On 9/2/2010 12:15 AM rwalker spake thus:

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.

Not true.

Most (almost all?) non-electronic, mostly-mechanical cameras (35mm SLRs)
use "wide-open" viewing, so the aperture doesn't close until the shutter
is released.

Typical of this type of camera is my Minolta SRT-101, which can be used
without a battery (only powers the meter, which the camera will work
without). Twisting the aperture ring does nothing to stop down the iris,
unless the depth-of-field preview button is pushed.


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