> TB wrote:

>> Actually, it is do do with shutter speeds. Modern video cameras have
>> electronic shutters. They are used to avoid the blurring effect often
>> associated with video cameras and slow motion effects. If the shutter
>> speed wasn't set high the propellor blades would be seen as a blur. I
>> prefer to set the shutter slower for these types of shots.

>
> You have avoided the OP's actual question.
>
> In a still photo or a single frame of a motion picture, use of a
> higher shutter speed reduces the blurring of the image of a moving
> object--whether the shutter is mechanical or electronic or solid
> state--and the enhanced sharpness of the moving object's image can be
> a desirable effect.
>
> However, when viewing a moving picture, the apparent change in the
> rotational speed or direction of a prop blade is a product of the
> strobe effect (the relationship of the frame rate to the rotational
> rate), and can only be demonstrated in viewing the "moving" images.
>
> Setting the shutter speed to the slowest practical speed will tend to
> show the propeller as a translucent disk, in viewing the still frame
> and in viewing motion, and tends to minimize the perceived strobe
> effect due to the increasingly undefined image of the prop blade with
> slower shutter speeds, but does _not_ deal directly with the cause of
> the strobe effect.
>
> Control of the strobe effect can be demonstrated easily at home using
> a portable fan with variable speed control and a light source powered
> by 50- or 60-cycle A/C power.
>
> This same effect is often seen in TV ads for automobiles, or in
> movies, with the wheels of a moving auto apparently turning in the
> "wrong" direction. As the auto changes speed the wheels sometimes seem
> to change their direction of rotation. The rate of rotation has
> changed but the camera's frame rate has not--thus the relationship
> between the two rates has changed enough that the visual effect is one
> of a directional change in the rotation of the wheels of the automobile.
>
> A picture is worth a thousand posts (watch all of it):
> http://www.youtube.com/watch?v=zr5Ip5hHVik
>
>
>
>
> Jack
>
> ---------------
>
>

>> "J a c k" yahoo.com> wrote in message
>> news:K8Msi.31248$2v1.14761@newssvr14.news.prodigy.net...

>>> TacAN wrote:
>>>

>>>> I'm intrigued by the illusion of the engines running backward - perhaps
>>>> some of the photographers in this group can explain what causes this
>>>> effect.

>>> Interaction between frame rate of the camera and rotation speed of the
>>> prop. Reminiscent of way we used to set the timing on an auto engine
>>> with a strobe light.
>>>
>>> Intervals are usually around 30 frames sec. for normal motion: not to be
>>> confused with shutter speeds, which for still or motion can be from
>>> 1/60th sec. on up for handheld cameras, depending on the speed (light
>>> sensitivity) of the film.
>>>
>>> More than you wanted to know. Theses days we just point and shoot.
>>>
>>>
>>> Jack

>>
>>

>