Overposure at high ISO (1 Viewer)

bobmoose

Bob Moore

• Sep 23, 2014

• #1

I am using a Canon 300mm IS 2.8/1.4x combination with my 7D. It works fine with low ISO but have noticed recently , as the light is getting duller and I need higher ISO that when I shoot at 1600 my images need to be underexposed by up to two full stops to not be completely blown out . I meter to a neutral exposure setting normally . I don't know what the problem is. It doesn't seem to be a problem with my 400mm 5.6. Any ideas?
Thanks

 

M

Malcolm Stewart

Well-known member

• Sep 28, 2014

• #2

Morning Bob,
I've just run a check with my 7D (bought new last January, Firmware 2.0.5), 1.4x Canon Mk I extender & EF 300 F/2.8L IS. The shots were taken outside, tripod mounted, in cloudy bright conditions, and with Exposure Compensation set to 0. I used ISOs of 200 and 1600.
With my 7D, there's very little variation in density across the set, and the histograms are near identical, just touching the right hand edge.

The last one is without the extender.

Sorry about the poor subject, but I wanted something which would be stable in brightness for a few minutes.

 

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Telephoto Paul

Well-known member

• Sep 29, 2014

• #3

These sorts of problems can often be causes by mechanical issues with either the shutter or lens diaphragm. (eg. the camera requests f4 but the lens is stuck at f2.8 so the photo is over-exposed by a stop) That your 400mm is fine points towards the diaphragm of your 300mm is playing up. However, that it only occurs in low-light, high ISO is confusing, as I assume you're trying to shoot as the same aperture all the time.

Does the same behaviour occur with and without the extender?

 

Last edited: Sep 29, 2014

O

OPTIC_NUT

Well-known member

• Sep 29, 2014

• #4

Malcolm, I'm seeing noise that's the worst at 1/30s - ISO 200
Something is odd there, like a chip/firmware no average out noise
or a micro-fluctuating light source (blowing fog, etc).

 

Last edited: Sep 29, 2014

M

Malcolm Stewart

Well-known member

• Sep 29, 2014

• #5

OPTIC_NUT said:

Malcolm, I'm seeing noise that's the worst at 1/30s - ISO 200
Something is odd there, like a chip/firmware no average out noise
or a micro-fluctuating light source (blowing fog, etc).

Click to expand...

Hi, are you referring to my posted examples? If so, it's probably the application I used to reduce the image size and add the annotation.

Or, are you trying to give me "owners disease" with respect to my 7D?! If so, I'll go back to my 1D IV.

 

bobmoose

Bob Moore

• Sep 29, 2014

• #6

Hi,
It doesn't happen all the time. It's intermittent . Like one of those noises your car makes , except when the mechanic wants to hear it. LOL . Maybe time to take the lens and camera to the shop.

 

bobmoose

Bob Moore

• Oct 4, 2014

• #7

Hello all again,
The problem may have been the setting on the Auto Lighting Optimizer on the camera. I'll try for a while with this setting disabled and report back.