f2.8 against f4.5

[Cutter]

Hi everyone I know quite alot as been said on the matter of fast glas f2.8 and my canon f4.5 but i would like to know one last thing (and forgive me if this is a daft question) ok if we were taking a picture with both lenses and the light was very good to acheive a fast shutter speed which one would take the best picture? or are we just talking about the f2.8 can shoot in lower light situations?

Ps both lenses canon and L series

[chris-p]

Better in what way?!

If you're shooting wide open on both lenses then the f/2.8 should still be better as the glass should be better quality. If you're shooting at f/4.5 on both lenses the f/2.8 will definitely be sharper as it's not wide open but the f/4.5 is.

[cosmicma]

Originally Posted by chris-p

Better in what way?!

If you're shooting wide open on both lenses then the f/2.8 should still be better as the glass should be better quality. If you're shooting at f/4.5 on both lenses the f/2.8 will definitely be sharper as it's not wide open but the f/4.5 is.

thats a very good answer and just about sums it up without putting a lab coat on ( getting technical )

[flake]

This is another question which is impossible to answer! Firstly you haven't specified an aperture, if you take it at f/4.5 (which is not a proper stop) then the f/2.8 should theoretically take a better shot because lenses generally perform better stopped down a little. However if you change the aperture to f/8 the story might be very different.

Canon cameras have a more sensitive centre focus sensor which is only active when a lens of f/2.8 or wider is used, so the faster lenses focus more quickly and more accurately.

Aperture is not a guide to the optical quality of a lens in any way.

[Cutter]

Originally Posted by chris-p

Better in what way?!

If you're shooting wide open on both lenses then the f/2.8 should still be better as the glass should be better quality. If you're shooting at f/4.5 on both lenses the f/2.8 will definitely be sharper as it's not wide open but the f/4.5 is.

Thanks Chris thats the answer I was looking for ie: if both lenses were set ok(flake F5.6) then the f2.8 lense would be sharper photos

[flake]

Originally Posted by Cutter

Thanks Chris thats the answer I was looking for ie: if both lenses were set ok(flake F5.6) then the f2.8 lense would be sharper photos

Unfortunately that is not right! It's all down to the design of the lens, and the modern computer designed lenses are going to be sharper than older designs regardless of aperture. The measurement which affects this is generally resolution, and to a lesser extent contrast. As an example the Canon 28mm f/1.8 at f/5.6 shows centre res of 2084 Line pairs and a border of 1590 the 24 - 105mm f/4 IS L at f/5.6 centre 2023 border 1804.

This shows that although both lenses show similar centre performance, the border performance of the f/4 is markedly better despite the fact it's competitor is a fast prime lens.

If you really want to acheive the sharpest possible images then technique is more important than the glass, so you really need to use a tripod with remote release and mirror lock up. Even then to get the ultimate performance a shutter speed of over 1/500 sec (Not possible using flash).

[Cutter]

Originally Posted by flake

Unfortunately that is not right! It's all down to the design of the lens, and the modern computer designed lenses are going to be sharper than older designs regardless of aperture. The measurement which affects this is generally resolution, and to a lesser extent contrast. As an example the Canon 28mm f/1.8 at f/5.6 shows centre res of 2084 Line pairs and a border of 1590 the 24 - 105mm f/4 IS L at f/5.6 centre 2023 border 1804.

This shows that although both lenses show similar centre performance, the border performance of the f/4 is markedly better despite the fact it's competitor is a fast prime lens.

If you really want to acheive the sharpest possible images then technique is more important than the glass, so you really need to use a tripod with remote release and mirror lock up. Even then to get the ultimate performance a shutter speed of over 1/500 sec (Not possible using flash).

Thanks Flake you are obviously very knowledgable on the subject and i bow to your experteese, you see I am a beginner and I am trying to find out (as you say) whether it the lense thats the big factor or my shooting technique. I think from what you have written its prob my technique. I will if poss send you a couple of pics so you can see or in fact tell me what you think my problem is.

ps what remote release would you recommend?
Cheers

[flake]

Ah if only it were so easy to tell by looking at images what the problems might be. Exif data is the best clue as it gives all the camera settings, but remember that no one gets it right all the time, and even the definitions of 'right' are different to each photographer.

I prefer the wired remotes, and Canons own are not too expensive, third party ones do just as well too. Wireless controls are preferred by others, but I don't like the fact that there is a blind spot where the sensor can't see the remote, and the sensor is on the front of the camera.

[chris-p]

Another vote for wired remotes here.

[cosmicma]

i use a canon wired remote on the canon 40d and 50d ( same remote ) but am thinking of going wireless it won't be the genuine canon one that costs the a fortune it will be a third party RF rather than infra red type
gonna have a bit of a read on whats reccomended

the wired remote works flawlessly but i'm tired of the lead tangleing round everything