Choosing resolution and aspect ratio: Cinema
When choosing sensor size, resolution, and lenses to use for cinema, you usually choose between:
Resolution: 2K or 4K / Aspect Ratio: 1.85 or 2.39
4K Scope 2.39:1 4096 x 1716
4K Flat 1.85:1 3996 x 2160
2K Scope 2.39:1 2048 x 858
2K Flat 1.85:1 1998 x 1080
All cinemas have settings for 2K/4K flat and scope. On 2K projectors, the 4K resolution layers are discarded.
2.39 fills the screen in common-height cinemas
Most cinemas are common height, where Flat and Scope share the same height, and the screen is 2.39:1.
1.85 fills the screen in common-width cinemas
Some cinemas are common width, where Scope and Flat have the same width. And the screen is 1.85:1.
Aspect ratios smaller than close to 1.85, like 1.37 1and 2.0 are used inside Flat 1.85.
Larger aspect ratios than 2.39, like 2.66, are used inside Scope 2.39.
2.2 has been delivered in Flat 1.85, but Oppenheimer is delivered in both flat and scope. The flat version is for common-width cinemas and the scope version is for common-height cinemas. If a common-width cinema shows the scope version, the picture will be both letterboxed and pillarboxed. Read more in this post
1.85 and 2.39 have black masking around the picture in DCI/SMPTE cinemas
Both common width and common height cinemas need black masking around the image in both Flat and Scope settings to follow the DCI/SMPTE standards. Black masking around the picture increases perceived contrast.
Other aspect ratios may have black masking
Some cinemas have top/bottom and side masking for custom aspect ratios used on films like 2:1, 2.2:1, and 1.33:1.
2K or 4K
In 2023 4K DCPs are common, but some DCPs are still in 2K. But when making original content for Netflix, you must follow stricter rules, and 4K is required.
Choosing resolution and aspect ratio: Netflix
When making original 4K content for Netflix, you must use lenses that fit inside the Netflix-approved sensor size and resolution for your cine camera. The Netflix Image capture requirements have lists of approved cameras and resolutions.
Different lens sensor coverage specifications
Lens manufacturers ‘ specifications use different ways to tell which sensor area a lens will cover:
- Image circle like (Ø) 28
- Analog film formats like VistaVision
- Sensor types like Alexa LF
- The image sensor size the lens will cover in mm or inches
- Full frame
- 16/9 cropped full frame
- 4 perf super-35
- 3 perf super-35 (16/9 crop)
Examples:
- Summicron-C lenses cover super-35 and a 36 mm image circle (Ø). An image circle around (Ø) 28-32 is normal for super-35 lenses, but these lenses will also cover ARRI Alexa 35 Open Gate ( Ø 33.95).
- Atlas Orion anamorphic lenses cover a 24.89 mm x 18.66 mm sensor size
- Leitz Leica M 0.8 F.0.95 50 mm cine lens covers full frame (24 x 36)
- Cooke S4 /I cover Super 35
Some traditional analog film sizes
Source: Wikipedia
- 4 perf Academy = 21.0 by 15.2.
- 4 perf 2x anamorphic = 20.96 × 17.53 mm. Projected 2.39 anamorphic 35 mm print. Standardized in 1971
- 2 perf Techniscope = 22 x 9.47. Cropped to 2.39
- 4 perf Super 35 = 24.89 x 18.66 mm. Often cropped to 2.39 or 1.85.
- 3 perf Super 35 = 24.9 x 14 mm.
- Vistavision = 37.72 mm x 24.92 mm. Shown in 1.66, 1.85, or 2:1
- 135 film/Full frame = 36 x 24 mm
- Super-16 = 11.76 x 6.37 mm (1.85 print)
- 5 perf 65 mm = 48.56 x 22.10 mm. (Print)
- 15 perf 70 mm IMAX = 70.41 x 52.63 mm (camera)
Some modern cine-camera sensor sizes:
- 2X Anamorphic 4 perf crop of 4/3 Super 35 sensor (Alexa 35 = 20.21 x 16.95)
- 2X Anamorphic Large Format/full frame crop (Alexa LF mini = 25.97 x 21.75)
- Alexa LF Large format/full frame (36.70 x 25.54)
- 65 mm 1.85 aspect ratio (Alexa 65 = 47.32 x 25.58)
- Super 16 sensor crop (Alexa 35 = 12.44 x 6.73)
- 1.85 Super-35 4K sensor crop (Alexa 35 = 24.27 x 13.12)
- 2.39 Super-35 4K sensor crop (Alexa 35 = 24.88 x 10.42)
- Alexa 35 Open Gate (27.99 x 19.22)
Choosing sensor size and lenses with the Arri framing lens and illumination guide
If you record in 4.6 Open Gate ArriRaw mode on the Alexa 35, using the Arri framing lens and illumination guide is important. This mode lets you capture the entire sensor area and use framing lines to mark different aspect ratios, such as 2.0, 2.39, or 1.85. However, the open gate sensor size is slightly larger than Super-35, so some Super-35 lenses may not cover it completely. You can use the Arri framing lens and illumination guide to check the lens coverage. This tool shows how much each lens covers the framing line at different focus distances and apertures. For instance, you can see if a lens covers the 2.39 framing line without vignetting at close focus and wide-open aperture. (e.g. f/2), or at infinity focus and closed-down aperture (e.g., f/4). If a lens does not cover the desired aspect ratio, you can make a custom framing line scaled down to fit the lens. You can also scale down the framing line to leave extra space around the image for post-production purposes, such as stabilization, barrel distortion effect, or re-framing.
