my sigma 24-70 seems dim at f2.8

[goldfries]

All the examples done in AV mode. body is 350D.

ROOM




@this one with flash.


TOYS






OUTDOOR




this one at 24mm


------------

what do you guys think?

in the ROOM test, the f2.8 seems washed out. contrast is appalling.

in the TOY test. f2.8 has dimmer background. same goes to the OUTDOOR test. contrast seems to be closer.

[Adrian Wong]

What ISO did you use and what were the shutter speeds?

[Falcone]

You cannot compare it using matrix metering and aperture priority, it's letting the camera decide the exposure for you which is probably the cause of it, but since we are testing your lens.

Set it at manual one at

Exposure 1/250
Aperture: f/2.8
ISO equiv: 1600

the other
Exposure 1/125
Aperture: f/4.0
ISO equiv: 1600

and fix the WB also

[goldfries]

yes. WB is fixed all the while. I'll try out your suggestion (which is by far the best I've come by)

anyway I've tested AV mode with my 50mm f1.8 and here's how it looks.


looks fine. anyway I just tested the stuff using manual mode, still dimmer on f2.8.

however earlier (after posting this thread) I've done other tests and seems like exposure was fine on the 24mm side.

[goldfries]

Originally Posted by Adrian Wong

What ISO did you use and what were the shutter speeds?

sorry Adrian, missed your response.

which example? anyway they were all using constant ISO and WB.

since it's AV mode, only aperture and the corresponding aperture.

anyway latest tests shows that the exposure between f2.8 and f4.0 are same on other zoom range like 52mm and 24mm.

it's just at 70mm it shows the brightness difference.

[Falcone]

Hmmmn guess maybe is the long extension might have reduce the light comming.

Got anyway of getting second copy of the lens?

[goldfries]

no idea how to get 2nd copy of the lens, unless i bring to Sigma disti.

tried manual mode, also outcome same.

i was expecting the exposure for f2.8@70mm to be same as f4.0@70mm.

as of now
exposure between
f2.8 and f4.0@52mm are same
f2.8 and f4.0@24mm are same

want to say body problem also cannot. want to say lens problem, also cannot.

the thing is this lens extends as it goes wide (24mm). so yeah, you turn the zoom barrel to go wide. weird lens, but definitely nice at f4.0.

since it still has 10 months warranty, I'm not making a fuss out of it yet. after all, f4.0 is nice.

[Adrian Wong]

Hmm.. The way I see it, Falcone's method should work best to see if f/2.8 has a problem. Both pictures should have the same exposure.

[Ishtim]

I too would force it in manual mode. Rather odd that 2.8 looks darker than 4 if all else is held constant. Can you try another body too?

[goldfries]

Originally Posted by Adrian Wong

Hmm.. The way I see it, Falcone's method should work best to see if f/2.8 has a problem. Both pictures should have the same exposure.

i tested with manual mode already. still turns out like that.

only dims at @70mm

Originally Posted by Ishtim

I too would force it in manual mode. Rather odd that 2.8 looks darker than 4 if all else is held constant. Can you try another body too?

i would've done that if i have. i should be able to do that within the week or 2.

---------

Now, I've tested Falcone's suggestion

Exposure 1/250
Aperture: f/2.8
ISO equiv: 1600

Exposure 1/125
Aperture: f/4.0
ISO equiv: 1600

Now I've tested the above settings @70mm, seems that the Exposure level indicator shows that the f2.8 settings is 1 level lower than at f4.0.

it's like if the f4.0 was at -1/3, then the f2.8 was like -2/3 (yes, tested it again. it sorta moves. staying around -2/3 most of the time. yes. target same spot)

I tested the above again, this time @24mm, this time the exposure level indicator is the same for both f2.8 and f4.0



what do you guys think? faulty lens?