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The value of F/2.8

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joehewes

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A typical post on this board queries about the relative merits of the 24-70 f/2.8 vs. the 24-104 f/4 IS. Opinions vary, there are many who LOVE either lens. But I find myself asking the question, isn’t f/2.8 valuable beyond shallower depth of field? On the 20D and other cameras one takes advantage of the cross-type center focus point only at f/2.8 and wider. Is the advantage of faster, more accurate focus that much mitigated by IS? Is the activation of the cross-type sensor not that big a deal or big advantage? When I look at lenses I look at max aperture first, thinking I want the brightest image in my viewfinder, and the ability to take advantage of that more accurate focus sensor. Any comments on this?
--
Joe
 
For me the real plus of faster lenses is the ability to use them without flash in lower light. Most of the time I don't look for very shallow DoF with the type of photography I do but that is also a plus for some. Better autofocus performance is also a big benefit although in practice I can't say I see a major difference, at least not in good light.
 
I think you've identified several important characteristics about these two lenses. Size / weight is another concern for many. I've had 24-70L for a couple of years, and had a 28-70L before that. The 24-70 looks to be a nice lens, but I doubt I would be willing to part with f/2.8 myself. But for many people, that seems to be just what they're looking for.

One rationalization I've heard to support that f/4 is good enough is that lower noise at higher ISO will make up for the extra stop between f/4 and f/2.8. Of course you still can bump up the ISO on an f/2.8 lens, so this never has made sense to me.

Of course in reality, I'm not sure f/2.8 actually saves me from using flash that much anyway. It seems like to get away from flash indoors I have to go with a fast prime.

This is just based on the conditions and subject I shoot though, to each their own.

Best of luck,
Barry
joehewes said:
A typical post on this board queries about the relative merits of
the 24-70 f/2.8 vs. the 24-104 f/4 IS. Opinions vary, there are
many who LOVE either lens. But I find myself asking the question,
isn’t f/2.8 valuable beyond shallower depth of field? On the 20D
and other cameras one takes advantage of the cross-type center
focus point only at f/2.8 and wider. Is the advantage of faster,
more accurate focus that much mitigated by IS? Is the activation of
the cross-type sensor not that big a deal or big advantage? When I
look at lenses I look at max aperture first, thinking I want the
brightest image in my viewfinder, and the ability to take advantage
of that more accurate focus sensor. Any comments on this?
--
Joe
Click to expand...
 
You are right: large apertures have many advantages other than brighter viewfinder.

First, there is certain non-binding law that 2.8 aperture in zooms means the very highest overall quality. Companies could, in theory, build poor 2.8 zooms and excellent 3.5 zooms, but they don't.

24-105/4 and 70-200/4 are rare L-level exceptions, but even they AFAIK don't have the same feature as the 2.8 versions: almost full IQ at the largest aperture. 70-200/2.8 is practically perfect at 2.8, but most other zooms have the first high quality f-stop at about 5.6 or so.

Second, not every f-stop is created equal. You could say that 2.8 and 1/60 is the same as f/4 and 1/30. In theory, yes, but in practice, no.

There is an old joke from the film era that f/11 and 1/125 is ALWAYS the right exposure. The meaning of the joke is that when shooting in sunlight with 100 ISO film, this really comes close to being true.

In similar manner, many situations in real life photography dictate certain steps or barriers that your tools must achieve. 2.8 aperture is one of those. Very often you really, really need the f-stop to be 2.8 and you cannot substitute it with f/4 and longer time.

This comes from a complicated combination of the typical interior light, typical DOF needs and typical shutter time needs. 2.8 is actually on the very edge of usability, so f/4 will not cut it at all.

This is why professionals seldom use zooms anyway when shooting indoors. They pay top dollar to get stuff like 85/1.2, so they can achieve the often necessary combination of totally-sharp-but-selective-DOF f/2, facial-movement-stopping 1/60 and technically-good-enough 800 ISO. There is no way that you could do the job with theoretically "similar" f/5.6, 1/30 and 1600 ISO.

2.8 zoom is also crucial in indoor sports. It just happens to be so that most arenas have "always-right" exposure of 2.8, 500, 1600 ISO. You cannot use f/4 and 250, because 250 doesn't stop a moving human being. 3200 ISO is (or has been) out of bounds for high quality pics, and f/4 also gives you so deep DOF that the background becomes too sharp and distracting.

