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R5 Inconsistent auto ISO bracketing exposures

yellowalien
Contributor

Camera is set up for auto ISO bracketing (change EV by adjsting ISO instead of shutter speed or f/stop): exposure mode is M with e.g. shutter speed to set e.g. 1/200 s and aperture at f/8. ISO is set to auto ISO (auto ISO range set to 100-6400).

 

Occasionally I see inconsistent exposures, i.e. two or three exposures that look almost identical in EV, then a jump that looks like more than +1 EV (more like +2 EV) when compared to the previous exposure. I have had a suspicion that this odd behavior might occur near the limits of the auto ISO range.

 

When using bracketing with shutter speed the exposure brackets look ok.

 

Has anyone seen this?

9 REPLIES 9

rs-eos
Whiz

What is the ISO value you are setting for your middle/standard exposure? 

--
Ricky

EOS 5D IV, EF 50mm f/1.2L, EF 135mm f/2L, 600EX-RT (x6), ST-E3-RT
EOS C70, RF 24-70 f/2.8L IS, EF-EOS R 0.71x

The camera has firmware 1.3.1.

 

Looking at a specific example:

 

EV -3: f/8 1/640 ISO 200

EV -2: f/8 1/320 ISO 200

EV -1: f/8 1/250 ISO 320

EV 0: f/8 1/250 ISO 640

EV +1: f/8 1/250 ISO 1250 

EV +2: f/8 1/250 ISO 2500

EV +3: f/8 1.250 ISO 5000

 

Exposure #5 (EV +1) looks identical (visually) to exposure #6 (EV +2).

 

Therefore exposure #5 appears two stops brighter than exposure #4.

 

 

 

So the metadata being reported for the EV+1 and EV+2 both show f/8 1/250 and just the difference being in ISO?   I'm assuming no flash is being involved.

 

What happens if you put the camera on manual, take one expsoure at f/8, 1/250, ISO 1250 and a second exposure at ISO 2500?  Same problem? Or only when bracketing is involved?

 

 

--
Ricky

EOS 5D IV, EF 50mm f/1.2L, EF 135mm f/2L, 600EX-RT (x6), ST-E3-RT
EOS C70, RF 24-70 f/2.8L IS, EF-EOS R 0.71x

I'll see whether I can reproduce the problem, and then follow up with manual exposures to go along with it, but as I said, I only see the problem sometimes. The example above was out in the field three weeks ago on an overcast day in the park. 

 

BTW, the next sequence that day also has exposure #5 too bright, but the sequence immediately after had the exposure #6 too bright (same appearance as exposure #7).

 

EV -3: f/8 1/640 ISO 200

EV -2: f/8 1/320 ISO 200

EV -1: f/8 1/250 ISO 320

EV 0: f/8 1/125 ISO 320

EV +1: f/8 1/125 ISO 640 

EV +2: f/8 1/125 ISO 1250   <-- too bright

EV +3: f/8 1/125 ISO 2500

 

Seems I dropped the shutter speed by one stop to achieve a lower ISO (for the third sequence).


@yellowalien wrote:

I'll see whether I can reproduce the problem, and then follow up with manual exposures to go along with it, but as I said, I only see the problem sometimes. The example above was out in the field three weeks ago on an overcast day in the park. 

 

BTW, the next sequence that day also has exposure #5 too bright, but the sequence immediately after had the exposure #6 too bright (same appearance as exposure #7).

 

EV -3: f/8 1/640 ISO 200

EV -2: f/8 1/320 ISO 200

EV -1: f/8 1/250 ISO 320

EV 0: f/8 1/125 ISO 320

EV +1: f/8 1/125 ISO 640 

EV +2: f/8 1/125 ISO 1250   <-- too bright

EV +3: f/8 1/125 ISO 2500

 

Seems I dropped the shutter speed by one stop to achieve a lower ISO (for the third sequence).


Not a problem that I can see in the numbers.  BTW, if EV +2 is too bright, then why isn't EV +3 a;so too bright?

 

Why are are using ISO to bracket exposures, instead of shutter speed, anyway?

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"The right mouse button is your friend."

When I wrote "too bright", I meant to say, too bright for EV +2 (it appears identical in brightness as EV +3, which I think has "proper" brightness for EV +3 in the example). If you read the first post, the "improper" or too bright" frame isn't always the same.

 

As you should know, bracketing the shutter speed has implications on motion (blur). But this is beside the point as I am using (or intending to use ISO bracketing.

 

Maybe I can do some more testing on Sunday, but I have only seen this behavior with auto ISO bracketing so far. I expect manual bracketing to produce "proper" EV -3 .. EV +3 exposures.

 

Seems nobody has experienced this problem

Because people prefer motion blur over noise, I guess.

When bracketing though, it's much easier to composite images when any movement is at a minimum.

 

It probably wouldn't matter though depending upon the subject if the shutter is say 1/250 or quicker.   It would though be problematic to composite certain subjects with 1/30 through 1/500 shutter.   You'd end up with much larger areas of movement and that can lead to very poor compositing results.

 

What I personally do if I can, is bracket with flash power.  Here, aperture, shutter and ISO are now constant.

--
Ricky

EOS 5D IV, EF 50mm f/1.2L, EF 135mm f/2L, 600EX-RT (x6), ST-E3-RT
EOS C70, RF 24-70 f/2.8L IS, EF-EOS R 0.71x


@kvbarkley wrote:

Because people prefer motion blur over noise, I guess.


What motion blur?  Normally, you're not trying to capture a bracketed shot of a moving subject.  Isn't a bracketed shot supposed to be that of a static subject or scene?

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"The right mouse button is your friend."
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