[Leica] Measuring exposure lag (a long post)

[henningw at archiphoto.com (Henning Wulff)]

Larry, you can measure 'exposure lag' in a lot of different ways. 
Each way can simulate a different condition that  may arise.

Photographically, 'exposure lag' will vary a lot depending on the 
type of photography that you are doing.

If you are in a blind, and want to catch a bird just as it appears at 
the opening of its next in the trunk of a tree, your example might 
apply. Please note 'might'. It would apply if the bird will appear in 
the next 5 to 30 seconds. If it is likely to appear within 4 to 5 
hours, your reaction time will be longer, and the lag will suffer. 
Sometimes my exposure lag is a couple of minutes, because I will see 
a picture, slam on the brakes, back up and stop, jump out of the car, 
jump back in to get the camera gear I want, put the right lens on the 
camera and then run around the car to see the picture and take it.

As you noted, to get a picture of the ball hitting the bat, 
anticipation is necessary as well as experience with baseball and 
with your camera and how you interact with it. With practice, it's 
quite possible to get your picture within the correct 20 or 30 
milliseconds 75% or the time or better.

The shorter the camera's shutter lag time, the easier it is to get to 
that point of familiarity. When you are very familiar with your 
camera, have taken tens of thousands of frames, lag time becomes a 
non-issue as you have learned when to start the process of initiating 
the process of taking a picture to get the picture when you want. 
This is assuming you are also familiar with your subject matter. HCB 
knew his subject matter, and could have gotten that puddle jumper 
with a camera that had 250ms shutter lag, as long as he would have 
had enough frames through it to know the camera.

Problems come up when you use a couple of different cameras, or when 
you use autofocus, especially when you use autofocus in focus 
priority. Then that experience doesn't kick in correctly, and then a 
short lag camera will give you a better chance of getting the shot 
than a long lag camera.

As for the Rollei 35, it as well as most other between the lens 
shuttered cameras can be very quick; the quickest being those that 
have a soft, short travel shutter release on the lens itself. The 
Rollei has the problem that it doesn't have the smoothest release, so 
it's not always as predictable as one would like. Not like an SWC, 
but still not that smooth.




>* 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*
>*
>*
>
>_______________________________________________
>Leica Users Group.
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    *            Henning J. Wulff
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