Question about speed of Fast lens vs normal one

[Michael Ang]

hi,

just curious...

if i have 2 lens, one say EF 70-200 L F4 and another say EF 100-300 normal lens....

in the same outdoor lighting condition aimed at the same subject , and say i set my camera to AP at F11 and use the same focal length say at 100mm....

would the speed reading Tv be the same ? eg at 1/500?

or would the faster lens F4 one be showing a faster speed as compared to the other len?

just wondering what advantage would i have if I bought a fast len 70-200 F4 if I am going to use it at a higher F no...... :lovegrin: actually trying to talk myself out of getting one

Thanks...

 

[mpenza]

The Tv will be the same if the aperture is set the same. it depends on the aperture you're using, not the largest aperture of the lens.

 

[malek]

just wondering what advantage would i have if I bought a fast len 70-200 F4 if I am going to use it at a higher F no......

usually fast lens come with small apature number, like f2.8, which then have bigger apature opening...
advantage is... at this biggest opening, you can have shorter shutter speed.. so have a possibilities to handheld your camera while shootin'

but u usually need very2 big money for this small f number

 

[ST1100]

Faster lenses also equate to brighter viewfinder and for some camera bodies, faster AF using cross sensors.

Faster lenses also imply (but not necc always true) better optics and better build, faster AF (lens motor), and better features like weather sealing, nonrotating front element and non-extending zoom. Depends on the specific lens models you are comparing.

 

[ST1100]

If you're at the point of talking yourself out of it, you may be past the point of no return already.

 

[Michael Ang]

hi guys,

thanks for the reply...

okie...so faster lens doens't equal to a faster Tv.... if the apeture is the same... advantage is the ability to set to a faster appeture while in a long focal length...

ST1000, you are almost right... been tempted to get the EF 70-200 F4 for a long time now.... been able to resist it so far... may the force be with me.. hahaha....

 

[justdoit]

Fast lens usually comes with better optical quality.
Let's say for Canon, most L lenses' are fast lenses that have smallest aperture of 2.8 or 4.
The problem is, you have to buy the "fast" and "L" together.