Canon Continuous Mode - different exposures

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JumboJunior New Member • Posts: 1
Canon Continuous Mode - different exposures

I am using  Canon 80D and a Canon 5Dmk2 cameras and I notice the same behaviours with both cameras.

I am using AV mode with the aperture set to F5.6 (happens with other apertures as well).

I select AIServo and high speed drive (in other words continuous shooting).

I am using back button focussing, with the button held down.

When I take pictures of a subject in this mode, I get different shutter speeds between the shots in a kind of a pattern. The first may be 1/1250, the second 1/1000, the third 1/1250 and the fourth 1/1000.

Any ideas why this is happening, I would have expected all of the shots to be the same as the composition and light has not changed between shots (as far as I can tell).

I get the same kind of result if I use single shot mode, and depress the shutter multiple times in quick succession.

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Canon EOS 80D
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IR1234 Senior Member • Posts: 1,142
Re: Canon Continuous Mode - different exposures

Unless theres a fault, the incoming light is changing with a +/-1 stop around 1/500. I would check your metering mode. Something like spot metering will be wild, a little bit of movement can see a big change.

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Enders Shadow Senior Member • Posts: 2,035
Re: Canon Continuous Mode - different exposures

The default behavior of the AF-ON button is to start metering and AF (same as half pressing the shutter release). In AI Servo mode, metering & AF will be constantly adjusting to the scene. (Which makes sense for a moving subject) There's no benefit in holding down the AF-ON button unless you changed the behavior of the shutter release. If you don't want the exposure to change, use AE-Lock.

If you want a more informed response, post some samples with full EXIF data.

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rmexpress22 Contributing Member • Posts: 624
Re: Canon Continuous Mode - different exposures
1

I don't know if you can even do two exposures, but that seems like the camera is bracketing.

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Enders Shadow Senior Member • Posts: 2,035
Re: Canon Continuous Mode - different exposures

rmexpress22 wrote:

I don't know if you can even do two exposures, but that seems like the camera is bracketing.

I thought about bracketing. But the OP mentioned a 4 shot sequence. If bracketing is enabled, the camera should always fire off a burst of 3 shots. As long as it isn't in One Shot mode.

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Phil

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karl mohr Senior Member • Posts: 1,569
Re: Canon Continuous Mode - different exposures

Not sure about the 80D, but the 70D can bracket 2,3,5, or 7 shots.  So it is possible that it is set to bracket sets of 2.  Hence the  1/1250, 1/1000 over and over.

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Sailor Blue
Sailor Blue Forum Pro • Posts: 13,243
Re: Canon Continuous Mode - different exposures
2

1/1000 sec and 1/1250 sec are only 1/3 of a stop apart.

Exposures are measured to ±1/6 stop and then rounded off to the nearest 1/3 stop.

My guess is that the actual exposure is somewhere between 1/1000 sec and 1/1250 sec and small variations in how the camera is pointed are enough to change the measured exposure enough to cause the calculated shutter speed to change between those two values.

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Enders Shadow Senior Member • Posts: 2,035
Re: Canon Continuous Mode - different exposures

Yeah, I forgot about that. The number of shots in a bracket sequence is also configurable on the on the 80D. But if using one of the continuous drive modes, the camera will shoot that number of images then stop if the shutter is held down long enough. Possibly the OP is trying to shoot a short burst and the sequence didn't complete. I'm starting to think they have bracketing enabled. Default setting has bracketing cancelled when the camera is turned off, but that also can be changed.

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rdspear Veteran Member • Posts: 4,554
Re: Canon Continuous Mode - different exposures
2

1/1000 and 1/1250 are adjacent shutter speeds.  It's possible the lighting is just on the margin between the two of them and evaluating minutely different each time.  Some lighting strobes at a speed too fast for the human eye to see but enough to affect electronics.  Minute camera movements, electric current variations, etc., can all add up to the tiny variation to push over and back of the demarcation between the two shutter speeds.

