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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 :)

Crop Factor Demystified

Michael Ayers said:
Then what I really need is a way to record the 4k data externally. It is a long story that I won't bore anyone with now, but I MUST record all of my data on an external high-performance DVR. Is there any way to do that and still get the 4K/redcode (some extra module, for example)?

If it is indeed true that the hd-sdi data are scaled to 1080 from the full sensor, then I would probably be happy with that, but I would need some official word from RED, or actual users, before deciding to go that route (I know, that answer will come in a few weeks, which is fine. Whenever someone knows that for sure please post a thread about it!)
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better give us the long story... in a concise manner if possible. when you think you must do anything, outside insight is usually the only must.
 
paulherrin said:
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Jeremiah Kuehne said:
That's awesome and helpful! Now can someone explain to me how the crop factor affects the lens?
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Crop factors don't affect lenses. Lenses don't have crop factors, imagers (sensors, film) do.

When you crop down to a lower resolution on the RED One, EPIC or SCARLET, you are recording a smaller area of the sensor. If we look at the crop diagram posted by paulherrin, you can see what's happening. He didn't specify what focal length and what camera (imager size) this space shuttle shot was taken with. Doesn't really matter, it's for illustrative purposes. But let's assume that it's taken with an EPIC or SCARLET and is 5K (5120 pixels) wide. Since all the cameras RED currently offers use the same sensor, we can quickly determine recordable area size by multiplying the recorded resolution by the size of photosites (sensor pixels), which happens to be 5.4 microns or 0.0054mm.

5120px * 0.0054mm = 27.648mm imager width.

Let's say this shot was taken with a 50mm focal length (hehe, yeah, right..)... We would know that a crop to 4K from 5K would be 1.25. So if we crop to 4K and want the same relative framing or Angle of View (AOV), we could take 50mm / 1.25 and see that we would want a 40mm focal length. It's also easy to see that 2K is half of 4K, so if you want the same relative framing when you crop to 2K, then you would need a 20mm focal length.

You can always relate crop factors back to FF35, as many DSLR shooters feel required to do for some strange reason, just by knowing that imager size is 36mm. So 36 / 26.748 = 1.3. Meaning that 5K is a 1.3X crop from FF35. So if you have a 100mm focal length on FF35, the equivalent on RED 5K would be 76.9mm, or just call it a 75mm since you can actually buy those, or set your zoom at a fuzz over 76...

Personally I don't relate to FF35... I'm more of a medium format guy, but I tend to just get into a habit of knowing how focal lengths relate to the different camera imager sizes I shoot with. If I need to whip out a calculator to punch in some numbers, I rarely do a crop factor like above, I'm more likely to figure out what I want framed in the shot and how wide that field of view is and at what distance, then I can determine exactly what AOV I should be looking for and I typically know which focal length produces that AOV on my camera(s).

When you get away from FF35 circles, and start talking crop factors. Many people will ask you "in relation to what?". Not everyone thinks in FF35 terms.
 
paulherrin said:
It only affects which lens you choose to shoot a particular shot with.
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So...the larger the crop factor, the more of a "zoom" that there is? Tell me if I'm wrong, but wouldn't it mean that a 15mm lens or so wouldn't seem Ultra Wide, it would seem more like tele? I think I understand..
 
Hey Paul,
Nice. To make it more moron proof, any chance you can put lens MM on each of the "K" windows using the 5K as relative reference? IE: To match FOV of 50mm at 5K you need a 12mm at 1K

That would be cool for those changing frame rates on a Scarlet but need to match frame crop of normal speed (maybe a prior take). That make sense?
 
Yes, as you crop in, you are using a smaller area of the sensor. Therefore, you need a shorter focal length (wider lens) to maintain the same relative framing that you had when using a larger area of the sensor. Hence my example above, if you shoot 5K with a 50mm lens, then at 4K you would want a 40mm lens to keep the same framing. At 2K, you would want a 20mm lens for the same framing... a 10mm lens at 1K or a 30mm lens at 3K. In case you didn't notice, I picked 50mm as a reference point since it keeps all the numbers nice and neat.

I'm not sure I'd want this to be any more "moron proof". No disrespect meant to anyone, but this is basic photography 101 stuff here. Focal lengths, framing (AOV/FOV) and cropping are like the first thing people need to understand in order to call themselves a photographer, cinematographer, or god help us, a DoP. Then again, maybe I'm barking up the wrong tree with that... Everyone owns a camera these days.
 
