would it be bad (f/2.8 Vs. f/4 zoom lenses?)

they can do anything that a f4 can do and more right?

Photolistic wrote in post #2064685
they can do anything that a f4 can do and more right?

No it wouldn't be bad (in many circumstances it's preferred).
Yes, they can do anything the others can do...including serious drainage on your wallet

Basically, you are right.

But:

1) f/2.8 is sometimes not enough. You need faster apertures for special effects and in bad light conditions.
2) there are also disadvantages: f/2.8 lenses are more expensive and heavier (compare 70-200 f/4 and f/2.8 -> f/4 is far more suited when taking photos in an animal park, for example)
3) not all lenses are sharp wide open, thereby limiting the usefulness of wide apertures.

Other than that, speed is your friend.

P.

peterdoomen wrote in post #2064701
speed is your friend.

P.

I like that Peter...when I switch my signature, that's going on there

f/1.4 > f/1.8 > f/2.8 > f/4

'nuff said.

As Peter has already pointed out, the only things preventing everyone from owning f/2.8 zooms is the cost and weight of these lenses.

Yes,
1. a f2.8 lens will provide a brighter viewfinder image, very important when shooting in the dark.
2. On some cameras, a lens f2.8 or faster will focus faster than a slower lens.
3. You can double the shutter speed over an f4
4. More shallower DOF.
5. Most lenses are sharpest about a couple stops from wide open, so for a f2.8 lens, that's f5.6. For a f4 lens that f8 (which maybe too slow)

thanks 70-200 2.8 is for me then. Just cant decide. canon 70-200 2.8 IS or sigma 70-200 2.8 macro and another lens

Photolistic wrote in post #2064724
thanks 70-200 2.8 is for me then. Just cant decide. canon 70-200 2.8 IS or sigma 70-200 2.8 macro and another lens

The canon, for sure. Even the 2.8 non IS.

SimonG wrote in post #2064713
As Peter has already pointed out, the only things preventing everyone from owning f/2.8 zooms is the cost and weight of these lenses.

I would say weight is more significant than cost.

You only pay for the lens once, but you pay for the weight every time you take it with you.

Looks like the statement should be:

buy all 2.8 lenses or faster...............

Buy lenses that are realistic for your needs. The 300mm f/2.8 L IS is one of the most awesome lenses on the face of the planet...lightning fast focus, great performance in low light and out of this world image quality... It also costs around 4 grand here in the states. Unless you are a lottery winner or you have a job that justifies owning this lens....that is a whole lot of money to just be sitting in your closet 364 days out of the year.

It makes way more sense to identify what your shooting needs are...and purchase lenses accordingly. Nothing wrong with having an f/4 lens for a daily shooter...and if the situation comes about that you think you need some super fast or super wide or super long glass...you can always rent it...there are tons of rental places today and even more coming up all the time. Rental rates sure beat making payments or eating Ramen for a year or two. Most situations that we find we need fast glass for come with a bit of warning....weddings or sports events are scheduled for some time in advance...so renting isn't that hard to arrange.

Would it be safe to say, a 2.8 will achieve its "sweet spot" faster than a f4?

it's hard to say, alot of f/4 lenses are very good from wide open, so are alot of 2.8 lenses, the 300 2.8 IS pretty much gets to maximum resolution by about 4, but it is not soft at 2.8, you would have to compare both images @100% to notice the slight increase of resolution.

bangarang wrote in post #2064841
Would it be safe to say, a 2.8 will achieve its "sweet spot" faster than a f4?

not necissaraly faster, but at a lower av value. most lenses are just about as sharp as they will get between two stops and f11. on a 1.8 lens, that is f3.5, on a 2.8, that's F5.6. both are two stops in from wide open, but the 1.8 is still 1.3 stops ahead.