what does f/2.8 mean?

[Martin Eager]

http://www.dpreview.com/learn/?/Glossary/Exposure/Aperture_01.htm

 

[Shih-Hsung Hwu]

I am confusing what dose f/2.8 - f/3.5 means? And How do I know how fast is a paticular lense? I hear lots of people saying your lense is not fast enough to use under low light or sports enviroment. Could anyone help me to clearfy this technical problem? Thanks in Advance!!

Alex

 

[Ryoohki]

The F is the size of the Opening that can get light thru the lens to the sensor.

The Smaller the F is, the larger it open thus good for low light. Small F with good glass cost more than standard 3.5/5.6 ones.

The more light get in, the better it is for the camera speed so it's faster.

I am confusing what dose f/2.8 - f/3.5 means? And How do I know how
fast is a paticular lense? I hear lots of people saying your lense
is not fast enough to use under low light or sports enviroment.
Could anyone help me to clearfy this technical problem? Thanks in
Advance!!

Alex

--

Cameranumerique.net (Forum Québécois de caméras Numériques) http://www.cameranumerique.net

 

[Freeman-Jo]

While you are there, look up depth of field too, it goes together. And probably make you understand better.
http://www.dpreview.com/learn/?/Glossary/Optical/Depth_of_field_01.htm

http://www.dpreview.com/learn/?/Glossary/Exposure/Aperture_01.htm

--
I love Michelle Kwan

 

[Povl H. Pedersen]

I am confusing what dose f/2.8 - f/3.5 means? And How do I know how
fast is a paticular lense? I hear lots of people saying your lense
is not fast enough to use under low light or sports enviroment.
Could anyone help me to clearfy this technical problem? Thanks in
Advance!!

Alex

 

[Freeman-Jo]

I am confusing what dose f/2.8 - f/3.5 means? And How do I know how
fast is a paticular lense? I hear lots of people saying your lense
is not fast enough to use under low light or sports enviroment.
Could anyone help me to clearfy this technical problem? Thanks in
Advance!!

Alex

--
I love Michelle Kwan

 

[Doug Kerr]

Alex,

I am confusing what dose f/2.8 - f/3.5 means? And How do I know how
fast is a paticular lense? I hear lots of people saying your lense
is not fast enough to use under low light or sports enviroment.
Could anyone help me to clearfy this technical problem? Thanks in
Advance!!

f/2.8 means that the effective diameter of the aperture is the focal length of the lens divided by 2.8. If we set aside a couple of small wrinkles, it tells us the "light-gatherng power" of the lens. The smaller the f/number, the larger the aperture (and the greater the light-gathering power).

Leneses with larger apertures are often spoken of as "faster", since the larger aperture allows proper exposure to be achieved with a shroter exposure (faster shutter speed).

When the description of a zoom lens includes two f/ numbers (such as 28-105 mm F/3.5-4.5), it means that at teh wide angle end of the focal length range, the aperture is f/3.5, while at the telephoto end, it is f/4.5.

Best regards,

Doug