Strange overspec metering results with Canon 5D Mark III

[duydaniel]

Did you set the Auto ISO limit at 4000? I didn't see anyone ask this question.

Someone did ask, but I don't think that's the issue - the min/max for the ISO range is set in whole-stop increments, ISO 3200 or 6400, but 'tweener' stops can't be set.

on 5D3 the auto iso can be in between "full stop" iso
such as iso 3200-4000-5000-6400 etc

 

[Loswr]

Did you set the Auto ISO limit at 4000? I didn't see anyone ask this question.

Someone did ask, but I don't think that's the issue - the min/max for the ISO range is set in whole-stop increments, ISO 3200 or 6400, but 'tweener' stops can't be set.

on 5D3 the auto iso can be in between "full stop" iso
such as iso 3200-4000-5000-6400 etc

Of course it can (in fact, with Auto ISO there's no way to not have it use the tweener ISOs, even if you want that). But my point is that the maximum ISO limit cannot be set to an in between value, only to full stop increments. The issue that the OP mentioned was the camera selecting ISO 4000 as the exposure got darker and darker, and since that's a tweener value, a setting that limits the ISO to a max 4000 isn't a viable explanation, since it's not possible to set such a limit, only ISO 3200 or 6400 could be set.

 

[Teemu76]

Did you set the Auto ISO limit at 4000? I didn't see anyone ask this question.

Maximum auto ISO limit was 12800. I think I managed to prove that whole point about camera not selecting ISO values above was limit in metering system. In this case exposure value was EV -3 (1.6s, F2.8, ISO 4000). With F4 lens that limit was EV -2 and with F1.4 lens limit was EV -5. So it seemed that limit for camera metering was EV -6 with theoretical F1.0 lens and less with dimmer lenses. Each stop of lens brightness drops maximum meterable exposuer by one stop.

Reference for calculation of exposure value:
http://en.wikipedia.org/wiki/Exposure_value

 

[duydaniel]

max auto iso is 25k on 5d3
you need to set it

Did you set the Auto ISO limit at 4000? I didn't see anyone ask this question.

Maximum auto ISO limit was 12800. I think I managed to prove that whole point about camera not selecting ISO values above was limit in metering system. In this case exposure value was EV -3 (1.6s, F2.8, ISO 4000). With F4 lens that limit was EV -2 and with F1.4 lens limit was EV -5. So it seemed that limit for camera metering was EV -6 with theoretical F1.0 lens and less with dimmer lenses. Each stop of lens brightness drops maximum meterable exposuer by one stop.

Reference for calculation of exposure value:
http://en.wikipedia.org/wiki/Exposure_value

 

[Teemu76]

max auto iso is 25k on 5d3
you need to set it

Did you set the Auto ISO limit at 4000? I didn't see anyone ask this question.

Maximum auto ISO limit was 12800. I think I managed to prove that whole point about camera not selecting ISO values above was limit in metering system. In this case exposure value was EV -3 (1.6s, F2.8, ISO 4000). With F4 lens that limit was EV -2 and with F1.4 lens limit was EV -5. So it seemed that limit for camera metering was EV -6 with theoretical F1.0 lens and less with dimmer lenses. Each stop of lens brightness drops maximum meterable exposuer by one stop.

Reference for calculation of exposure value:
http://en.wikipedia.org/wiki/Exposure_value

Maximum value for auto ISO upper limit is 25600 but I used 12800 as maximum value. Limiting factor was not auto ISO but exposure metering system limitation. This was actually positive finding because camera went way beyond specified metering range.

 

[hwoarang5]

simplest way.... get a good lightmeter...

 

[bvukich]

simplest way.... get a good lightmeter...

For one shot, yes. For a timelapse, that wouldn't help him much.

 

[bvukich]

I haven't played with the exposure ramping in ML, can it ramp with ISO instead of Tv/Av? I know it doesn't directly address your issues with metering at extremely low light levels (and an ND... eek) but it may achieve your goal of a smooth timelapse.