Coming from a DSLR background, many shooters have a similar procedure for exposing their image: Shutter 1/50th, ISO low as possible, ND and aperture to suit.
However implementing this method on other cameras can be detrimental to your image. The Canon C100/C300 has a base ISO of 850, use this for best results.
It may be a simple and obvious procedure for some, but having met quite a few shooters over last few months that weren’t aware of this, I felt it worth writing a quick article on.
The native ISO on both the Canon C100 and C300 cameras is 850; anything below or above this is compensation. Unlike shooting raw, raising the ISO in-camera is still a critical point of exposing the 8-bit internal codec of the Canon cameras, however it is the reduction of ISO speeds that I want to talk about.
It is best to present this in the form of screen shots, here below is an image taken from my C100 (out of my window quickly so nothing award winning or scientific), as you can see by the overlays I am using an ISO of 850 and an aperture of f/5.0 with 6 stops of ND. My shutter is 1/50th and my picture profile Cinema EX (I choose not to display these overlays to keep the screen display clean).
It’s a dramatic shot in terms of dynamic range, but you can see cloud detail, and highlight peaks are limited. I’ve added a waveform overlay from Premiere Pro on the right hand side so you can see what’s happening with the information.
Here’s the same shot, but using a lower ISO of 320; this is typically how you would approach exposure with a 5D mark iii for example. I’ve compensated for exposure by reducing the ND to 4 stops, and opening the aperture to f/4.0.
In terms of exposure these settings should be fine, but look at the waveform, it’s flat lining before the top of the graph.
So what’s different? With the latter setup, you are letting more light hit the sensor by reducing physical attributes which affect exposure – ND and aperture. As the ISO level of 320 is over a stop lower than the base level of the sensor (which is 850), the sensor can’t handle it and is losing information in the highlights, despite on paper the settings being within the range of correct exposure.
Just look at the cloud detail for proof, all information is gone and what’s left is a grey mess.
By shooting with the native ISO of 850, you are using the base level of sensor, any exposure adjustments are physical ones (aperture and ND) which stop/allow light from hitting the sensor. Canon has kindly set a reminder in the overlays by adding brackets around ISO 850 so you don’t forget.
Stick to ISO 850 as much as you can; I never dip below it. In lowlight situations I’ll raise to dependant on situation, this does not have the same detrimental effects; you can raise the ISO above 850 should you require (just be aware that the higher your ISO rises, so does the amount of noise present within the image).
This is not a procedure restrained to the Canon C100 and C300 cameras, the Sony F55 works on a base ISO of 1250, and the A7S 3200. The difference in these cameras are that when operating in S-Log modes, you physically can’t reduce the ISO levels below its native setting; quite a handy feature when you consider what your image can end up like if you were to simply exposure without consideration for the base ISO of your camera.