Taking a digital picture of a spinning fan...

If I were to use a typical consumer digital camera to take a photo of a fan that was running at 2500-5000 RPM, would the fan appear to be “still”? IE, given the CCD speed in a consumer model camera, would a photo of the blades of a running CPU fan look blurred or sharp?

Yes, this about a possible Ebay ripoff. Unfortunately, I don’t have a camera handy, otherwise I’d experiment for myself. I’ve also got no idea how to do the math to figure out shutter speed vs. rpm, because I’m a big dummy.


Yes and no. It will depend entirely on the ISO, Shutter speed, Aprature and possibly most important, if a flash was used.
Yes, you can stop the action of fan (I did it just a few days ago with a cheapo camera) and you can leave the motion in.

BTW what is the ebay issue?

If a Canon PowerShot S70 counts as “typical consumer”, you bet your ass you can get pix in which the blades appear totally still. And well-focused enough you can see the dust bunnies sticking to the frozen-in-motion blades.


You can also (using different settings, natch) get an artistic blur, not only from spinning fans but things moving a whole lot slower.

A fan running at 500 rpm travels 4.3 degrees per millisecond.

Hmmm. Oh well. There goes one argument in our favor.

The boss bought a mobo/CPU combo off of Ebay, and it was DOA. The seller sent us a pic of the board sitting in front of a monitor, hooked up to a PSU, and (supposedly) POSTing. Noting that the CPU fan didn’t appear to be spinning, he asked me to dig in to it.

I’ve got to admit that he’s being a little tenacious over 40 bucks - and it’s his fault for buying production components off of Ebay - but still.

Thanks folks.

Yes, it is possible, especially if the picture is flashed, as flash durations generally range from 1/1000 - 1/20,000 of a second, depending on the power of the unit and the power outputted.

If it’s an indoor photo, and there is no evidence of flash, then I would assume the fan is most likely not running.

If you have a copy of the picture, it’s possible that the EXIF information is still intact, and that would tell you all the settings of the camera used. I wouldn’t bet on the information being there, but it’s a distinct possibility.

You seem to have messed up something in there; the correct figure is about 3 degrees per ms. I also double-checked here.

Yup. I probably had the calculator set for metric radians or something.