RED Epic – Crop Factor at Various Resolution Settings

Right out of the gate, I apologize for getting a bit off topic in this post. It’s all relevant to the headline but I also explore a few reasons why to crop/not crop in addition to providing a side-by-side comparison video and a normal video 1920×1080 frame size that cycles through the crop factors.  It was shot with a 50mm RED Pro Prime lens and the camera was not moved between shots, I simply went into the menu and changed resolutions. Here are the videos:
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When the Canon 5D Mark II was released around 2008 followed soon after by cropped sensor cameras that could also shoot video, like the Canon 7D, lens/sensor crop factor became a real thing that cinematographers now needed to be aware of.  Still photographers had been aware of crop factor for a long time, but it was a fairly new concept for people shooting motion.

 

With digital still photography cameras now offering video, two completely different worlds collided causing a whole lot of math to be forced onto us creative folk and also a whole lot of confusion about crop factor. By using 35mm full frame coverage glass on a camera that had a smaller sensor, the focal length effectively changed and other limitations like getting wide angle shots became a bit more challenging.

 

I’m not going to get into too much detail on DSLR crop factors as this is a post to simply show what happens to the field of view in a RED Epic when you switch resolutions. Switching resolutions results in big changes to your field of view and also the look of the background elements.

 

The thing that bothers me the most about crop due to a resolution change when shooting on RED is that the focal length of the lens now means almost nothing. A 24mm lens will no longer produce the look of a 24mm lens so our creative thinking has to completely change. Also, it gives a different aesthetic to the background than might be intended by the DP.

 

Now I realize some of you reading this may not understand what I mean by a 24mm looking like a 24mm lens. Many people simply use a wide angle lens to have a wider field of view to fit more stuff in the frame. Wide angles are also used for creative reasons to exaggerate things like facial features or camera moves, particularly camera moves that push in or pull away quickly. And on the other end of the spectrum a telephoto lens is not the same as cropping into a shot captured on say a 50mm lens.

 

Yes, we might be able to achieve the same framing and same relative size of the talent, but the talents face and background elements will look completely different if you shoot on longer lens instead of zooming either by cropping the sensor or in post afterwards.

 

I want to point out right away that ideally, in a perfect world when shooting on a RED format, it is always be best capture the scene at the highest resolution in the aspect ratio of your required or chosen delivery. There are many advantages for this.

 

One big advantage is that your lenses will perform closer if not exactly to how they were designed to perform, meaning a 24mm will look like a 24mm.

 

Another advatange, which is always true in my case, is that I’m never delivering anything larger than 1920×1080 or in some cases 2048×1080 for theatrical release. I mention this because as you’ll see in the video, when the resolution is lowered the image is effectively zoomed in. This may be something you are looking for in your shot if perhaps you don’t have long enough glass to get the composition you are looking for but the same thing can be achieved with more flexibility in post production assuming your delivery format is smaller than the resolution you are shooting as it is often the case for me. In this example, let’s say you shoot in 5K and deliver in 1080. You will have a ton of room to recompose the shot.

 

I have to make clear though, generally speaking, recomposing a shot in post should be used to fix a problem like a boom in the shot or for stabilization of a shaky take. I say generally because who am I to tell you how to create your art. All I’m getting at is that it shouldn’t be used as a way of being lazy by not changing lenses because you can “push in in post”.

 

I know many people reading this will have loads of opinions and arguments on why you should shoot a smaller resolution and I will mention a few very valid reasons that I use myself sometimes.

 

One big one if post production workflow. Even as awesome as computer systems are these days, a higher resolution will definitely put a squeeze on your workflow. Even if the 5K footage plays back smoothly on your system, once you perform normal post production tasks like adding effects and color correction, your system will start to bog down, making it very difficult to stay in a creative flow. Yes there are work arounds like viewing at lower resolutions will editing and even digressing into an offline edit workflow. These are just fine if you have the time for offline/online and are ok with rendering out things like effects to get realtime playback.

 

Another reason to shoot lower resolution is to have more recording time on the media card. Definitely a valid reason in many cases.

 

Yet another reason, is if you have to hand off the footage to someone else for post or if the turn around time for the edit is really quick. Both of these things could even turn into a consideration to send the signal out to an external recorder and capture a 1920×1080 ProRes file. I actually think I would ideally keep my RED set to the highest resolution, keeping my lenses and field of view normal, and send a feed to a ProRes Recorder for 1080 capture. You will not only save time in the edit, you will also save time transferring footage to a drive to do a hand off. Again, this is something I consider for really quick turn projects.

 

A final reason to record at a reduced resolution is to unlock faster frame rates in the camera. This used to be the main reason a DP would downsize in resolution but as of the latest RED releases (Dragon etc) the frame rates are pretty damn high even at 5k. As of this writing, RED Dragon can do 96 fps at 5K and 120fps if you go widescreen. For most applications thats pretty good!

 

Ok, I have totally gone off topic as I knew I would. I hope you found this useful. The RED website also gives you a handy tool to see how crop factor will affect your shot. It’s found here: RED Tools

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