Technical Lens Question

[vojm]

Just wondering (forgive me if my imagination is running wild)..Let's say I'm shooting with a 50mm 1.8 lens indoors in low light. If I were to shoot with an aperture of 2.8, does the camera open the aperture back out to 1.8 (allowing more light to come in), gain focus then shrink back to 2.8 ready for my picture?

[SwissJon]

Yes, your camera does everything at maximum aperture, and only shrinks down to the set aperture when you open the shutter or press the shutter release, or press DoF preview, therwise there wouldn't be a small enough depth of field for your camera to get an accurate focus lock.

This is why most SLR's can only AF on lenses with an aperture of f5.6 or better.

[vojm]

Originally Posted by SwissJon

Yes, your camera does everything at maximum aperture, and only shrinks down to the set aperture when you open the shutter or press the shutter release, or press DoF preview, therwise there wouldn't be a small enough depth of field for your camera to get an accurate focus lock.

This is why most SLR's can only AF on lenses with an aperture of f5.6 or better.

Wow, I felt like a light just switched on. Thanks SwissJon! I always wondered why people tell me to buy a lens with bigger aperture for low light shots (like 1.8) when I don't like the shallow depth of field of 1.8. But it makes more sense that the bigger aperture is to aid in focusing.

[3bayjunkie]

if you set your aperture you can hit the depth of field preview button to see what your photo will look like. If you don't have a depth of field preview button you can unscrew your lens by 1/4 turn without taking it off. it will then disengage the electrical contacts and show you the true DOF. so try it next time when you're out shooting!

[vojm]

Originally Posted by 3bayjunkie

if you set your aperture you can hit the depth of field preview button to see what your photo will look like. If you don't have a depth of field preview button you can unscrew your lens by 1/4 turn without taking it off. it will then disengage the electrical contacts and show you the true DOF. so try it next time when you're out shooting!

Excellent! Thanks for the tip. I think I have a DOF button, with my butter fingers, i'll probably drop the lens turning it half way, but that is a neat trick.