On Wed, 01 Sep 2010 23:51:58 -0400, Attila Jozsef
wrote:

In article ,
sean-sheehan wrote:

have i managed to buy a camera with two faulty lenses or am i havin a
blonde day i have an old canon and i was trying to see if my apperture
was work on both 28 + 50 mm lenses and when i run through all the f
stops the iris dosent move. is this just me being stupid do they only
move when attached to the camera, hope someone can shed some light on
this thanks, sean

To fully answer we need to know what model camera you have, and what
type and version of lenses you have.

That being said, in general* when you "run through all the f stops" you
will not see the iris move. Most cameras are designed to communicate the
f/ stop to the body electronically, and do not physically stop down
until just before the picture is taken.

The sequence is something like: push button to take picture, iris closes
down to the indicated aperture, mirror jumps up, shutter opens, shutter
closes, mirror returns down, iris opens to maximum aperture.

Some cameras have a "depth of field preview" button or lever which stops
down the lens while you are looking through the viewfinder so you can
see and adjust the amount of depth of field the final image will have.

Hope this helps

* In the case of rangefinders such as the Leica M8, M8.2, and M9, this
does not happen since you do not see through the taking lens.


Of course, that supposes that you have a camera that communicates
electronically between the lens and the camera body. If it's old
enough that the camera doesn't need batteries (except maybe for the
meter) then the iris should stop down. But what Atilla says is
probably correct unless it is a really old camera.