ORIGINAL: OzyDave
That really is a neat photo. I don't know how you got a shallow depth of field but still got motion blur on the prop. Do you know the exposure and shutter speed used? I love how the photo tells a story.
First, I have to agree with you...I love photos that tell a story. That one's got just enough "arm" in it to suggest activity, but not so much 'person" to take away from the motor...and the blur/smoke are JUST right to tell us the motor is purring along. Really a nifty shot.
As for the shallow DoF w/ blur, consider this:
if that engine's idling, it's probably turning what...1000-1200 RPM? Let's call it 1200 for nice easy math. So, 20 rev every second (1200/60), or 1/20th rps. Looks like we got about 10 degrees of prop arc there, so 1/36th of a rev. 1/720th of a second as an estimate. Closest standard shutter speed to that is 800.
With a 1/800th shutter speed, an f 2.8 is not unusual on a cloudy day, especially with a low ISO, which that appears to be due to the lack of grain. It would also give us a pretty shallow DoF...so...I'm gonna guess:
f 2.8, 1/800th of a second, iso 200.