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MarshallG
MarshallG Veteran Member • Posts: 6,121
Fluorescent Lights

rdspear wrote:

1/1000 and 1/1250 are adjacent shutter speeds. It's possible the lighting is just on the margin between the two of them and evaluating minutely different each time. Some lighting strobes at a speed too fast for the human eye to see but enough to affect electronics. Minute camera movements, electric current variations, etc., can all add up to the tiny variation to push over and back of the demarcation between the two shutter speeds.

Perfect explanation.  And if any lighting nearby is fluorescent... this can also happen.

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wave01 Regular Member • Posts: 402
Re: Fluorescent Lights

I have just checked my 7d2 with a few burst shots and the exposure doesn't change. That said the light hasn't changed either

Imajica Regular Member • Posts: 236
Re: Canon Continuous Mode - different exposures

I had this problem with I my 70-200 f2.8,  I had to send the lens in for repair.  The problem was with the lens.  It was the shutter assembly (or whatever it was called) in the lens that needed to be replaced.  Cost $600 too fix.

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rdspear Veteran Member • Posts: 4,554
Re: Canon Continuous Mode - different exposures
1

Interesting. Aperture blades not retracting quickly enough and reducing light during the AE evaluation? I hadn't heard that before - one to store away in the memory banks.

Seems odd it would also happen with single shots - would have to be a mighty slow return and a very fast finger. Also odd it would oscillate. I would think the 2nd and subsequent images would be all similarly mis-evaluated. And the shutter speed should decrease not increase.

But an interesting new hypothesis to look at.

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John Sheehy Forum Pro • Posts: 20,466
Re: Canon Continuous Mode - different exposures

JumboJunior wrote:

I am using Canon 80D and a Canon 5Dmk2 cameras and I notice the same behaviours with both cameras.

I am using AV mode with the aperture set to F5.6 (happens with other apertures as well).

I select AIServo and high speed drive (in other words continuous shooting).

I am using back button focussing, with the button held down.

When I take pictures of a subject in this mode, I get different shutter speeds between the shots in a kind of a pattern. The first may be 1/1250, the second 1/1000, the third 1/1250 and the fourth 1/1000.

Any ideas why this is happening, I would have expected all of the shots to be the same as the composition and light has not changed between shots (as far as I can tell).

I get the same kind of result if I use single shot mode, and depress the shutter multiple times in quick succession.

You're on the meter's cusp. It's affect is not analog; just shifting the camera a little or a tiny change in the lighting of 1/10000000 stop can toggle between the two of the camera's coarse 1/3-stop shutter speed values. Of course, this can make some images almost 1/3 stop apart in apparent brightness. You avoid this by using manual mode, or exposure lock (which I haven't tried recently, so I don't know how that works).

Why doesn't the camera have nearly virtual analog Tv values (or auto-ISO values)? That's a good question. There is some benefit to the quantized Tv/Av product, though, as slight changes in composition may fail to change needed exposure, which may be ideal. Either approach has its problems, and different circumstances benefit from different methods.

If the light source is not steady and is strobing quickly, then it is difficult to meter for unless the camera has anti-flicker intelligence and can see the pattern and always expose at the same light phase, but that can't help with every situation, especially with fast shutter speeds which may cause the exposure to be different and the light color different, up and down the frame, even if consistent between frames. If you are using a two-curtain focal plane shutter, any "shutter speed" above your normal flash sync speed on that camera is basically fiction. The shutter is never fully open for as little as 1/1250 second; a slit of open curtain a fraction of the height of the frame passes over the sensor vertically, over a period several times the 1/1250s.

Imajica Regular Member • Posts: 236
Re: Canon Continuous Mode - different exposures
1

Took me a while to figure it out, but in my case i noticed it only happened on one lens regardless of what body it was hooked up to.  Generally it was more noticeable when doing burst shots. However it did happen on single shot as well.  The first shot would usually be ok, but then the exposure would jump all over the map.  Under exposed, over exposed, just right.  At first it was not a big deal.  I just thought the lighting changed slightly but after a week or 2 it was getting more and more pronounced. I had my lens since 2004 and put at least 500k photos on it/ I guess the aperture blades have a lifespan just like a shutter in the camera.

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