Archived posting to the Leica Users Group, 2003/08/08

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Subject: [Leica] More on lag measurement
From: LRZeitlin@aol.com
Date: Fri, 8 Aug 2003 19:07:25 EDT

You don't even have to use film. The flash will illuminate the position of 
the marble and you or your friend will be able to mark how far it has dropped on 
the meter stick. Repeat the test a number of times and discard all readings 
less than 15 cm. You are obviously jumping the gun. This simple test is about 
as accurate as they come.

Larry wrote:

<<Here is how to measure your own total lag time (human plus camera). Set up 
a meterstick against a wall. Have a friend hold a small object, say a black 
marble, at the top of the meterstick. Focus your flash equipped camera on the 
stick. Now tell your friend to drop the marble at any time during the next few 
seconds but not to give you any indication of when it will be dropped. When you 
see the marble start to move, snap the shutter. Repeat the process at least 
half a dozen times.

Now look at the prints (or just the negatives through a magnifying glass). 
Using the equations we learned in high school physics we know that the distance 
the ball will fall in a given time is:

distance = 1/2 a  * t^2

where distance is measured in centimeters, 
a is the acceleration due to gravity and is equal to 980 cm/sec/sec
t is time in seconds.

This equation can be rewritten as:     time = sq. rt. (distance/490)

If the average distance the ball travels is 20 cm, the total latency is 202 
milliseconds.
If the average distance is 30 cm, the latency is 247 milliseconds
If the distance is 40 cm, the latency 286 milliseconds
And 50 cm = 319 ms.; 60 cm = 350 ms.; 70 cm = 378 ms.; 80 cm = 404 ms.; 90 cm 
= 429 ms.; 100 cm = 452 ms.

If the ball bounces off the floor before the camera clicks, either get a new 
camera or forgoe sports photography. You will miss too many pictures.>>
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Replies: Reply from frank theriault <knarf.theriault@sympatico.ca> (Re: [Leica] More on lag measurement)