f/4 lens and f/2.8 lens equal ?

[LowLights]

wow, wonderful sweeping statement, first i heard f4 and f2.8 lenses are on par.
well done, all my L lenses are a waste of money.

tomorrow shall tell all my colleagues not to waste money.... its all the same...

:bsmilie: :bsmilie: no lah.. the f stop on par will not devalue your L lenses.. I am looking at it from a different angle, one that is more from a pratical point of view rather than a equipment point of view..

.. of course the f2.8 has it advantages.. hence the cost.. :sweat:

and do stop your colleagues from buying.. Canon will come after me ...:bsmilie:

 

[raptor84]

70-200 f/4 and 2.8 are very sharp wide open. I have a f/4 and love it.

 

[LowLights]

Yes, the cam always AF at the widest aperture. As a result, the f/2.8 will have an edge over the f/4 in this area, regardless of whether you stop to f/8 or not.

Regards,
JK

Thanks

 

[LowLights]

When focusing the aperture defaults to its widest for the sensor to work accurately. When you trip the shutter the lens blades go to their intended aperture and the film/sensor is exposed. That is why when you hold down the depth of field preview button on your camera the image darkens a little. That's actually how much light is coming through at the set aperture.

Ok.. so the blade of the aperature stays at its widest (f2.8).. until tiggered,, then it will size the aperature to our setting size (say f8).. rite ?

 

[calebk]

Ok.. so the blade of the aperature stays at its widest (f2.8).. until tiggered,, then it will size the aperature to our setting size (say f8).. rite ?

Spot on.

 

[LowLights]

Spot on.

Great .. thanks..

 

[Snoweagle]

But after using my 17-40, i really find that f/4 is sufficient.

 

[LowLights]

But after using my 17-40, i really find that f/4 is sufficient.

LOL .. me too.. hence the thread to reconfirm some of my thought.. but from the replies it clear that f2.8 will focus faster.. but hey f4 does not slow either just one stop ...

 

[unseen]

But after using my 17-40, i really find that f/4 is sufficient.

Look at it this way, you haven't used a F2.8 lens long enough to realise how inadequate F4 is.

Most F2.8 photogs wouldn't ever want to switch to a F4 lens. They call it a downgrade, not a "change".

That said, i don't believe you shoot a wide enough variety to be able to justify your statement. A pure landscape photographer would find F/8 enough, an actual event photographer (not those odd job photographers) would find F2.8 not enough sometimes.

 

[unseen]

2 lenses - one f/4, the other f/2.8
If constrain to the following ....
1) Low Lights conditions
2) Aperature f/8
3) ISO set to 1600
4) Shutter Speed 1/60
5) IQ, build of the 2 lenses are ignore for this case as not to complicate matters. Let's assume they are identical except for the f-stop.
6) No flash

Are they then identical in proformance ?
Or should I say that the F/2.8 lens does not have an advantage over the f/4 lens in this case.

So gentlemen.. would it make the f/4 lens less worthy than the f/2.8 lens in such a situation ??

If you were to ignore the IQ.. Then what performance are you talking about?
Focusing? Answered by others.
Other than that.. what else can be compared?

Let's broaden your question to show how absurd the topic may be.
Suppose your conditions hold for 4 lenses now.. Max apertures of F2.8, F4, F5.6, F6.3
Given that apart from focusing being slow or less accurate... There's nothing else to separate the 4 of them. So if you would conclude, a F6.3 lens is good enough?

For most people however, the ability to gain 1 stop is much much desired. Imagine at your setting, the subject starts to move. Would you want to stick at 1/60 and get all motion blurred images to maintain the proper depth of field, or would you sacrifice 1 stop worth of depth of field, in exchange for sharp images @ 1/120?

You should never under-estimate the 1 stop gain.

 

[calebk]

Look at it this way, you haven't used a F2.8 lens long enough to realise how inadequate F4 is.

Most F2.8 photogs wouldn't ever want to switch to a F4 lens. They call it a downgrade, not a "change".

That said, i don't believe you shoot a wide enough variety to be able to justify your statement. A pure landscape photographer would find F/8 enough, an actual event photographer (not those odd job photographers) would find F2.8 not enough sometimes.

Most of us, as hobbyists, don't have that privelege (of using f/2.8 lenses for long periods of time). Of course there are exceptions and I know a few lah. :bsmilie:

 

[Snoweagle]

I've used both 70-200 f/4 and f/2.8 and i think both AF just as fast, not much of a diff. f/2.8 is just an extra stop of light better, else it's the same.

 

[zekai]

professionally, 1 stop is a lot.

though professional studio work normally use f8 - f22.
professional event work utilises f 2.8 very often.

if you do not need it, you do not need it. Do not have to state in the forum they are both as good, because they are very different.

 

[Snoweagle]

professionally, 1 stop is a lot.

though professional studio work normally use f8 - f22.
professional event work utilises f 2.8 very often.

if you do not need it, you do not need it. Do not have to state in the forum they are both as good, because they are very different.

Well today i took and indoor event at f/4, ISO 400 and with flash. Shutter speed around 1/60 - 1/80 and the results are very gd and also bright. So i stopped down to f/5.6 and results are better.

 

[paisatge]

Look at it this way, you haven't used a F2.8 lens long enough to realise how inadequate F4 is.

Most F2.8 photogs wouldn't ever want to switch to a F4 lens. They call it a downgrade, not a "change".

That said, i don't believe you shoot a wide enough variety to be able to justify your statement. A pure landscape photographer would find F/8 enough, an actual event photographer (not those odd job photographers) would find F2.8 not enough sometimes.

Reminds me how I used to think people spending 2x more for the 16-35 f2.8 than the 17-40 f4 were crazy. After using a 50 f1.4 myself, I've basically chucked all the zooms away and now 99% using fast L primes. The DoF control and bright viewfinder and IQ are simply satisfying. ;p

However, slow lenses like f4 have the advantage of being lighter. So, whenever I go for a long trek, f4 lenses would be the first choice. Not to mention that during trekking, I don't normally need a fast lens as I would be mostly shooting landscape stuff with a great DoF.

 

[Snoweagle]

f/4 lens aren't slow.

 

[zekai]

f/4 lens aren't slow.

well it is slower than f2.8

 

[Snoweagle]

well it is slower than f2.8

Very slight only, almost negligible.

 

[zekai]

Very slight only, almost negligible.

1 stop of light difference is not negligible.

 

[ExplorerZ]

Very slight only, almost negligible.

you muz be kidding if you say negligible... its a different between shooting 1/100 and 1/200 on a tele lens (assuming you are at your max ISO) it simply give you far far higher chance to get sharp shot on the tele side (200mm in this case)