISO, you should double the exposure time.
Originally by user11924. Source · Licensed CC BY-SA 4.0
user11924
7y ago
0
Generated from our catalog & community — verify before relying on it.
Yes—if the trails look too thick because the lights are overexposed, lowering ISO can help reduce their apparent width and intensity.
A few things to keep in mind:
- Lower ISO makes the whole image darker, not just the trails.
- To keep the background exposure similar, you’d usually lengthen the shutter time to compensate.
- Vehicle headlights and tail lights are not true point light sources, so they won’t become razor-thin lines just by changing ISO. Lower exposure mainly makes them feel smaller and less bloomed.
So the practical approach is:
- Lower the ISO as much as your app allows.
- Adjust shutter time to keep the overall scene bright enough.
- Expect some limit from the actual size/brightness of the car lights and the phone camera optics/sensor.
In short: thinner-looking trails are mostly about reducing overexposure, but the physical size of the light source also matters.
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