Regards,

Ravalls
 
Size and weight are huge for me. For a travelling, walking around, day lens this makes a huge difference to me. I would rather switch to one of my fast primes on the occassion I need speed in low light and carry the 24-105L most of the time.
--

All Canon: 20D, 24-105 4L IS, 200 2.8 II, 85 1.8, 50 1.4, 35 1.4L, 420EX Speedlite, 580EX Speedlite, Kenko 1.4 Extender
 
All I know is the 24-105 will AF in as low a light as I've ever needed to shoot in on the 5D. Maybe all the credit should go to the 5D though.
 
It has the speed of the 24-70 plus the smaller size, weight, and IS of the 24-105. For most people it's also a better FL range on a crop sensor. In other words, this lens was tailor-made for APS-C sensors, while the other two were made for FF cameras.
 
for me anyway. the 24-105L puts me right in sweet spot with excellent IQ, IS and plenty of speed. even with f2.8 lenses i generally stop down to at least 3.5 or 4 for sharpness and 2.8 is practically worthless indoors.

i should add that while i find 55mm too short it's long enough for great portraits and i have no doubt that this will be a very popular lense, especially initially.

btw, these forums are lousy with indoors sports and wedding shooters :).

ed rader

--



'One often has mixed feelings about relatives, but few people could identify serious problems in their relationships with dogs.'

-- Anonymous
 
I really can't tell a difference in autofocus speed or accuracy with either lens on either of my cameras (5D, 20D). Strangely, I don't notice much difference in viewfinder brightness either.

For me, the 24-105 is the better lens (versus the 24-70L) because it's longer and has IS. When I need speed for real, f2.8 is usually not nearly enough. So I also have the 35/1.4L and 100/2. I'd love to have an 85/1.4L IS if they made one.

If you are willing to use fast primes when serious speed is necessary, the 24-105IS a great lens (it is sharp wide open, corner to corner). If you aren't willing to use primes, the 24-70 does provide a little extra speed.

--
Lee Jay
(see profile for equipment)
 
Bruce MacNeil said:
f2.8 as a maximum aperture is a fairly recent phenomenae. That
recent adopters of photography think f2.8 is a pretty wide and fast
lens. Simply not true.
Click to expand...
For many if not a majority of all applications f/2.8 is eminently useful. You probably have a specific subset of all applications in mind when you say f/2.8 can't be used for "most applications".
 
It AF in low light pretty good on my 20D also. All the nonsense talk of f2.8 and cross sensor. You have to compare lens by lens. There are so many other factors determines lens AF speed and accuracy. Enabling the cross sensor is just one of them and probably not even among the most important ones.
Rich Dykmans said:
All I know is the 24-105 will AF in as low a light as I've ever
needed to shoot in on the 5D. Maybe all the credit should go to
the 5D though.
Click to expand...
 
thanx lee jay. both of those arguments have always seemed pretty lame to me. i've never really looked for it but i can't say that i have ever noticed any difference in viewfinder brightness with any lens.

i'm middle age but i see well enough to compose a shot and then let AF take over.

i don't own a 20d yet (tho i'm ready to pull the trigger) but you don't hear much about the improved focussing of f2.8 lenses until you read threads like these.

i think the real world differences of these two are negligible.

ed rader

--



'One often has mixed feelings about relatives, but few people could identify serious problems in their relationships with dogs.'

-- Anonymous
 
I have both the 24-70 and the 24-105 and there is a distinct difference in AF speed between the two lenses using the center AF point in lower light. The 24-70 is definitely quicker. Having said that, in such circumstances I am still more likely be able to get the picture with the 24-105 than with the 24-70 (assuming little subject motion) due to the 24-105's IS. As one of the other posters above mentioned, practically I don't use either of these lenses much in doors, though. It is the 35 1.4, the 85 1.2, or the 135 2.0.
 
paul -- do you think the diffrence is speed is necessarily because of aperature or possibly another factor like lens length?

thanx,

ed rader

--



'One often has mixed feelings about relatives, but few people could identify serious problems in their relationships with dogs.'

-- Anonymous
 
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