Canon EFS 18-55 underexposing at large appertures

chemosabe

chemosabe

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Hi all :cuckoo:,

This is my first post on the forum. Have been refering to the forum a lot over the last few months and recently bought a canon 40d, EFS18-55mm f3.5 IS II and 70-300 f4 IS USM.

I've noticed that when using the 18-55 lens with no exposure compensation, at large apertures from f3.5 - f5 the image tends to be underexposed by about 2/3 stop. From f5.6 and upwards, all the images have the same exposure and appear correctly exposed.

This happens in Av mode, or in Manual mode when adjusting the speed and aperature for a neutral exposure. Haven't checked in P or Tv mode as I haven't used them yet.

I'm not talking about the vignetting around the edges, there's hardly any that I can see, it's the entire image that is darker.

I can correct this with the exposure compensation.

My question is: Is this a feature of the lens, camera, or is it me? Is it a case of accepting this and overexposing when shooting at larger apertures?

Chris
 
Have you done some test shots to prove this? Same scene on a tripod, Av mode and just change the aperture between shots.

You shouldn't be seeing a difference.

Oh and welcome to the forums :)
 
I did test shots of the same scene with all the aperture settings in Av mode from f3.5 - f22. The camera was on a solid surface, don't have a tripod at the moment.
Did this on 3 different scenes in my garden. The shots at F3.5 - 5 were darker by 2/3 stop. The smaller apertures from f5.6 and up all seemed to have the same levels of exposure.

I'll take some more test shots tomorrow.
 
it could be because that lens is sharpest around f/8, this lens isnt very sharp and the colours arn't that saturated when using the maximum aperture.

this isnt a factual reply, im just speaking from personal experience.
 
Just check that the aperture blades aren't sticking partially closed.... not uncommon.
 
chris_tim,

I think you may be right. Just seen some analysis of the lens on http://www.photozone.de/Reviews/Can...18-55mm-f35-56-is-test-report--review?start=1.

After doing some more tests today, I think it may indeed be the vignetting, as the problem irons out at around f5.6. And the amount over exposure compensation I was having to apply ties in pretty well with the values on the vignetting analysis.

Surprisingly the test did say that the image sharpness was exceptional for this range of lens...

I guess if I want to use the larger apertures just need to remember to over expose using a scale as per the link above.

Thanks CT, the blades seems ok. It's down to the newbie geting to used to all the variables.
 
The lens is wide open when the camera meters the scene so I don't understand why it should under expose at wide apertures. Vignetting means dark corners, it shouldn't affect the exposure of the bulk of the picture.

Can you try the lens on another camera or borrow a similar range lens to try on yours?
 
Good suggestion, I'll check it with a mate of mine who has an older 5d. He's also got some L optics (I think), so would be interesting to see. As the darkness isn't limited to the edges perhaps it's something else?

I'll report back when I've got round to doing some tests, but might not be until next weekend.

Cheers,

Chris
 
Your EF-S lens won't fit on a 5D - but lenses from the 5D user will fit your camera fine.
 
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