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18-50mm at 2k = 36-100mm?

James Page

James Page

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Hi,

When inquiring after a longer lense I've been told by a hire company that if i shoot at 2K the standard PL mount 18-50mm lense becomes, in effect, a 36-100mm lense.

Firstly is this true, and if so can someone explain to me why?

secondly, is there an online resource of different stills from RED footage with their metadata intact, for study and comparison?

Much appreciated in advance.

Best

Jim
 
Hi

Firstly, thanks for replying. I'm not the DP, so the links you gave me, whilst I'm very grateful, are kind of like Chinese to me!

I just want to know that we can achieve the long lense/ shallow DOF look we want on the shoot with the equipment we have, and this hire company person tells me that shooting at 2k will, in effect, make the lenses longer/ decrease the focal length. With my limited knowledge I don't really understand why he said this however, so I firstly want to confirm or deny it, and if its true, if you could provide some information that's a bit more of an overview, or visual, I'd really appreciate it!

Feel free to talk to me like a stupid person!

thanks

Jim
 
What Pawel said. Focal length is focal length, doesn't matter what type of lens it is. What matters is the sensor size or film format you are shooting to in relation to that focal length.

When you shoot 2K, you are shooting with a cropped region of the sensor, which means you're cutting your field of view in half compared to shooting 4K. So if you're using an 18mm lens while shooting 2K, that would have a similar field of view to shooting 4K with a 36mm lens.

As for the person you've been talking to, I'm not exactly sure why he's putting it in the context he is. It doesn't have any effect on focal lengths, DOF, etc.. It's simply a crop. If you shoot 4K with a 50mm lens and then switch to 2K with the same lens, you will need to move back much farther from your subject to keep the same framing. However, this will have an effect on perceived DOF as the size of your subject changes in relation to the size of your imaging circle on the film/sensor plane.

If you don't mind me asking, what would be your application for shooting 2K? The only real reason to shoot 2K on the RED One is for the high frame rates. Otherwise it's best to shoot one of the 4K modes whenever possible. 3K has the ability to shoot faster rates as well, just not up to the 100/120fps like 2K, but it still holds enough resolution to give a full HD transfer with sharp detail and the frame size is large enough that frame size in relation to focal length isn't as compromised as when transitioning from 4K to 2K.
 
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No problem, Jim.

I think the wikipedia article is worth a good study because it is the simplest and most accurate explanation I could find.

2k is a crop and think of it as such. So, whatever field of view you get on the image plane with S35, just crop it to half the size horizontally and vertically and you will end up with the field of view at 2k.

Therefore, you would need to use very wide angle lenses to achieve a wide angle of view and therefore the DOF won't be as shot with equivalent FOV on S35.

Hope this helps a bit. :cheers2:

Edit: hahaha, Jeff beat me to it.
 
If your DP wants a longer lens, I wouldn't let the rental house talk me into shooting 2K to fake it: the result would be roughly the same if you were to punch in (crop) in post, a tighter frame but with half the resolution. Even if your finish is HD, most people find 2K-shot material noticeably softer than 4K or even 3K.

But there are plenty of cine zooms to choose from besides the RED 18-50mm; you could always rent a nice Cooke 18-100 instead of RED's zoom, or maybe a 50-150 in addition to it.
 
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