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DPChallenge Forums >> Hardware and Software >> Canon 6D Metering in Dim Light
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10/10/2014 11:12:16 PM · #1
Hi. I just got the Canon 6D. Love it. Still fooling around with it and the options since its a pretty decent upgrade from my Canon 20D (also love it).

One thing I noticed is the metering seems a bit off in very dim light.

Given a room that is relatively dark except for some ambient light from the next room. I set both cameras to f4.0 (Tamron 28-75 on the 20D and the Canon 24-105 'kit' lens on the 6D).
Set both cameras to ISO 1600 and metering mode the same (center weighed in this test, although the method didn't matter).
Manual mode.
Picked a dark spot in the room and adjusted the metered exposure to +2.

The 20D metered a shutter of 25 seconds.
The 6D metered a shutter of 4 seconds. Setting 25 seconds provided the correct exposure but was way off the scale.

All other meterings in normal light seem fine, though I haven't done a comparison (will do shortly).

What's up?

Thanks,
Paul

ETA: Just checked something with a bit more light. Same ISO. Metered on same spot. Exposure to +1
20D: 1/5s
6D: 1/13s - 1/15s

ETA: Swapped lenses and picked a different subject. Both cameras metered exactly the same.
Checked with the lens cap on. Values were quite different. This time, the exposure compensation was set to 0 and the 20 D read around 25" and the 6D around 2.5" or so. Is this just a difference of the algorithms used against the dynamic range of both cameras (seeing as though the 6D is a lot greater)?

Message edited by author 2014-10-11 09:56:58.
10/11/2014 09:36:46 PM · #2
Sounds like a question you need to be addressing with Canon support. This seems way out of line to me :-(
10/11/2014 10:29:21 PM · #3
Those are wwsome pretty high variances in exposures. Almost 3 stops difference in your first example. Doesn't seem right at all.

What confuses me is that it meters fine in good light.

Probably would give Canon a call.
10/12/2014 12:19:55 AM · #4
Originally posted by PGerst:

Hi. I just got the Canon 6D. Love it. Still fooling around with it and the options since its a pretty decent upgrade from my Canon 20D (also love it).

One thing I noticed is the metering seems a bit off in very dim light.

Given a room that is relatively dark except for some ambient light from the next room. I set both cameras to f4.0 (Tamron 28-75 on the 20D and the Canon 24-105 'kit' lens on the 6D).
Set both cameras to ISO 1600 and metering mode the same (center weighed in this test, although the method didn't matter).
Manual mode.
Picked a dark spot in the room and adjusted the metered exposure to +2.

The 20D metered a shutter of 25 seconds.
The 6D metered a shutter of 4 seconds. Setting 25 seconds provided the correct exposure but was way off the scale.

All other meterings in normal light seem fine, though I haven't done a comparison (will do shortly).

What's up?

Thanks,
Paul

ETA: Just checked something with a bit more light. Same ISO. Metered on same spot. Exposure to +1
20D: 1/5s
6D: 1/13s - 1/15s

ETA: Swapped lenses and picked a different subject. Both cameras metered exactly the same.
Checked with the lens cap on. Values were quite different. This time, the exposure compensation was set to 0 and the 20 D read around 25" and the 6D around 2.5" or so. Is this just a difference of the algorithms used against the dynamic range of both cameras (seeing as though the 6D is a lot greater)?


Can you clarify something please.

You said you are setting the camera to Manual mode....why is the camera choosing the shutter speed? In manual mode YOU chose everything.

Just an FYI some later model cameras and earlier model third party lenses will have issues and firmware on the lenses may need updated.

Matt
10/12/2014 12:25:46 AM · #5
Originally posted by MattO:

Can you clarify something please.

You said you are setting the camera to Manual mode....why is the camera choosing the shutter speed? In manual mode YOU chose everything.

Makes perfect sense to me: he's leaving the apertures constant and changing the shutter speed to center the needle. Camera's not setting anything, HE is.
10/12/2014 12:49:59 AM · #6
Originally posted by Bear_Music:

Originally posted by MattO:

Can you clarify something please.

You said you are setting the camera to Manual mode....why is the camera choosing the shutter speed? In manual mode YOU chose everything.

Makes perfect sense to me: he's leaving the apertures constant and changing the shutter speed to center the needle. Camera's not setting anything, HE is.


Ahh I misunderstood what he said. I thought he was dialing in the exposure compensation to +2, didn't make the connection that he was scrolling the SS until the metered graph was at +2.

10/12/2014 01:29:35 AM · #7
Yeah, I did the arbitrarily. I just fooled around a bit more and got some VERY strange results.

Conditions: Ambient light/very dim
ISO: 1600
f4.0 set for both lenses

Two lenses,
A = Tamron 28-75 f/2.8
B = Canon 24-105 f/4.0

Shutter set so that the meter graph is at 0

20D lens A (Tamron) = 8" Resulting photo was good
20D lens B (Canon) = 2.5" Resulting photo was good
6D lens A (Tamron) = 2.5" Resulting photo was good
6D lens B (Canon) = 1" Resulting photo was too dim. I manually pushed it to 8" and got about what I obtained in the other three instances.

Huh??

ETA:
Found something else. Doesn't explain the lens part above (maybe it does)...

But....new situation. ISO1600, new subject dimly lit.

Through the eyepiece metering: 1" (dark, exposed below 1/2 of the histogram)
Through Live View : 3.2" (properly exposed)

Message edited by author 2014-10-12 03:48:30.
10/12/2014 01:09:20 PM · #8
OK, I set up a little test here:
- Canon 70-200/2.8 IS mounted to tripod and aimed at an indoor surface lit by daylight from windows/skylights
- With Canon 6D set to Av, focused and locked position of lens, set focus to "M".
- Mounted 10-stop ND filter to lens
- Metered with 6D (viewfinder); 25 seconds @ f/4, ISO 100
- Swapped camera body to 5D "Classic"
- Metered with 5D; 25 seconds @ f/4, ISO 100
- Swapped back to 6D, metered in live view. Flashing 30". Increased ISO to 400, now 15". SO live view was telling me that I needed 60 seconds @ ISO 100, or more than an additional stop over standard metering.
- Removed ND filter, re-metered with both cameras. 6D was 1/5s in both normal and live view, 5D was 1/5s.

My conclusion is that for my bodies and this specific lens, the metering between the 5d Classic and the 6D is very close. Live View seems to fail in very low light.
10/12/2014 04:40:13 PM · #9
Same metering mode on both cameras?
10/13/2014 12:31:03 PM · #10
Just finished talking with Canon support. Had them repeat the same test I did and they were able to reproduce it. I have a much more lengthy report I just sent them. Good to know that the viewfinder in very low light (for them at least) was pushing an underexposed shot with respect to the live view.
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