Thank you so much Jeff! I don't mean to take up all your time, but I'm just a 16 year old kid trying to pick up absolutely every bit of information that I can about cinematography..anyway, would you be so kind as to explain how to determine AOV? Like, could you describe how you would calculate a proper shot? I know there are formulas..I'm not very familiar with them, but I know they exist.
 
Jeff Kilgroe said:
Yes, as you crop in, you are using a smaller area of the sensor. Therefore, you need a shorter focal length (wider lens) to maintain the same relative framing that you had when using a larger area of the sensor. Hence my example above, if you shoot 5K with a 50mm lens, then at 4K you would want a 40mm lens to keep the same framing. At 2K, you would want a 20mm lens for the same framing... a 10mm lens at 1K or a 30mm lens at 3K. In case you didn't notice, I picked 50mm as a reference point since it keeps all the numbers nice and neat.
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R YOU PSYCHIC? see my prior post
 
Josh Beadle said:
R YOU PSYCHIC? see my prior post
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Lol. Honestly after that incredibly easy to understand explanation, I do feel like an idiot. If I were to go to film school, would there be a lesson taught on this, or would it already be assumed I know this stuff?
 
Jeremiah Kuehne said:
So...the larger the crop factor, the more of a "zoom" that there is? Tell me if I'm wrong, but wouldn't it mean that a 15mm lens or so wouldn't seem Ultra Wide, it would seem more like tele? I think I understand..
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I think you're getting the idea. It doesn't take that long to get used to once you start shooting with the camera. When you switch between modes, the image shows just like the series of pictures in my first post. In a sense, it is kind of like zooming or punching in, though the generally accepted terminology is cropping or windowing.
 
paulherrin said:
I think you're getting the idea. It doesn't take that long to get used to once you start shooting with the camera. When you switch between modes, the image shows just like the series of pictures in my first post. In a sense, it is kind of like zooming or punching in, though the generally accepted terminology is cropping or windowing.
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I understand. I think a lot of my questions would clear up if I had a solid week to work with the camera..best I can do for now is read and learn. :/
 
Jeremiah Kuehne said:
. . . If I were to go to film school, would there be a lesson taught on this, or would it already be assumed I know this stuff?
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No, there would be a full year on this topic alone - which you can take out a school loan to pay for ; )
 
Jeremiah Kuehne said:
Thank you so much Jeff! I don't mean to take up all your time, but I'm just a 16 year old kid trying to pick up absolutely every bit of information that I can about cinematography..anyway, would you be so kind as to explain how to determine AOV? Like, could you describe how you would calculate a proper shot? I know there are formulas..I'm not very familiar with them, but I know they exist.
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i've learned almost everything i know from this forum. which has lead me to worry a lot less about technical data and calculations. just get out there and shoot with whatever resources you have. good films don't come by means of scientific method.
 
paulherrin said:
i've learned almost everything i know from this forum. which has lead me to worry a lot less about technical data and calculations. just get out there and shoot with whatever resources you have. good films don't come by means of scientific method.
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So I'm guessing this means you aren't an advocate of film school? Personally, I think that forums like these are better sources of information than film school would be, but I don't want to be seen as speaking out of ignorance. I think Camera + reduser > film school. :)
 
Jeremiah Kuehne said:
So I'm guessing this means you aren't an advocate of film school? Personally, I think that forums like these are better sources of information than film school would be, but I don't want to be seen as speaking out of ignorance. I think Camera + reduser > film school. :)
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i am an advocate of personal growth and learning. progression can be nurtured in many ways. usually this involves some kind of structure, even if it is in the guise of non-structure. film schools have helped a whole lot of people realize and develop their potential, perhaps at a higher success rate than those who opted for a different path. collaboration and openness to ideas that challenge your own are key factors, which a school setting can sometimes set up quite easily. i believe this forum sets that up very well, too.

nobody gets better because they went through a certain program or bought a certain camera or sat on a certain forum. you get better because you decide to get better, and listen to disagreement patiently to understand "new" ideas.
 
lens performance

lens performance

What is your experience with lens performance when cropping the sensor? How do these lower end digital lenses look when you crop-in the picture?

Also, has anyone seen footage yet? I'd like to see some 4k, 3k, 2k and 1k examples.
 
footage would be interesting, I mean a comparison shot with different modes using the same lens.

The crop factor is demystified easily, but the end result is not, at least not for me. Less lens resolution, 4 times more noise compared to 4k scaled down, maybe more shake when doing handheld shots. With such a comparison these fears could be demystified as well. Or confirmed.
 
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