Is This In Fact True? (Page 5): Some are mixing up relative depth of field with f-stop. Don't worry; your f2.8 lense is still f2.8. Of course if you think it really has changed, sent...

wdross Loc: Castle Rock, Colorado

Cdouthitt wrote:

Then why is it that often times someone will say that my f2.8 lens (m4/3) is actually an f4 lens on FF?

Some are mixing up relative depth of field with f-stop. Don't worry; your f2.8 lense is still f2.8. Of course if you think it really has changed, sent that "f4 defective" f2.8 lense to me. I'll try it on my Olympus for a year and see if I can get it to go back to f2.8 from that "f4".

Cdouthitt Loc: Traverse City, MI

wdross wrote:

Some are mixing up relative depth of field with f-stop. Don't worry; your f2.8 lense is still f2.8. Of course if you think it really has changed, sent that "f4 defective" f2.8 lense to me. I'll try it on my Olympus for a year and see if I can get it to go back to f2.8 from that "f4".

Nope, no issues at all here...I think I'll keep em.

BebuLamar

rmalarz wrote:

Bebu, It doesn't matter where the lens aperture is. Whether it is in the lens, in front of the lens, or behind the lens, ultimately the somewhere between optical center of the lens and the focal plane there is going to be a determining aperture. So, it's still a ration involving lens focal length and lens opening.
--Bob

You wouldn't understand what he said. He said if you remove the lens from the camera it's an f/1.8 lens because it is. When you attach the lens to the camera it's only f/2.8 because the built in diaphram in the camera mask the lens down to f/2.8 max that is when it's open all the way it still mask some of the lens opening.
But this is not an exception to the rule. Basically if you take a lens and put a mask in it you make it a slower lens. And this is the case. Not an exception.

rmalarz Loc: Tempe, Arizona

Well, your explanation goes right back to the formula. By putting a 'mask' on the lens, you've effectively changed it's diameter. Thus, the change in f-stop values. It's not necessarily the diameter of the lens, but the opening of the lens, or effective diameter. So for that camera application, the lens is a 2.8 lens.
--Bob

BebuLamar wrote:

You wouldn't understand what he said. He said if you remove the lens from the camera it's an f/1.8 lens because it is. When you attach the lens to the camera it's only f/2.8 because the built in diaphram in the camera mask the lens down to f/2.8 max that is when it's open all the way it still mask some of the lens opening.
But this is not an exception to the rule. Basically if you take a lens and put a mask in it you make it a slower lens. And this is the case. Not an exception.

mchroust Loc: McMinnville, Oregon

Have you guys ever heard that light that comes through the optics of the lens is lighter in the center of the lens and the light falls off as it reaches the edge of the lens. if your aperture is larger than the sensor, than the center (brightest) light would hit the sensor and the edge (darker) light would miss the sensor.

rmalarz Loc: Tempe, Arizona

That must be what causes the, what appears to be, dust on the inside of my cameras. Light that fallen off the edge of the lens. Perhaps, if I put duct tape around the edges, it'll keep the light from falling off. Can never tell.
--Bob

mchroust wrote:

Have you guys ever heard that light that comes through the optics of the lens is lighter in the center of the lens and the light falls off as it reaches the edge of the lens. if your aperture is larger than the sensor, than the center (brightest) light would hit the sensor and the edge (darker) light would miss the sensor.

wj cody Loc: springfield illinois

rmalarz wrote:

That must be what causes the, what appears to be, dust on the inside of my cameras. Light that fallen off the edge of the lens. Perhaps, if I put duct tape around the edges, it'll keep the light from falling off. Can never tell.
--Bob

ooh, Bob, nasty boy! you know, black electricians tape adheres much better to the front element!