Which of these 3 cameras is best, any geniuses out there?
To make it simple we're looking for a camera to shoot videos. The most important thing for us is a shallow depth of field - not just for close up footage i.e. flowers - but for full body video shots i.e. the subject would be entirely clear in focus and the background blurred.
I know there is a strong correlation between aperture / focal length / sensor size, but I am still unsure.
Can anyone here tell me which of these 3 cameras would be BEST and if possible WORST for the above goals.
Hey David, first a caution. I think what you are really after is a "cinematic" look to your footage. And yes, shallow depth of field is one very often cited aspect of the "cinematic look" but it's only one and a lot of other things go into a movie-like shot versus the "video" look that so many of us want to avoid.
But since you asked about shallow depth of field specifically here are the general things you want to look for:
* Think about getting as much light into the sensor as you can, so cameras with a larger sensor - like APS-C, Super 35, and "full frame" - Shallow depth of field is possible with the Micro 4/3rds cameras too that have slightly smaller sensor, the camera and operator just has to work a bit harder. Larger sensor cameras tend to be the more expensive one's unfortunately.
* Now here's the real key: the "faster" the lens on the camera the better - faster meaning it has a very "low" aperture number, like 1.8, or 1.4 or 2.0 versus say an aperture of 8.0 which isn't considered fast at all but "slow."
So when you look at the aperture on the lens I'd say go for anything 2.8 or lower with 1.8 or 1.4 being a very nice sweet spot. Keep in mind too that focus is more difficult to achieve and maintain when shooting very very shallow. In fact, it's possible to focus on the nose of an actor and have their eyes be out of focus if you are filming with extremely shallow depth of field. Imagine if they are moving - how much harder that gets.
There are some great examples of entry level lenses that are relatively inexpensive and still have aperture values that are way down there (I mention one or two from Canon down below)
Speaking of apertures ideally you want a lens that has a constant aperture. If you look at a lot of zoom lenses for instances, particularly those that come as "kit" lenses, they will have a RANGE of apertures, in other words as you zoom in and out the aperture actually changes. So you zoom in on a subject and the picture darkens, this throws many shooters for a loop the first time they see that.
For this reason, "prime lenses" that have only one focal length and one aperture are ideal, like the Canon 50mm 1.4 or their 50mm 1.8 just to give a quick example.
* If you plan on filming outside and want to maintain that shallow depth of field, then you can easily find yourself in a situation with TOO much light hitting the sensor - to the point where adjusting the ISO won't solve the problem, even lowering the ISO and in addition bumping up the aperture to a higher number isn't enough to solve it.
In those situations technically you could adjust the camera's shutter speed to some very high value and while that technically will cut down the light the resulting video will probably have a very non-cinematic look that you won't like at all.
So what do you do??? You either film in a shadier spot, get the actors under some diffusion material or you do like I do and get yourself some ND filters that knock down the light hitting the sensor, allowing you to keep a wide open aperture, low ISO, a 1/50 shutter speed AND get that shallow depth of field look. Easy Breezy right???