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  • Hey all, just changed over the backend after 15 years I figured time to give it a bit of an update, its probably gonna be a bit weird for most of you and i am sure there is a few bugs to work out but it should kinda work the same as before... hopefully :)

2K cropping confusion

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Bryce Lansing

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Hey guys, I apologize for all of my dumb questions. I'm very new to the Red, and am trying to learn as much as possible about it before I use it.

I understand that in 4k you can only shoot up to 30fps, and that if I wanted to overcrank, I'd need to shoot at either 3k or 2k.

But if I shoot in 2k, is it really cropping the frame to about that of a 16mm film frame, taking away angle of view from each lens, and causing deeper DOF?
 
same dof by using the same lens

same dof by using the same lens

mrbrycel said:
Hey guys, I apologize for all of my dumb questions. I'm very new to the Red, and am trying to learn as much as possible about it before I use it.

I understand that in 4k you can only shoot up to 30fps, and that if I wanted to overcrank, I'd need to shoot at either 3k or 2k.

But if I shoot in 2k, is it really cropping the frame to about that of a 16mm film frame, taking away angle of view from each lens, and causing deeper DOF?
Click to expand...

When you use the same lens in 4K,3K and 2K the DOF stays the same, you are only using a smaller part of the sensor. Smaller use of sensor faster speed.

regards
Robert R 1265
 
When you change from say 4K on a 24mm lens to 2K on the same lens, you use less of the sensor. The frame you then get at 2K obviously appears "zoomed in" - to roughly double the focal length of your lens, so a 24mm at 2K would roughly look like you were wearing a 50mm at 4K. Obviously the DOF does not change as you are on the same lens, with the same stop.

tom turley
www.filmtom.com
 
mrbrycel said:
But if I shoot in 2k, is it really cropping the frame to about that of a 16mm film frame, taking away angle of view from each lens, and causing deeper DOF?
Click to expand...

yes
 
Thanks guys! Is it uncommon or bad to mix 2K and 4K footage? If you wanted the best results, but had a few shots you needed to overcrank, would the overcranked 2K or 3K shot. Cut together with the 4K shots look different?
 
mrbrycel said:
Thanks guys! Is it uncommon or bad to mix 2K and 4K footage? If you wanted the best results, but had a few shots you needed to overcrank, would the overcranked 2K or 3K shot. Cut together with the 4K shots look different?
Click to expand...

there is a quality difference, but people intercut it all the time. if you need the BEST quality, rent a Phantom for your slo-mo shots, bur otherwise don't worry about it :)
 
If you're overcranking for a shot, it's usually for effect, and viewers are noticing the effect more than a drop in resolution. Intercutting is fine.
 
Many overcranking needs can be served with 3K as opposed to going to 2K. And 3K still has sufficient resolution to deliver a sharp 2K/1080p image. But ericyoung is right, intercutting for some FX shots is usually OK. More so than the resolution, people typically notice changes in FOV or apparent framing, so keep that in mind when creating all your other shots to work with the 2K shot.

When shooting 3K or 2K, it is the equivalent of shooting 4K and then cropping out the 3K or 2K portion of the center of that image. DOF does not change. DOF is a property of focal length and aperture diameter and how they relate to focal distance. Let's say the DOF is 13" at F2.8 on a 100mm lens with the focal point 15ft. away. That DOF does not change, it's always 13" at those distances and aperture size, regardless of whether you are shooting 4K, 3K, 2K, whateverK.

Like I said, it is the Field Of View that changes. So if you frame a shot in 4K with that lens, your FOV width would be about 40" wide at the focal plane and the DOF would be 13". If you were to change nothing, other than to switch the camera to 2K, your FOV width would now be 20" wide as you are just cropping the image area and DOF would still be 13". To recreate the same framing with 2K that you had with 4K, you must now move the camera back from 15ft of the subject to 30ft of the subject. This will give you a 40" wide FOV when in 2K with your subject at 30ft.

Now that you have the same framing for 2K that you had for 4K, you can calculate DOF based on the 30ft. distance. Uh, oh... at 30ft, with this lens, the DOF is now close to 28" or more than twice as deep as it was at 15ft.

At this point, if you want to match DOF between the two shots, you will have to open up the aperture by 2 stops or so... If possible.
 
I'm shooting a music video which will mostly play on TV, the highest possible end result needed would probably be 1080 for a blu-ray. I'm thinking my highest frame rate may only need to be 60fps, so I'll probably shoot that in 3K.

Also, I come from the 35mm photo/HD camera with 35mm adapter world, so I'm used to the focal lengths in relationship to 36mm x 24mm. What is a "normal lens" for the mysterium sensor at 4K?
 
What do you consider a normal lens to be for 36mm x 24mm? 4K is about 22.2mm wide and 3K would be about 16.6mm wide. So if you are matching horizontal view, it's a 1.6X factor for 4K and a 2.2X factor for 3K.

So if you feel a 50mm lens is "normal" for 36mm x 24mm, then that's 31.25mm (round up to a 35mm lens) for 4K and 22.7mm for 3K (round up to a 24mm lens).

You should be able to figure this stuff out yourself with a calculator... the dimensions of the RED sensor are published (4520 x 2540 pixels on a 24.4mm x 13.7mm sensor / 4K recording is 4096 pixels wide), so it's not very hard to figure out.
 
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