70-200 f2.8 to f4 low light focus difference

for those of you that have\had both the f2.8 and f4, does the 2.8 focus appreciably better in low light? I'm thinking of moving to the 2.8 IS II from the 4 IS.

Thanks

The both focus fast in low light.

Marloon wrote in post #11634241
The both focus fast in low light.

I'm talking very limited light. Can the 2.8 attain focus at a lower light level?

why post this in here instead of the lens forum?

i have owned both. both can attain focus fine in any light where you will be able to get an acceptable exposure. does that make sense?

once the light gets too low you wont be able to get a proper exposure anyway.

CosmoKid wrote in post #11634297
why post this in here instead of the lens forum?

i have owned both. both can attain focus fine in any light where you will be able to get an acceptable exposure. does that make sense?

once the light gets too low you wont be able to get a proper exposure anyway.

Oops, force of habit.

We'll see if a mod will move

Sorry

CosmoKid wrote in post #11634297
why post this in here instead of the lens forum?

i have owned both. both can attain focus fine in any light where you will be able to get an acceptable exposure. does that make sense?

1 stop difference I would think would give the 2.8 an edge.

Correct. Faster glass passes more light, and in low light situations, the AF sensors get more light to help lock on.
From a practical standpoint, what the other poster said is pretty much true though: they both do an excellent job of locking onto focus in most any situation where you'd really want to take a picture. At least on a 1DMk2, which is all I have recent experience with.
If I were shooting with the f/4 version still ( I'm not, because I sold it after buying the 2.8 ) I'm not so sure I would spend the extra money up to the 2.8 if all I were searching for was better AF in low light.
Make sense ?

I haven't had f4 for last 4-5 yrs so don't know side my side but this weekend using 70-200mm f2.8 IS II in low light I had heck of a time to AF when using my 5d. I had to simply pack and go home. It was bad bad. Not sure if it was my 5d or the lens. And all I was trying to shoot was a model, nothing moving.

Depening on what you shooting, AF assist of some sort will be better option.

What body are you using?

I'm no technician but the 7D says it has 19 cross type AF points and that focus is more sensitive for f2.8 lenses. AF working range: -0.5 - 18 EV

I was shooting a stationary subject in my living room over the weekend with a 7D. Radio popper studio in the hot shoe so I couldn't use an on camera AF assist source.

I've looking at the 2.8 II over my F4 IS for a few reasons:
1 - using a TC and still having auto focus
2 - 1 more stop
3 - possible increase in low light AF ability (now this doesn't sound like an advantage)

Thanks for all the responses.

Ralph

Hmmmm. From all I've heard, I'm not too surprised to hear Bobby say that the 5D struggled, but the 7D being more modern, I would have thought it would do very well.
Not to put too fine a point on it, but if low light AF is important to your shooting, I have a couple words for you : one series.
On the 1D Mk2, at least when using the center AF point, I very rarely have a problem getting it to AF. Occasionally in a dimly lit horse arena, when the AF point is laying on an area of little to no contrast, like the solid color part of a horse in the distance, it may fail, but a quick reposition to an area of contrast solves the problem.
When I first got my one series, the AF was far superior to the 20D and 50D that I had, it made me want to sell them. So I did.

I've not used a 70-200/4.0 on my 7D but I do use the 2.8 IS version with a 2X extender to shoot soccer. Last Saturday's game was so overcast that I was shooting ISO 4000+ and having no issues with focus speed.

But my point was - the body will probably be more important and the 7D should be one of the better ones.

How about shooting with a 40D?

I've had both and I usually shoot in pretty dim light (with a 7D). They both worked very well and I didn't notice that one was better than the other. I never pushed it to the limits in a dark area where I wouldn't get a usable exposure. Not sure if that was any help.

windpig wrote in post #11634106
for those of you that have\had both the f2.8 and f4, does the 2.8 focus appreciably better in low light? I'm thinking of moving to the 2.8 IS II from the 4 IS.

Thanks

I have both, and there's a slight edge to the 2.8 in low light for autofocus. Slight, at best. The advantage of the 2.8 is will accept both 1.4X and 2X TC's and retain autofocus on my 50D. The f/4 version will only autofocus with the 1.4X.