24-105 f4 loses more light than expected
 

I just got a Canon f4 AF IS L zoom and am finding to my chagrin that f4 on this lens is nearly a stop darker than on any of my other lenses. Thus I'm sacrificing 2 stops instead of the expected one for the additional reach.
Can any one else verify this or is something wrong with my lens?

Lenny Levy

I have this lens as well, though I have never tested the difference. My only other lenses are primes but will run a test and see if it applies! For sure the 24-105 is not the go to lens for indoor shots though. I have only used it outdoors or in very well light venues.

Zooms will nearly always gather less light than a prime at the same aperture; there are more elements in a zoom, thus more chance for light to go astray. Lucky the 7D has high ISO!

Remember depth of field will remain the same, at the same aperture and focal length between prime and zoom, despite the loss in sensitivity.

You're not alone here. It is a slower lens then I would have hoped as well. However it's still my favorite lens to use for most situations.

Liam ,
I do understand the issue. It is why Cine lens are calibrated in both T stops ((Transmission Stops) and F stops. I am just surprised at how much loss there is, and it affects whether I want to keep the lens. i think I could have lived with 1 stop less than the 2.8 zooms, but 2 stops?

None of my other still zoom lenses do this. I think my Nikon 80-200 f2.8 measures the same as my primes.
My Tokina f2.6-2.8 28-70 is much faster than the Canon at f4 for example.

I bought this lens to shoot video interviews under lights and have not had any problems. Indoors I have to rate it at 320 or 640. The 7D has such good low light performance that this is not a problem.
Recently I shot in a relatively dark room @ 2000 iso and it did not look that bad. Another 7D with a 50 1.4 Nikkor shot at 320. That is 3 stops different.
I have not noticed a two stop difference from a 2.8.

Alan

Yes, I'd say that there is indeed something wrong with your lens. Although there are differences in light transmission between zooms and primes marked with the same aperture (T and f stops) the differences are minute in this day and age of super multi-coating.

Have a look down into your lens as you change aperture, make sure the blades open fully at whatever focal length you've set it at. Don't forget what you're saying - a stop darker suggests the lens isn't opening beyond f/5.6. A stop slower means you've got to double the light in the room for the same exposure.

tom.

I have the EF 24-105mm f4 L IS USM lens also. I had the same reaction when using it for the first time. Thought I might have put a filter lens on the front instead of the protective one. When deciding to get this lens, none of the reviews mentioned how dark it was. For me, it was a toss-up between this and the EF 24-70mm f2.8L USM. I like IS and thought I'd get lots of use out of the extra reach. Now wish I'd gone with the 24-70mm because even outside I find its use is too limited. I don't think there's any defect with your lens.

Went to Calumet today and compared it to a 17-55 and a prime 85. Confirms my tests at home. Its not ramping, not losing light on the long end its just flat out about a stop slower than every other lens I've tried at f4. I'd call it a T5 or T5.6. 17-55 by the way matched the prime.
I'll have to test my buddy's 70-200 f4 and see if it has the same problem.
Funny that none of the salesmen at Calumet knew it.

Lenny levy

Which is why cine lenses are calculated to T-stops.

Sorry Leonard, I wasn't trying to teach you to suck eggs, but thought it would be useful for some of the newbies to understand. Also, I agree, 2 stops is crazy!

But
 

The IS more than worth it IMHO. It removes so much vibration and mishandling! I've used both the 24-105 and 24-70, and for general, everyday shoots the 24-105 takes the cake for me. If I need low light, I'll put on my 50mm.

F4 on 24-105 is darker
 

Both of my 24-105's let in less light at F4 than my 24-70L does at F4 on my 7D. On my 5DII, the difference is more like 2/3 stop less light (all lenses at F4). The 24-105 vignettes more on FF than the 24-70, so the lens is even darker in comparison to the 24-70 on the 5D.

I've been using these lenses for years on the still photography side, and the 24-105 is known to be a "dark" lens.

These still lenses are identified by F stops, not T stops, so from lens model to lens model, you can get a variance in actual light transmission through the block, and is influenced by factors such as vignetting, number of elements, optical formula, coatings, internal flare, grade of glass used, whether there are aspherical elements used, and if so, whether it contains molded resin vs ground glass elements, etc....

It'd be cool if someone could test all these lenses and rate them for light transmission, so one could determine that when selecting a lens.