Archived posting to the Leica Users Group, 2010/01/30
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]* Forgive me for jumping into this exposure lag discussion late. I use the term exposure lag rather than shutter lag. Shutter lag is the elapsed time between the button press and the click of the shutter. Shutter lag is basically a function of the design and complexity of the camera. It is relatively constant depending on the mechanical and electrical activities that must take place before an exposure is made. Exposure lag includes the human reaction time between deciding to take the picture and the physical act of pressing the shutter. It is often the longest and most variable element of exposure lag.* * Human reaction time has been studied for over 200 years and was one of the first quantitative research areas in cognitive science. Simple reaction time is the time required for an individual to respond to the presence of a stimulus, i.e. to press a button as soon as an event occurs. Snapping the shutter when a batter swings at a baseball is a perfect example. The mean human simple reaction time, as measured in thousands of experiments, is approximately 180 to 200 milliseconds for a visual stimulus and 140 to 160 milliseconds for an auditory stimulus. The slightly longer time for vision is due to the more elaborate processing of visual information in the brain. The photographer is likely to snap the picture quicker if he listens for the sound of the bat hitting the ball rather than the sight of the bat hitting the ball. * * In either case the exposure lag, mechanical plus human reaction time, means that the ball will be long gone before the picture is taken. To get a picture of the batter actually hitting the ball, the photographer must decide to take the picture when the ball is halfway from the pitcher's mound to home plate. The actual picture of the batter hitting or missing then becomes a matter of luck. I apologize to the non-USA Lug members for this use of baseball examples. Substitute whatever sport you wish.* * Incidentally researchers have reported modest but statistically significant correlations between reaction time and intelligence. Although there are numerous exceptions, there is an overall tendency for individuals with a higher IQ to be slightly faster on reaction time tests. So Luggers should be the fastest of all, especially when using Leicas.* * There is a very simple non-instrumental way of measuring the time between a photographer's decision to take a picture and the camera's recording the image. Here is how to do it.* *1. Put a mark on a wall at about eye level. A piece of black tape works well.* *2. Have an assistant hold a yardstick or meter stick against the wall with the bottom level with the mark.* *3. Focus your camera with flash attached at the mark. It is best if the camera is on a tripod but it is not really necessary.* *4. Have the assistant let go of the yardstick and let it drop. It is very important that the assistant not tell you when he is going to drop it.* *5. As soon as you see the stick start to fall, press the shutter button and take a flash picture.* *6. On the viewing screen, note the number of inches or centimeters that the stick has fallen past the mark. Repeat a few times. Electrons are cheap.* * Now comes the difficult part. Using the equation for a freely falling body in earth's gravity, calculate the time elapsed for the yardstick to fall the indicated number of inches or centimeters. The equation is:* *Distance = 1/2 g x t^2* *The acceleration due to gravity in centimeters is 981 cm/sec. In inches it is 386.4 in/sec. Rewriting and simplifying the equations and solving for time, the equations are:* *for centimeters: Time = sq. rt. (D/490)* *for inches: Time = sq. rt. (D/193)* * Don't scoff at this method of measuring short times. It was used for decades in laboratories before reliable electronic instrumentation became available. With a yardstick or meter stick it works well for times shorter than half a second. Longer times let the stick fall too far. A one second interval would let the stick fall 16 feet. It might be better to drop a ball off the side of a wall. Or the Tower of Pisa.* * Here are some sample distances and times.* *Centimeters: .1 sec = 4.91 cm: .2 sec = 19.62 cm: .3 sec = 44.15 cm: .4 sec = 78.48 cm: .5 sec = 122.63 cm (beyond the length of a meter stick). Inches: .1 sec = 1.93 in: .2 sec = 7.73 in: .3 sec = 17.39 in: .4 sec = 30.91 in: .5 sec = 48.30 in (beyond the length of a yard stick).* * I cheated when I timed the exposure lag of my Oly E-500 several years ago. I simply photographed the face of a 1/100 second electric timer. An assistant started the timer. When I saw the hand start to move, I clicked the shutter. The exposure lag (reaction time plus shutter lag) varied between .35 and .45 seconds. Certainly not instantaneous. In this time a baseball thrown by a mediocre pitcher would have traveled about 3/4 of the distance from the pitcher's mound to home plate. Three examples of this measurement of exposure lag are:* * * ** * http://gallery.leica-users.org/v/Larry+Z/Timer_+flash.jpg.html http://gallery.leica-users.org/v/Larry+Z/Timer_+bright+room+light.jpg.html http://gallery.leica-users.org/v/Larry+Z/Timer_+ambient+room+light.jpg.html * * * * Incidentally the camera I own with the shortest exposure lag is a Rollei 35S. Even faster than a Leica M3.* ** *Larry Z* * *