# Hike Mission Peak and Catch Sunset

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on Apr 20, 2011.

6 of 6 pages

• very cool bob! is this with a long exposure?

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• A former member

I think I know where he got the idea (http://blog.starcircleacademy.com/2011/03/driven-to-abstraction/)! I like it Bob! Trivia question: Bob took this shot by moving his camera while the lens was open... why do the lights look "dotted" instead of continuous?

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• A former member

I actually hadn't seen that blog post. It's an excellent explaination of camera movement and focus adjustment during long exposures though. I really need to read the Star Circle Academy blog more often. May - Yes, it was about half a second exposure at f5 and iso 100. One of the tricks is trying to remember that the movement in the image will appear as the opposite of the camera motion. So in this one the camera moved in a U shaped motion. Steven - That is a powerful question.

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• A former member

Flickering lights and short exposure and fast movement? =)

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• A former member

@Alex - close. Why were all the lights apparently flickering at the same time and rate?

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• A former member

i don't know =) was making a semi-educated guess.

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• A former member

Here is the answer: Nearly every light source in this photo is fed by 60 hz AC current. Our eyes don't notice it, but all those lights are flickering at a rate of 60 cycles per second. The movement of the camera in this case reveals the 60 hz cycle and shows each of the lights as dashed lines. All the lines are similarly dashed because they are all fed by 60 hz electricity. If you take a photograph lit by indoor light without a flash at 1/200 of a second you are likely to notice that sometimes your subject is lit, sometimes not - due to the same flickering lights phenomenon. So, give these each a try and see what you get! PS, I *think* it's possible to use the dashes to measure the angular speed of the camera motion AND the length of the exposure. I think it's also possible to determine the relative distances of each of the lights by comparing the lengths of their dashes. Anybody feel enough geek coming on to take a stab at these?

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