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Why do smaller apertures (larger f-stops) have shorter available shutter times?

At f2.8 (the largest available aperture) the minimum shutter time is 1/1000 second. At f8.0 (the smallest available aperture) the minimum shutter time is 1/2000 second. Doug Wilcox has a possible explanation...

Doug Wilcox (alternate photo-gallery) (Yahoo!, Panasonic forum, 9th April 2004)...

The shutter is actually the aperture blades. What this means is that the shutter only opens to the assigned aperture. If the aperture is f2.8 then the shutter has to make a full travel, which takes more time than shooting at f8 which means the shutter only opens a short distance and then closes. The difference in travel accounts for the fact that we can get higher shutter speeds at smaller lens openings.

...But except when using shutter speeds to stop action, you will most need the faster speeds when the lighting is really bright and you need to limit it {and so you will probably be using the smallest available aperture i.e. f8}. Therefore if f8 and 1/1000 will not do it having the extra stop to 1/2000 might be handy.

{Picture below `Reflections' by Doug Wilcox. Taken with FZ10}

Reflections. Taken with FZ10

However, some people have noted that the shutter appears to be closing behind the aperture blades (Mike Curtis `medic1210' in dpreview, Panasonic forum, 27 February 2005)...

if you set a mid-point aperture like 4.5 or 5.6 you can clearly see the aperture blades in their set position. When you take a pic, you can see the `shutter' close behind the aperture blades after the exposure is taken...

The way I can tell that the shutter is closing behind the aperture blades, and is therefore completely independent of the aperture blades is because if you leave the aperture at f/2.8 and shoot an exposure for say a second or more, you can easily see the shutter when it closes. The way you can tell that it's not the aperture is because it is just a flat piece of something instead of being made up of 6 separate blades. This is also easily evident if you zoom in to 12x and set a mid-point aperture like 4.5 or 5.6. When you half press the shutter release, you will see the blades stop down. If you then take the picture, you will see that the blades remain in this stopped down position when the `shutter' closes behind them.

Colorful Jacks. Taken with FZ20

(`Colorful Jacks', POTD winner taken by Mike Curtis with a Panasonic FZ-20)


next up previous index Link to 'photography' page
Next: What is the FZ10 Up: Specifications Previous: Minimum focus distance   Index
David Fong 2009-09-04