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Archie Campbell

ISO sensitivity on C300

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Hi guys,

 

I was wondering if anyone could explain to be the discrepancy between the ISO sensitivity I have seen on some tests involving the C300.

 

How come when compared to DSLR's ISO 20,000 seems to be about the same sensitivity as ISO 6400 on the DSLRs?

 

Is the ISO standard not a constant?

 

Thanks.

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You do get variations in sensitivity when you use different gammas and curves. The cameras here have different curve set ups, so they're not absolutely comparing like with like. How the log curve affects the C300's sensitivity needs to tested, but sensitivity does change on other cameras when you use different curves on the camera. Although, if given a ISO you do expect the camera to make internal adjustments - most video cameras don't give ISO figures you need to test the camera to find out. So maybe the C300's ISO only refers to when you're using a certain curve or picture profile in the camera.

 

Another possibly is incorrect data in the on screen titles either in the ISO or the f stop being used, since they also say in the text "Same settings, same f-stop, similar ISO setting etc".

Edited by Brian Drysdale

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Which tests are you referring to?

 

See paul's post

 

Are you referring to this test http://vimeo.com/33452552

 

Yes, that's the test I am referring too. It's the fact that the original uploader mentions in the comments that 20,000 ISO is equal to 6,400 ISO on the 1div.

 

You do get variations in sensitivity when you use different gammas and curves. The cameras here have different curve set ups, so they're not absolutely comparing like with like. How the log curve affects the C300's sensitivity needs to tested, but sensitivity does change on other cameras when you use different curves on the camera. Although, if given a ISO you do expect the camera to make internal adjustments - most video cameras don't give ISO figures you need to test the camera to find out. So maybe the C300's ISO only refers to when you're using a certain curve or picture profile in the camera.

 

Another possibly is incorrect data in the on screen titles either in the ISO or the f stop being used, since they also say in the text "Same settings, same f-stop, similar ISO setting etc".

 

I'm still confused as surely this puts everything I have learnt with my light meter sort of useless if there can be a 2 stop difference in ISO between cameras?

 

Any idea as to which camera (C300 or 1div) is likely to have the more correct ISO and therefore I can compare to the cameras I have used?

 

Thanks for the help guys!

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I'm still confused as surely this puts everything I have learnt with my light meter sort of useless if there can be a 2 stop difference in ISO between cameras?

 

Any idea as to which camera (C300 or 1div) is likely to have the more correct ISO and therefore I can compare to the cameras I have used?

 

Thanks for the help guys!

 

It looks like this may cause confusion because they're using an ISO rating, rather than using gain settings for increasing sensitivity. I'd expect the ISO of a camera to be lower when using a log curve rather than when using a more standard rec 709 setting, but it seems that Canon may possibly not be putting in an adjustment to the ISO when using the log curve.

 

If the camera isn't internally doing this, there will be non log curves or picture profiles in the C300 where the ISO displayed is correct. In these settings the camera ISOs should match up, but not seemingly on log - at least on these pre production cameras.

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Just as a follow on, people are using a number of exposure setting methods on the F3 when using s-log so as to ensure the best dynamic range.

 

One of which is to use an exposure meter. I suspect you'd have to do some tests with a chart to find out the optimal ISO to set on your meter, ignoring whatever ISO the C300 says and using the sensitivity setting that gives the best dynamic range on the C300.

 

Another is to use a chip chart, with the mid grey at 38% and whits 68% - this could be wasteful if there are no highlights above 68%. Then you can use the waveform monitor or a histogram.

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Thanks for the info Brian!

 

I'm sure that once the C300 is out there will be quite a few tests done.

 

There is a setting in the camera {EOS Std) that's supposed to match a EOS DSLR with its picture style set to standard, that might be a more direct comparison for high ISO sensitivity, rather than log which is more about getting the best dynamic range for grading in post. Although, you probably wouldn't want to push the 8bit images too far if you want the best results.

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Speaking practically, I can't think of a single cinematic use of 20,000 that 6400 wouldn't handle save for exposing by the light of the moon.

 

 

6400 was good enough for the FBI, and they don't have lights to point at suspects (at least in the visible spectrum). I can't think of any situation I'd need to light with a requirement for more than ISO 1000, unless we want to shoot "Citizen Kane" style with a stopped-down zoom.

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Speaking practically, I can't think of a single cinematic use of 20,000 that 6400 wouldn't handle save for exposing by the light of the moon.

 

I can only think of a handfull of occasions where I've wanted more than say 1,500 ISO, but they're all documentary or current affairs and I didn't want to use any lights. Perhaps wild life work is the most likely use of the 20,000 ISO shots.

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I'm still confused as surely this puts everything I have learnt with my light meter sort of useless if there can be a 2 stop difference in ISO between cameras?

 

Maybe it would be better to not use alight meter and instead expose for the highlights you don't want to lose, especially using a gamma that's designed to be graded and not look 'right' straight out of the camera.

A light meter tells you where middle gray is which doesn't really matter very much does it?

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I can only think of a handfull of occasions where I've wanted more than say 1,500 ISO, but they're all documentary or current affairs and I didn't want to use any lights. Perhaps wild life work is the most likely use of the 20,000 ISO shots.

 

I agree with the value this camera would have for documentary shooting, Brian, but I did say "cinematic" as in dramatic filmmaking, Shooting a herd of antelope by the light of the moon in the African Savannah I'm sure could benefit from high ISOs.

 

 

Then again, I doubt this camera is the type whose price range is going to fit that sort of production, even for rentals. You don't see many Panavisions out in the jungle for years on end, either. :-)

 

 

As for "1500" is that more along the lines of 1250 or 1600? As this may be the first high-speed digital device to ever get the high-ISO numbers RIGHT, you shouldn't jinx it by making up your own ISOs (see Canon's 204,800 thugliness). :P

 

If you own a DSLR, I give you a pass. I know their prime audience is a bunch of computer nerds who love odd base-2 numberings, but for those of us who actually seek income, give us a break!

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If you own a DSLR, I give you a pass. I know their prime audience is a bunch of computer nerds who love odd base-2 numberings, but for those of us who actually seek income, give us a break!

 

LOL I was thinking in the video land of dbs at the time and doing a rough conversion, in film land I've gone up to 2000 ASA with 16mm reversal - definitely grainy and not something for dramas, at least not unless you want the effect.

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the test was too rough for me, need more details and setup.

 

even after scarlet and c300 i still keep leaning toward an f3, maybe cuz i'm an ex1 user...

 

btw, i see no excuse for 20,000iso except in extreme circumstances, which i can hardly imagine a $15,000 camera would be in. when you can get an led light and a light stand that you can throw in your case to get that little extra splash of fill on a face, ISO bumps will never be the proper choice

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What is meant by ISO BASE SENSITIVITY. They say like f3 or c300 iso base sensitivity of 800.

 

Often it's the ISO setting that gives the best dynamic range.

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also in terms of noise, it's their native sensitivity, bumping it down won't yield miles less noise, and bumping it up will start to add noise. think of it as 0 gain

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