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I'm trying to do long exposure photos with car headlight trails and am finding the results a little disappointing due to the low 'impact' of the light trails. I believe there are a few things affecting this, namely

  1. length of exposure (currently limited to about 90s at min ISO and aperture)
  2. the amount of traffic
  3. the level of light given off by street lamps

I believe 1 & 2 can be fixed by the addition of an ND filter and choosing a busier time to take the pictures, but am not sure how I can address 3. Is there some sort of filter I can use which will minimise the effect of the street lamps without cutting out too much of the light from car headlamps/tail lamps?

Here's an example of what I've done so far:enter image description here

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The solution to #3 is to find a location without those horrid Sodium Vapor Lamps, preferably one with no street lights at all. Then you can take much longer exposures and you don't need to worry about # 1 and #2. And you will have light at wavelengths other than a narrow band around 2700°K. On a night with a moon in its second quarter (which means it is already in the sky just after sunset when the most vehicular traffic at night is usually seen) you'd be surprised how much can be illuminated with the moonlight during long exposures.

This was a proof of concept shot I did a while back. Although there are no light trails in this one, the shadow of the parked car is thrown by a nearly full moon. The barely visible secondary shadow of me and my tripod (in addition to the darker one thrown by the moon) at the left edge is thrown by a bright street light about 1000'/300m away. At the time the trees near the water were dark silhouettes to my naked eyes. ISO 2500 for 30 seconds at f/2.8. Exposure reduced two stops in post.

Dropping the ISO to 100 and narrowing the aperture to f/11 would allow exposing for 1/2 hour at the same exposure! But that would make any short duration light trails pretty much invisible. So try using a wider aperture such as f/5.6 and you could expose for 7-8 minutes. If the light trails still aren't bright enough, raise the ISO a little and shorten the shutter speed by the same amount. The ambient light will be at the same exposure level, but the headlights and taillights will get brighter relative to the ambient. If the light trails are too bright then stop down a little and increase the shutter time by the same amount.

Moonlit parking lot

  • "But that would make any short duration light trails pretty much invisible. So try using a wider aperture such as f/5.6 and you could expose for 7-8 minutes." Wouldn't that also increase the light given off by the street lights? – BBking Aug 21 '14 at 1:07
  • Not if you are following the first suggestion in the answer and shooting where there are no street lights. – Michael C Aug 21 '14 at 1:36
  • Using shorter exposure/wider aperture instead of longer exposure/narrower aperture would not increase the brightness of the constant light sources (such as street lights) but only the brightness of the intermittent ones (such as passing cars that are not in the frame for the entire exposure). – Michael C Aug 21 '14 at 1:45
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The brightness of trails is controlled by the flux of light hitting the sensor and its sensitivity. So, you can either increase ISO or open up the aperture or both. In any case, remember that each one has another impact: Opening your aperture decreased depth-of-field; increasing ISO adds noise. When you use an ND filter you are reducing the imprint of light trails because much less light is reaching the sensor.

The total trails in the image is controlled by traffic. More traffic will super-impose lots of trails which will add to the image. It may also break the flow, particularly in places where traffic does not move uniformly. The best is a busy highway segment. This is when ND filters are most useful.

Your position is highly dependent on how you want to frame the shot. When you are closer, trails will appear larger but tend to look less smooth because of different headlight positions. For this photograph from Chiclayo (Peru) I tried about a dozen times until several cards make full circles.

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I'm not quite sure what you want to do with the street lights but number 2 is your best bet if you want the impact of the car's head lights to be better.

The below image was only a 20 second exposure:

Gold Coast, Queensland

Below image is with 30 seconds: Few cars

Notice how there isn't much light from the headlights? This is because I only got about 2 or 3 cars in the image.

Again, 30 seconds exposure but with more traffic: Camera facing oncoming traffic Camera facing leaving traffic

Above, the camera was facing oncoming traffic while the one below, the camera was facing leaving traffic, hence the more white light above and more red light below.

Before I go further, is this what you mean? Because I'm not sure if you want the street lights to have a lower impact while trying to have the car's headlights have a higher impact.

EDIT: It looks like in your image, there were only about 3-4 cars in it. My last two had about 20 cars in the shot. Heavy, bumper-to-bumper traffic, which increases the impact of the headlights.

  • "Because I'm not sure if you want the street lights to have a lower impact while trying to have the car's headlights have a higher impact" yes this is what I'm after. – Matthew Dresser Aug 20 '14 at 13:01
  • Well, I'm sorry. The only way I can think of is reducing the shutter speed and increasing the amount of cars. Just a side question, are the street lights in my images not what you are after? – BBking Aug 21 '14 at 1:10
  • My focus was more on how to minimise the effect of light from street lights in relation to the car lights, rather than any interest of how the street lights look themselves. – Matthew Dresser Aug 21 '14 at 11:29
  • I didn't mean how they look... To put it simply, do the street lights in my images have too much or too little impact to what you are trying to achieve? The only way to reduce the impact of the street lights is to reduce exposure and increase the light (of which you want more impact). That is to say, reduce exposure and increase traffic flow. – BBking Aug 21 '14 at 23:47
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You could try to deal with the street lamp lights in post processing. The lamps don't move and radiate at constant intensity, so the information contained in the picture due to the street lamps is not so difficult to extract. You can take a picture with a short exposure time when there are no cars to get the pure street lamp contribution. If you then do a long exposure you can subtract from that the short exposure picture to get to a hypothetical picture that you could have taken if there had been no street lamps. But to get this right you need to apply some transforms on the brightness of both pictures, so you do have to experiment a bit with this.

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