Canon 24-70mm not constant 2.8?

[Brandon Ruiz]

It's the lens.

Over the last few months, more than one Canon dealer has discouraged me from buying the 24-70L, saying it doesn't deserve the "L" designation due to softness, distortion, and vignetting - which has been echoed by others. They've all told me to wait for the rumored IS replacement.

[Roberto Lequeux]

Just 0.02, common sense thoughts which you probably already took into account:
_ It seems you lit from overhead, so the higher you measure the higher the values you'll get.
_ Noise will give you slightly different values, so if you want such accurate measurements you'd have to get several measurements and average them out, quite a bit of work.
_ Make sure you measure off the originals or you'll also have to worry about compression artifacts which could give you wildly different readings close to high contrast areas.

[Justin McAleece]

It's an okay lens. I've been using it for a year on the Birger and it definitely ramps on the long end. I would say at least half a stop when at 2.8 and 70mm. It telescopes which sucks the most and overall is a little soft. It's decent but the 16-35 is better for those reasons. It would be pretty awesome if Canon brought out a 16ish-85ish 2.8 that solved some of those problems. I would sell 2 lenses and pay $2K.

[Daniel Browning]

In post I recognized a brightness loss about a half stop
on the longer end of my new 24-70mm Zoom. Is that normal?

No, it is definitely not normal. I traded my 24-70 for a 24mm f/1.4, but I'm certain that the 24-70 I had did not do this. I shot it in manual mode all the time, and I think I would have noticed a half-stop change every time I zoomed.

I think veiling glare is a more likely explanation. Music videos like to have a lot of flaring lights, and at 24mm you'll get more glare/flare from them then at 70mm. The flare is what increases the brightness and gave you the impression of ramping.

If you take an image of an even-toned subject with no sources of glare, I think you'll find that the f-number is indeed constant with zoom.

[Kim Frank]

But Daniel, did you take a look at the quick tests Roberto and me shot?

[Scott Crawley]

It's the lens.

Over the last few months, more than one Canon dealer has discouraged me from buying the 24-70L, saying it doesn't deserve the "L" designation due to softness, distortion, and vignetting - which has been echoed by others. They've all told me to wait for the rumored IS replacement.

For the kinds of still work that I frequently do, it is one of only two lenses that I carry. The other is my favorite, the venerable 70-200L. The 24-70 isn't as sharp, but then I know of no other zoom that is. OK, it has a fall off of brightness at the very end, but we are talking about a half stop. It's still a fast lens, and for still work it is perfectly adequate.

Dan makes a good point. I'll admit that my own test was quick and dirty. I'll give it a more careful go later.

The fact that it does telescope was going to preclude it from getting any Cine use on my future Scarlet, so this fall off news isn't all that upsetting to me. It's good to know though. Thanks for pointing it out.

[Roberto Lequeux]

FYI I didn't have the hood on for those, but there was a lamp shade on that light.

[Daniel Browning]

But Daniel, did you take a look at the quick tests Roberto and me shot?

Yeah, that doesn't look like flare. I must be wrong.

Another possibility is that the f-number is indeed constant, but this is a difference in vignetting. On full frame, there is a conspicuous bright center spot and rapid falloff at 24mm, but since you're using S35, most of the frame is taken up by the bright spot. At 70mm, the bright spot evens out and the falloff is smoother.

[Scott Crawley]

I reshot with a more careful approach and will leave you to your own conclusions. This was for brightness, so critical attention was not paid to focus.

I shot a medium grey paper backdrop and placed 20 targets diagonally across the center. I spot metered just above each target, and entered the average reading on the target for each of the 2 exposures. Camera distance remained unchanged.

I repeated x4:
24mm metered at 1/60 f4.0 8 shot at 1/60 f4.0 ISO 100


70mm 1/60 f4.0


70mm metered at 1/60 f2.8 5, shot at 1/60 f2.8 ISO 100


24mm 1/60 f2.8

[Stephen Williams]

That's a really horrible lens IMHO, OK 70mm F4 but not much good anywhere else.

I reshot with a more careful approach and will leave you to your own conclusions. This was for brightness, so critical attention was not paid to focus.

I shot a medium grey paper backdrop and placed 20 targets diagonally across the center. I spot metered just above each target, and entered the average reading on the target for each of the 2 exposures. Camera distance remained unchanged.

I repeated x4:
24mm metered at 1/60 f4.0 8 shot at 1/60 f4.0 ISO 100


70mm 1/60 f4.0


70mm metered at 1/60 f2.8 5, shot at 1/60 f2.8 ISO 100


24mm 1/60 f2.8