I'm a bit more than a bit bored with calibrating tractors. I am not an expert with digital imaging, but I know a little bit more about engineering, so thought I would explain in diagramatic terms how the shutter works on your camera. 1st Diagram - shows the shutter at rest with no light getting through to the sensor. 2nd Diagram - as the shutter fires the 1st curtain begins to open and allows light through. 3rd Diagram - 2nd curtain begins to close shutting off light to the top part of the sensor, 1st curtain is open enough to allow light to the middle of the sensor . 4th Diagram - 1st curtain is fully open allowing light to bottom of the sensor, 2nd curtain is blocking light to middle of the sensor. 5th Diagram - 1st curtain begins to close blocking light to the sensor and they both return to rest position. All this happens very quickly sometimes fractions of a second. As you can see the light from the lens actually travels across the sensor (or film) in a horizontal band that moves down, not all the sensor (film) is exposed to the light at anytime. Two curtains are necessary because it would be physicaly impossible to get one to open and shut quick enough for modern cameras. In real life the curtains are made of very fine leaves of material, often metal, in some high end cameras of carbon fibre composite. They are controlled by tiny magnetic pulses which will open and close them very quickly.

And every one said, 'If we only live,
We too will go to sea in a Sieve,---
To the hills of the Chankly Bore!'
Far and few, far and few, Are the lands where the Jumblies live;
Their heads are green, and their hands are blue, And they went to sea in a Sieve.

Edward Lear
http://www.nonsenselit.org/Lear/ns/jumblies.html

If you are using a through the lens metered flash you can set the flash to fire either when the 1st curtain opens or when the 2nd curtain opens. Since the shutter will stay open until the sensor has sufficient light if you set it to fire with the first curtain, the 2nd curtain will close almost intaneously giving a sharp image. If you set it to fire as 2nd curtain the 1st curtain will open allowing light to the sensor, the flash will fire, the 2nd curtain will then operate. This gives a double image one for the first curtain opening and one for when the flash fired.

And every one said, 'If we only live,
We too will go to sea in a Sieve,---
To the hills of the Chankly Bore!'
Far and few, far and few, Are the lands where the Jumblies live;
Their heads are green, and their hands are blue, And they went to sea in a Sieve.

Edward Lear
http://www.nonsenselit.org/Lear/ns/jumblies.html

ok - I have now learned how to spell instantaneously.

The above illustration is for a focal plane shutter, which is the most common type in use. By having a band of light crossing the sensor or film a very even exposure can be obtained, which would not be possible if all the sensor was exposed at once. For long shutter speeds the band is wide, for shorter shutter speeds the band gets narrower.

Message edited on: 05/17/2005 05:19

And every one said, 'If we only live,
We too will go to sea in a Sieve,---
To the hills of the Chankly Bore!'
Far and few, far and few, Are the lands where the Jumblies live;
Their heads are green, and their hands are blue, And they went to sea in a Sieve.

Edward Lear
http://www.nonsenselit.org/Lear/ns/jumblies.html

Richard this is awesome! Thank you.....

I am, therefore I create.......
--- michelleamarante.com

I second that! thanks Richard

WOW!! Thx for that Rich!!! It's clear and so easy to understand!!! U rock! Yep! ;D

Rich, very interesting and informative. I appreciate the info.

Kort Kramer - Kramer Kreations

here, here!! thank you Richard :]

Fascinating stuff...thanks for posting. -Jeff :-)

HH.great explanations and diagrams! Thank,s a lot for that!

Excellent explanation! Further to this, please note that some DSLR's use a combination of mechanical and "electronic" shutter. For example ,the D70 I believe uses an electronic shutter for speeds faster than 1/250 second...mechanical for speeds lower than that. My understanding is that the electronic shutter is really only the time the sensor is "hot" and can accept data.

In youth, we learn....with age, we understand.

you make it look simple, Richard. i don't understand metered flash. my manual doesn't mention it. i'll study this sometime. i'd like to learn more about it. thanks for doing this!