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Scarlet-X Sensor Crop Calculation Chart

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Kian Marandi

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Hi All,

Out of my own curiosity I did some basic calculations to determine the effective sensor size for Scarlet-X when shooting in the reduced-res modes.

Assumptions:

- Resolutions at different shooting modes taken from RED published data (that chart that's been floating around with the redcode numbers)
- Sensor Dimensions in 5K = 27.7mm x 14.6mm (this is taken from the Lens Coverage numbers on the Scarlet product page on red.com. I interpreted this as what the sensor actually "sees" coming from the lens. Thus, the effective sensor size at 5k).
- Calculated a base pixel density for the horizontal and vertical dimensions, and used that throughout to determine crop dimensions.

Note: I didn't include diagonal calculations for pixel density and pixel count, because I think it can be misleading. Not sure how, but just a feeling. Just included diagonal dimensions.

If my base numbers (e.g. full 5k sensor dimensions) are incorrect, please tell me ASAP and I'll change it to make sure this isn't misleading.

Hope it's useful.

Thanks,
Kian

P.s. I`ve never attached anything, so I don`t know if it worked.
 

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can a red moderator confirm this is accurate? Ive been searching for this info as well!
 
Charles Wood said:
can a red moderator confirm this is accurate? Ive been searching for this info as well!
Click to expand...

I 2nd that. And can we get a Crop Factor out of this? in 35mm eq.? Like the Canon 550d has a 1.6 Crop?
To just get a feel for what we get?

George
 
I also made one:

Scarlet-X%2BCrop%2Bfactor%2Bsheet.jpg
 
So if I get this right, shooting Scarlet-X in 24fps cinema motion at 4K or Quad HD gives us a factor of 1.6 X the MM on our lens, right?
This would make:
the Cannon 16-35 f2.8L a 25-56 mm lens,
the Cannon 24-70 f2.8L a 39-112mm lens.
the Cannon 200mm 2.8 fixed is now a 320mm lens.
(in comparison to a 35mm film STILL camera, where 50mm is human eye.)

Or am I completely stunk and droned?
 
Thanks, Kian, George, and Jesper for all this info. This will GREATLY help people select lenses.

My guess, anything over about 70mm we would want "IS" or image stabilization, as we are effectively over 110mm telephoto range (on a 35mm film still camera).
 
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emil tanem said:
What would be good options for covering the wider end on PL mount then? The Red lenses on ly goes to 17-18mm which is ~28mm. I would like to have a wider option. SOmthing equivalent to 18mm in FF.
Click to expand...

Emil, a lot of people looking for a wider PL mount lens use the Duclos 11-16mm T2.8. They are originally the highly acclaimed Tokina 11-16mm for Canon/Nikon mounts and are converted to PL by Duclos. Effectively at 4k this will give you an 18-26mm, 3k would be 22-32mm and 2k would be 43-62mm.

http://www.ducloslenses.com/Duclos_Lenses/PL116.html
 
Pity that the Duclos 11-16 is on backorder (5 months or something like that)

so if I understand this right, shooting in 4k with the new Zeiss ZE/F 25mm f2.0 would give me a 40mm lens on a 35mm FF camera?

@ Carter, so the RPP 18mm on the RED (5k or 4k) is not really that wide as compared to using a Zeiss 18mm f3.5 on a full frame stills camera like (5d, d3)? RPP 18mm in 5k = 23,4 and in 4k like you wrote, 28mm

I've read some comments how directors like Polanski, Kubrick, Welles liked using the 18mm, but really they were using (in FF35 terms)
more or less a 28mm?
 
Last edited:
Hello,
I was wondering about that crop factor issue at 2K. Its no really nice to have a 2/3 sensor like when you work at 2k so I was looking for a solution:
1. is it possible to work at 4K and have the lowest like 12:1 or 11:1 or 10:1 and therefore match the file size and quality of full HD ?
2. The SDI or HDMI output is in Full HD and if the scarlet is set at 4K would it be a solution to use an external recorder such as an Atomos Ninja and still use the sensor like an aps-c

I don't know if I'm clear but I would be able to shoot at a Full HD like quality and file size and have the crop factor of an APS-c and not 2/3.
 
According to Jesper's Crop Factor chart above, at 5k, the sensor crop factor is 1.3.
Your 18mm lens X 1.3 -24mm (when compared to a 34mm film still camera). Your 25 would be about 32.

As you reduce capture resolution, the sensor windows down, and the crop factor increases. So does DOF.
So at 4K Cinema Motion, the factor is now 1.6. You are using less of the sensor. The 18mm is now a 29mm.
At 3k, the factor is 2.0. The 18mm lens is about a 36.

When you reduce "K" of capture resolution, you simply use less of the sensor, the very center portion.
At 2k, you are using less than 1/4 of the sensor area. You capture less info and have MUCH smaller RAW files.
Your lenses get "longer". You get more Depth of Field.

2K is actually larger than "FULL HD" and still RAW . . . until you send it to an external recorder that compresses it.
 
Thank you but that was not my question. I was probably not clear.
I totally understand crop factor DOF and lenses issues. My question was to find a solution to not have to crop the sensor and still be able to not have such heavy files .

What i'm not sure is when the red is set to 4K and you use an external monitor with the sdi or HDMI output which are in 1920 x 1080p, the image coming out is not "croped" (I think) therefore one could use an external recorder and have a 1920 x 1080p image with a 1.6 factor?
If that is the case and if some one knows what goes on when you shoot in 4K and out put in 1920 x 1080p, i'll be happy to know.

Another thing to avoid having very large files and hundreds of ssd and still use the 1.6 crop factor:
Is it possible to shoot in 4K with a low "compression" which would be about the same compression quality and file size of the 2K ?

Thanks
 
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