formula for blurry props

[Timothy Aanerud]

Hi,
Does any have a formula for calculating the shutter speed necessary to blur the prop when photographing a turning propeller?

If you use a high shutter speed when taking a picture of an prop aircraft in flight it will stop the prop. So, I'm assuming a slower shutter speed should help "blur" the prop.

Some where I read that:
1/125 works well for 2 bladed propellers, and
1/180 works well for 3 bladed props.

But prop rpm must somehow figure into this too. So, does any body have formula that accounts for prop rpm and the number of blades?

[Doug Robertson]

I'm scratching my head over this one. The rpm of the prop, whether constant speed prop or fixed pitch, versus the reciprocal speed of the camera shutter would seem to be the only factor. If the reciprocal shutter speed exactly matches or is an even divisor of the prop rpm, whether two, three, four or five blade; wouldn't that stop the prop in the photo? Most taken pictures should therefore be expected to show some prop blur. Most of mine do.

With a variable strobe light experiment, if you can match the strobe rate to the rpm of a constant rotation object, the strobe will always 'freeze' the rotating action, making it appear stopped. The only variable is to match the rotatory speed. I have done this in lab situations many times.

I set my digital camera for auto exposure in aircraft photography. The shutter speed range is 16 seconds to 1/2000th of a second. For aircraft takeoff or landing power, I normally get some prop blur but occasionally the prop appears virtually stopped. Idling props after engine start always seem to show as stopped. Whether the prop will be stopped by my camera is probably farthest from my mind. I pan the camera for most takeoffs and landings-this seems to stop the aircraft sufficiently with an automatic shutter, blurring sometimes the background.

As for geared prop aircraft engines, the Cessna 175 Skylark and the Beech Twin Bonanzas with GO engines come to mind. These engines did cost more, are more expensive to maintain and repair, and haven't proved very popular. Turboshaft prop engines are all geared way down to keep prop tip speeds in check , as well as are the Legendary Aircraft P-51 and TF-51s and other Experimental-classed aircraft that use, say, a Corvette automobile engine. Different gear ratios may be offered, dependent on the prop chosen in what are called PSRUs (propeller speed reduction units).

All this suggests to me we should just aim and shoot, hoping to catch a fast aircraft centered in the photo.
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PP ASEL

[Michael Martin]

I usually just set my shutter speed to 1/60 second and have no problem getting the blur!
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[Timothy Aanerud]

I found this tidbit in AOPA Pilot:

Getting the Shot
Advice from AOPA Pilot's senior photographer
BY MIKE FIZER (From AOPA Pilot, April 2006.)

[Doug Robertson]

Hi Timothy,
It appears from my rereading your first post question with all of Mike Fizer's AOPA article that you and he are looking for a total "disk" effect subscribed by the turning propeller in a photo rather than just "blurring" the prop, which could have a variety of perhaps random appearances, (the kind I get). Your points and MiKe Martin's along with Mike Fizer's pro advice are well taken and should do the trick, if a true "disk effect" is what you want.

Then again, some of the AOPA PILOT's cover shots in flight do not show the prop at all, OR a "disk" effect. The same April 2006 AOPA PILOT cover illustrates this on both aircraft in flight. No visible prop or prop disk. Perhaps their photo retouch lab has been at work? Contrast this with their October 2006 AOPA PILOT cover of the G36 Bonanza in flight with a total prop disk effect.

I do a lot of quick "grab" shots from the ground and never reset the shutter speed; just letting my camera set the exposure. I mainly frame the shot using the optical finder, rather than the screen, and size with the optical zoom thumb control and snap the picture, panning if necessary. My camera recycles with lithium ion rechargeable battery very quickly, allowing two to three shots of a takeoff roll or flyby, depending on my positioning. It has a "burst mode" of 5 shots also. I have taken no in-flight plane to plane shots as yet. That would require a total new set of skills and equipment, as the Mike Fizer article explains.
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[Dean Heald]

It is quite simple. (Number of Blades) * (Prop RPM / 60) will give you the denominator of the shutter speed.

For example, 2 blades, 2500RPM - The above equation gives 2 * (2500/60) = 83.33. This means that your shutter speed would have to be 1/83.33 sec or slower to get a full circle.

Another example, 3 blades, 2500RPM, requires 1/125th sec.

Dean

[Doug Robertson]

Our Aeronautical Engineer has spoken; thank you Dean.
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[Dean Heald]

Doug,

I just figured out tonight that I had to use my full name to log in. I had been using my email address as my login and had no success.

Dean

[Doug Robertson]

Great to have you onboard the Forum, Dean; we can use your learned counsel. If others have similar login or other site problems-contact Ken Wang under Contact Us. He will get a straightforward answer back to you, as the site founder and IT Specialist.
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[Airport-Data]

Welcome to the forum Dean.

Another way is to log into member section first, using email and password, then simply click on "Forums" link at the bottom, you will be logged into forum section automatically.

[Michael Martin]

[Timothy Aanerud]

You need a remote tach of course...

On take off, piston aircraft are going to be at full throttle. Unless the airplane has a very flat prop that's going to be in the 2300-2700 rpm range.

If you hear a crackling sound then it's closer to 2700 rpm. In my experience it's mostly Contenential IO-520s and IO-550's at produce the supersonic prop tip noise. A well behaved pilot will pull the power back a bit at this point.

On landing these piston engined aircraft are most likely in the 1000-1500 rpm range.