Canon Zoom F4 F2.8

[Woodward]

There's a huge difference in price between Canon Zooms F4 F2.8, is a F4 ok in good light? Would it be as sharp as a F2.8?

[ricktas]

There's a huge difference in price between Canon Zooms F4 F2.8, is a F4 ok in good light? Would it be as sharp as a F2.8?

Most lenses are not as sharp at either end of their aperture range. Most lenses are their sharpest when set to between f8 and f14.

Also every single lens is going to have its own quirks. You could put 10 copies of the same lens side by side and each will have its own small discrepancies.

What are you wanting to shoot with the lens?

[Brian500au]

I have owned both twice - they are different lenses for different reasons. There is no difference is sharpness between the IS version of either one of them. The difference is weight and the max aperture. You decide what you main purpose of the lens and then you will get more specific advice.

[I Like to Watch]

Assuming we are talking about the 70-200mm zoom ?

As others have mentioned, if you 'Stop down' from maximum aperture, you will probably get a much sharper image from both lenses.
(which means f/4 on the f/2.8 will be sharper than f/4 on the f/4 lens).

However, you will never have f/2.8 available on the f/4 lens. The 'faster' lens will also mean bigger and heavier to carry though. When I had this choice many years ago, I got the f/2.8 because I wanted it for sport shots.
That may not be the right choice for you though.

[Tannin]

Actually, with the Canon 70-200s, the sharpness difference between wide open and a stop or two down is trivially small. For not-quite-all practical purposes, it doesn't exist. The general rule is that lenses are sharpest in the middle of their range, but really good quality lenses go a long way towards breaking this rule. Wide-open sharpness is one of the reasons (perhaps the main reason) why people pay $2000 for a particular lens when another fairly similar one is $499. There are four different Canon 70-200s; they are all expensive; they are all very good.

The other two obvious possibilities where there are pairs of Canon zoom lenses in f/2.8 and f/4 are:

16-35 ultra-wide angle. The f/2.8 lens is heavier, bulkier, vastly more expensive, and doesn't have IS. The f/4 is as good or better at everything except some aspects of low light work (in general, the extra stop makes up for the lack of IS at these very short focal lengths and provides greater compositional flexibility). Personally, I really can't see the point of an f/2.8 ultra-wide, but they are quite popular so obviously not everyone agrees.

24-70 Similar considerations apply. IS becomes more of a factor at these middling focal lengths. On the other hand, the ability to get a fairly shallow depth of field with f/2.8 and (say) 50mm is very useful - much more so than with ultra-wides which have a pretty deep DOF at any aperture. My own view is that the cost and weight saving trumps the shallow DOF, and the IS is a big advantage. With the money saved by not getting a 24-70/2.8 I can afford to buy a nice fast prime (say an 85/1.8) and have the best of both worlds. Note also that if you are thinking about a 24-70/4, you should also consider a 24-105/4. There are reasons for and against both.