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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

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paulherrin

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There's been a lot of confusion and misunderstanding about the crop factor for the Epic/Scarlet, so here's the skinny. Explanations after Examples.

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5k
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4k
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3k
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2k
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1k
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Actually, do we need a complicated explanation? There it is, that's what you get. Choose your lenses, framerates, and compression ratios accordingly. When you shoot these resolutions, you get these crops because the sensor "windows" down and disregards the surrounding area. That's how you get your higher framerates and compression ratios. Any questions?

Good, now here's what you can do with 5k footage on the web...


UPDATE: Below is a collection of charts and resources from others. Thanks guys, useful stuff.

Jesper Sichlau:
(as compared to FF35)
Scarlet-X%2BCrop%2Bfactor%2Bsheet.jpg


Kian Marandi:
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http://www.abelcine.com/fov/


Jeff Kilgroe said:
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.
Click to expand...

Keep reading through this thread and you'll be fully equipped and ready to go. Keep shooting and make some beautiful, challenging imagery. Don't worry too much about this stuff, just be aware.

Here's a fully alternate resource with really good examples and data: http://www.reduser.net/forum/showthread.php?66210-Scarlet-X-Data-Sheet
(dragon update: [thx phil] http://www.reduser.net/forum/showthread.php?92999-Red-Dragon-Info-and-Data-Sheets)
 
NICE!
 
Thank you. This all makes a lot more sense to me now and the relative difference in terms of field of view feels a lot less severe here than I thought that it would.
 
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Thanks Paul!
 
You guys are most welcome!

I like to imagine the picture is the sensor, and each little box represents the part of the sensor being used, and thus what it sees.

Someone needs to come in with a challenge, or something... too much agreement going on so far. Or at least come in with some hard stats and mathematics, I dunno... ;)
 
Dashed lines might give the false impression that there's some kind of line-skipping involved Scott... come on! You're gonna have to step it up. :)

You gotta get mad, we're talking deep down. Somebody has a different perspective from you, so you don't like it and the best thing you can do is condescend them or otherwise virtually attack them. Funny, sad, and true. haha... i'm just as guilty as anyone else.
 
what about light sensibility when cropping? I heard that you will get more noise when you only use a part of the sensor.
 
This is why I can't use a Scarlet X : at 4K, too many data to store, at 3K it "kills" any good wide lense and 2K is not usable (just imagine the lense and stabilisation you'll need) . I need really wide shots.
 
Good example Paul :)

People should also look at the http://www.abelcine.com/fov/ - that's helpful in giving a lot of matching lens data.

Without doing any 'megamaths' (LOL) 3K seems to be similar to M4/3 - so I really think a lot depends on the prospective users own experiences with various camera systems.

Having used 35mm, 16mm, S16mm, HD (broadcast) etc - you find you adjust your point of ref accordingly :)

Now - if only the Scarlet had some Ana modes....
 
Great to have the crop factors visible there :), thanks!
I have a question. How does the fov of the scarlet's 4k compare to the red one's 4k? Am i right that red one's 4k is the same as the 5k scarlet's?
 
Imagine that I have a project set for HD delivery (1920x1080). Would the image quality "feel" any changes if I worked with different crops? I could work the "tele" shots with 3K, even 2K if faster frame rates are needed or HDRx. Then, do only the wide shots in 4K, in order to use traditional wide lenses. The data amount would be reduced considerably, but, at 1920x1080, I guess no one would suspect the difference...
 
Q: Would this crop issue be fixed if we set Scarlet to 4k and then record the signal with an external recorder at 1080? It would simply downconvert the full 4k signal to 2k for recording right? Or am I missing something?
 
Brent G Miller Jr said:
Q: Would this crop issue be fixed if we set Scarlet to 4k and then record the signal with an external recorder at 1080? It would simply downconvert the full 4k signal to 2k for recording right? Or am I missing something?
Click to expand...

That's the current theory (5K might be an issue as it won't send more than 12fps)... but 4K should be a downconvert. Epics set at 5K or 4K send the full image via HD-SDI to Pix or AJA etc, so one would presume the Scarlet will do the same :)

There are quiet a few comments on this popping up in a number of threads - so I guess we'll await clarification from RED or from the first batch of Scarlet users.

The 3K mode is interesting, as it seems (essentially) to be M4/3 - so a host of Panasonic users will be instantly used to the FOV they're getting.

Now let's hope for some Anamorphic mode additions soon :)
 
Andy White said:
That's the current theory (5K might be an issue as it won't send more than 12fps)... but 4K should be a downconvert. Epics set at 5K or 4K send the full image via HD-SDI to Pix or AJA etc, so one would presume the Scarlet will do the same :)

There are quiet a few comments on this popping up in a number of threads - so I guess we'll await clarification from RED or from the first batch of Scarlet users.

The 3K mode is interesting, as it seems (essentially) to be M4/3 - so a host of Panasonic users will be instantly used to the FOV they're getting.

Now let's hope for some Anamorphic mode additions soon :)
Click to expand...

Thank you for the info!! We're use to the M4/3 crop since we shoot on AF100 rigs but personally the 2x crop on the Panny still bugs me. Recording a 4k output to an external 2k recorder would be PERFECT. Let's hope it's possible.
 
yes, people are already using external recorders... it is and will be possible. i would be surprised if we didn't get support for anamorphic modes...
 
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