Which of "these two" is sharper

[pepperoni]

Holy smokes, this forum moves fast. Here's my question.. which of these two lenses are sharper at F/4?

Canon 70-200 f/4L shot at f/4 (at both ends of the focal range)
or..
Canon 70-200 f/2.8L shot at f/4 (at both ends of the focal range)

PS. My primary interest is amatuer motorsports photography, and if you haven't already guessed, I'm trying to decide if I really "need" the f/2.8.

Thanks.

[schmoelzel]

Well, a lens that is stopped down is generally sharper than a lens wide open! From my limited experience (I have owned and used both lenses), the f2.8 is sharper at F4 than the F4 lens at the same aperture. Some lenses, 135F2 and 85L are as sharp wide open (or very close) as they they are stopped down........I find that my 85L is very sharp at F1.2 and obscenely and sometimes too sharp stopped down to f2.8! Most lenses seem to reach their optimum sharpness at the f5.6 mark............

[pepperoni]

Thanks. I'm assuming (maybe inaccurately?) that I'll want stop-action shutter speeds, so if I get the f/4 version I can see myself shooting it wide open to achieve that. I don't want to break the bank, but I do want a tool that will work.

John

[illy]

Firstly, if there is a difference between the two it will be minute. Secondly, the quality will still be more than enough. Thirdly, f/2.8 @ 200 @ f4 has an MTF value of 1937, 1877; f/4 @ 200 @ f4 has an MTF value of 1820, 1747. Both of these are above 1800 (excellent) so you shouldn't worry.

[Tee Why]

I wouldn't let the sharpness at f4 be the deciding factor as with processing, the differences in sharpness will be trivial to all but the most intense pixel peepers.

If you are interested in sports, I'd recommend the f2.8 which will double the shutter speed over a f4 aperature with same lighting. If the Canon f2.8 version is too expensive, consider some alternatives from Sigma like the 70-200 f2.8.

[pepperoni]

Thanks. Ultimately, I think the 2.8 is the right choice. It's just more expensive and at my rookie level, I'm not sure if I can justify the cost to myself.

[Woolburr]

The f/4 version is more than ample for motorsports...most times you want shutter speeds of 1/320 or less to show some motion blur in the tires and wheels...so the cars don't look parked. Not a problem with either lens.

[Ronald S. Jr.]

I'm very against limiting myself and my options, as long as budget permits. I like to always have f/2.8 or faster, that way if I need it, it's there. You can always stop down a 2.8 lens to 4, but never the other way around. If you can afford the 2.8, I'd absolutely get it. If not, f/4 may work.

[DaveG]

Holy smokes, this forum moves fast. Here's my question.. which of these two lenses are sharper at F/4?

Canon 70-200 f/4L shot at f/4 (at both ends of the focal range)
or..
Canon 70-200 f/2.8L shot at f/4 (at both ends of the focal range)

PS. My primary interest is amatuer motorsports photography, and if you haven't already guessed, I'm trying to decide if I really "need" the f/2.8.

Thanks.

There's an interesting factor that you may have not considered here. Let's say that the f4 is sharper than the f2.8 at f4. It won't be much sharper, and I say this because I own the 2.8 and I know how sharp it is at f2.8, never mind f4. But let's just say it is sharper.

Now in real life you are going to shoot and you have a choice. Let's also say the light level at ISO 400 is 1/500 @ f2.8, which of course is the same as 1/250 @ f4. With the f2.8 lens you could choose either exposure, while with the f4 you'd have to use the 1/250 one, or you change the ISO. It's my opinion that 1/500 will give you a better, sharper, image; overwhelming any marginal deficiencies that the faster lens might suffer from. 1/250 is just not as good and you can't change it without using a higher noise ISO.

This is also the same argument I use against the new 70-200 f4 IS. IS is great and if you didn't like it you could always turn it off. But IS has nothing to do with stopping subject blur. Only a fast shutterspeed will do that. I can only assume that Canon has discontinued the 70-200 f2.8 L (non IS) since it's priced at what the new 70-200 f4 IS is going for. In fact the f4 is more than the 2.8 if you buy the trpod collar which is included in the price of the 2.8. The f4 IS is $1050 + $120 ($1170) from B&H, while the f2.8 is $1100!

Except that the f4IS is much lighter than the f2.8 - and that can be an issue for some people - I see no other reason to buy the f4, at least at this price. I can always use a poor man's IS (a monopod) to steady a camera, but once again it does nothing to stop movement of the subject. f2.8 does.

Intrinsic lens sharpness is only part of what makes an image sharp, and I think that you have to keep this in mind.

[sirsloop]

yeah this is one of those questions that really cant be answered. Both of these lenses perform REALLY REALLY WELL wide open. You'll be happy shooting between f/2.8 and f/4 on either lens.

[CyberDyneSystems]

Both are super sharp wide open,

But the f/2.8 stopped down the f/4 is sharper than the f/4 wide open.

In all cases the differences will not anything to worry about, and may not even be perceptible.

[Big Hands]

They're both sharp wide open, blah, blah, blah. The IQ of either of these are so close that it should never be a deciding factor as to which one you should get.

I have used both for shooting motorsports and 'hands down' the f/2.8L version was far better. The AF works better with lenses that have apertures of f/2.8 and larger. The keeper rate was immediately noticeable and I could even shoot with the f/2.8L at night and get very good output:

70-200 f/2.8L at 70mm, ISO 800, 1/250th @ f/2.8

http://photos.imageevent.com/johansen01/letsgoracin/sonyhd5002005/Pit%20Chaos%202a.jpg

70-200 f/2.8L at 70mm, ISO 800, 1/250th @ f/2.8

http://photos.imageevent.com/johansen01/letsgoracin/sonyhd5002005/Bestwick%201a.jpg

70-200 f/2.8L at 200mm, ISO 1600, 1/1000th @ f/2.8

http://photos.imageevent.com/johansen01/letsgoracin/nascar2005/Reckless%20Robbie%201a.jpg