The Light Leak Issue

[altenae]

Hmmm only affects  my 5D3 without a lens and thumb instead of cover too. No issue with lens on or rubber cover on eyepiece .... LOL"

It sounds like this effect is only observed when there is so little light that the sensor is blindly guessing at the exposure. What is the "correct" exposure that the camera should be reporting when the camera has the lens cap on and viewfinder closed?

So it just could be the exposure readings with cap on and VF covered are NOT correct at all.
So how do we know what the impact is when the LCD light is on ?

Anyway NO issue without the lenscap at all

[Mt Spokane Photography]

The metering sensor is under the mirror and is used to set aperture and shutter speed.  This means light is getting to the metering sensor.  Obviously, if it gets to the metering sensor, then it probably gets to the main sensor as well, its just not very much light.

The metering sensor was under the mirror in old designs, but these days it's actually up in the pentaprism housing (labeled in the upper right of this diagram taken from a Canon tech report):



So, light that reaches the metering sensor should be blocked from hitting the image sensor by the mirror when it's flipped up during the exposure.

 
+1
 
OOPS, its the AF sensor down there.  I knew that, just getting too old.

[zim]

The metering sensor is under the mirror and is used to set aperture and shutter speed.  This means light is getting to the metering sensor.  Obviously, if it gets to the metering sensor, then it probably gets to the main sensor as well, its just not very much light.

The metering sensor was under the mirror in old designs, but these days it's actually up in the pentaprism housing (labeled in the upper right of this diagram taken from a Canon tech report):



So, light that reaches the metering sensor should be blocked from hitting the image sensor by the mirror when it's flipped up during the exposure.

 
+1
 
OOPS, its the AF sensor down there.  I knew that, just getting too old.

Had a couple of noggins tonight guys so maybe not thinking to straight but what then does that piece of rubber crap that goes over the eye piece do for things thats attached to the camera strap?

[DavidRiesenberg]

It is meant to prevent light from entering through the viewfinder when you're shooting on a tripod. And using it is a must if you don't have time or want to tweak the exposure manually.

[zim]

So why did they remove this especially from 'pro' cameras?

[Stephen Melvin]

So why did they remove this especially from 'pro' cameras?

You see that little lever? It activates the internal shutter blind, so we don't need to carry around that little rubber piece of junk.

On the other hand, that eyepiece blind is a frequent point of failure in Nikons.

[HughHowey]

So why did they remove this especially from 'pro' cameras?

You see that little lever? It activates the internal shutter blind, so we don't need to carry around that little rubber piece of junk.

On the other hand, that eyepiece blind is a frequent point of failure in Nikons.

Really? I've always wondered why Canon didn't include that feature. Always thought it was nifty.

[AUGS]

The metering sensor is under the mirror and is used to set aperture and shutter speed.  This means light is getting to the metering sensor.  Obviously, if it gets to the metering sensor, then it probably gets to the main sensor as well, its just not very much light.

The metering sensor was under the mirror in old designs, but these days it's actually up in the pentaprism housing (labeled in the upper right of this diagram taken from a Canon tech report):



So, light that reaches the metering sensor should be blocked from hitting the image sensor by the mirror when it's flipped up during the exposure.

100% confirmed - for my 5D3.  I have done these crazy tests and most importantly - every frame I exposed (using manual focus) came out completely black.  Therefore, no stray light from the “metering leakage” is getting to the sensor.  I even did a 120 second bulb exposure with direct sunlight onto the LCD panel at ISO800 and only the slightest stray light was witnessed and that was found to come through the VF cover – so it isn’t perfect either.  When I removed this tiny VF leak, a 256 second bulb exposure got absolutely nothing. To put in context, a proper exposure was 1/1000 second at f/8.

[spinworkxroy]

Oh no..
i think we have a bigger design flaw here than just the 5D3 light leak..
After all the tests done, i think the biggest flaw is….OUR thumbs leak light!!!
So all those years of covering someone's eyes with our hands proved to be useless!! They can still see with light leaking through!!! Oh no…wonder if we will be recalled.

[dilbert]

The image sensor has nothing to do with the metering settings on the display.  The metering sensor is under the mirror and is used to set aperture and shutter speed.  This means light is getting to the metering sensor.  Obviously, if it gets to the metering sensor, then it probably gets to the main sensor as well, its just not very much light.

Depends - the mirror swinging up might block off the leak.

[D.Sim]

So why did they remove this especially from 'pro' cameras?

You see that little lever? It activates the internal shutter blind, so we don't need to carry around that little rubber piece of junk.

On the other hand, that eyepiece blind is a frequent point of failure in Nikons.

Really? I've always wondered why Canon didn't include that feature. Always thought it was nifty.

I await the day that Canon releases an eyepiece extender with a little lever for us to close a shutter within the extender for the same effect....

[skitron]

Oh no..
i think we have a bigger design flaw here than just the 5D3 light leak..
After all the tests done, i think the biggest flaw is….OUR thumbs leak light!!!

Dang good thing they do! Otherwise those thingies they put on your thumb or finger at the hospital to check your O2 level wouldn't work so hot. 

Moral to the story: thumb - good for O2 testing, not so much for keeping light out of the viewfinder! 

[highnfar]

have you done tests like this in the video below?

http://youtu.be/oF8CW723wEo
	Small | Large

[nickzh]

I just did a similar test, taking two outdoor pictures with my new 5D MK iii. The one without the lcd light on is metered for 10" exposure duration and turns out fine. When I use the lcd backlight the meter shows 6" exposure duration and the shot gets underexposed by almost one 1 stop.
I acknowledge these tripod mounted night shots with long exposure duration are not the ones I do regularly, but to me the light leak problem seems very real.
So, should I send the camera back?

[Kernuak]

I just did a similar test, taking two outdoor pictures with my new 5D MK iii. The one without the lcd light on is metered for 10" exposure duration and turns out fine. When I use the lcd backlight the meter shows 6" exposure duration and the shot gets underexposed by almost one 1 stop.
I acknowledge these tripod mounted night shots with long exposure duration are not the ones I do regularly, but to me the light leak problem seems very real.
So, should I send the camera back?

Is it normal practice (for you or anyone else for that matter) to have the LCD backlight on when metering? If your answer is no, then just use it as you normally would and don't waste your time and potentially money returning it. If yes, then may be you need to review your practices and/or make manual adjustments.