Some aspect ratio, camera, and lens examples from the ARRI guide
2X Anamorphic Large format crop in 4K Scope Netflix/Cinema (ARRI Alexa LF Mini)
The ARRI Alexa LF and LF mini are allowed by Netflix to shoot with 2X anamorphic lenses in a 3148 x 2636 crop of the 4.5 K LF Open Gate sensor.
When making a custom framing line in the Arri framing lens and illumination guide for 3148×2636, the sensor size used is 25.97 x 21.75 mm. This is larger than the normal 4-perf anamorphic sensor size (20.96 × 17.53 mm).
The Netflix guide states that ARRI Master anamorphic lenses from 40 mm cover this area, but some anamorphic lenses need an LF extender because of the large sensor size. You can check this in the Lens Illumination Guide.
Using a 40 mm Master Anamorphic clears the 3148 x 2636 framing line
The Arri Rental Alfa lenses are detuned, and modified versions were made for ARRI Alexa LF and used on the film The Batman (prototype) and the Netflix tv-series 1899.
Using Cooke S4 and Leitz Summicron-C lenses on Open Gate ARRI Alexa 35 with framing lines for 2.39 (cinema/Netflix)
The ARRI Alexa 35 4.6K Open Gate specification:
Resolution:
4608 x 3164
Sensor Size:
27.99 x 19.22
Image Circle
33.95 mm
The Leitz Summicron-c lenses cover a 36 mm image circle and 2.39 (4608 x 1930/ Ø 30.34). And the open gate sensor (4608 x 3164/ Ø 33.95) area.
Other lenses, like the Cooke S4/I 16 mm, cover the aspect ratio of 2.39 with some vignetting at aperture 2. You can scale down the framing line to avoid vignetting or decide to keep the vignetting.
LF/Full frame Open Gate with framing line for 1.85 Cinema (ARRI Alexa LF Mini)
LF open gate sensor on the ARRI Alexa LF Mini is a bit larger than the 36 x 24 full-frame sensor size:
Sensor Size:
36.70 x 25.54 mm
Resolution:
4448 x 3096
Image circle:
44.71 mm
Lenses like the Leitz Cine Leica M 0.8 50 mm F 0.95 will cover 36 x 24. but the Leitz lens specifications warn that there can be some shading/vignetting on the Arri LF mini open gate mode (36.70 x 25.54)
There is some vignetting outside the 1.85 framing line in open gate mode at F 0.95 on the 50 mm lens. But when stopped down, this will be reduced, and at F 4, there is no vignetting. Custom framing lines can be made if there is too much vignetting.
At F 4, there is no vignetting.
2X Anamorphic crop of 4/3 Super 35 sensor in 4K Scope Cinema (ARRI Alexa 35)
The ARRI Alexa 35 has a Super 35 4/3 sensor with 4.6K resolution.
With the ARRI Alexa 35, you can directly record 4K DCI resolution in C-LOG4 ProRes 4444 4K 2.39:1 Anamorphic 2x 3328×2790 (20.21 x 16.95 mm) desqueezed and scaled to Scope 4K DCI 2.39 (4096×1716).
Using the Arri framing lens and illumination guide, you can choose the Prores 4K anamorphic mode.
Because the sensor area is 20.21 x 16.95 mm, you can use traditional 4 perf anamorphic lenses like the Atlas Orion lenses without an LF extender.
2X Anamorphic 4 perf crop of 4/3 Super 35 sensor in 2K Scope Cinema (ARRI Alexa Mini)
The discontinued ARRI Alexa Mini has a 3.4K sensor. The 4K anamorphic sensor size on the ARRI 35 is similar to the 2K anamorphic mode on the Alexa Mini, which has a 21.12 x 17.70 mm sensor size when recording 2K Scope 2560×2145 desqueezed and scaled to Prores 2K DCI 2.39 2058×858.
1.85 Super-16 sensor crop in 2K Flat (ARRI Alexa 35)
Because the ARRI Alexa 35 has 4.6K resolution, you can use it with super 16 lenses in s16 16/9 mode (2048×1152) and use a 1.85 framing line (2048×1108)
Sensor size is 12.44 x 6.73 /Ø 14.27 mm. It can be downscaled to 2K Flat 1.85:1 1998 x 1080 for 2K DCP delivery.
1.85 Super-35 sensor in 4K Flat Cinema (ARRI Alexa 35)
Example: ARRI 35 with Cooke S4/i 25mm. In 4K DCI 16/9 4096×2304 recording mode with custom 4K DCI Flat 1.85 (3996×2160) framing line.
24.27 x 13.12 sensor size / Ø 27.59
2.39 Super-35 sensor in 4K Scope (ARRI Alexa 35)
Example: ARRI 35 with Leitz Summicron-C 35 mm in 4K DCI 16/9 4096×2304 recording mode with DCI 4K Scope (4096×1716) framing lines.
24.88 x 10.42 sensor size / Ø 26.97 mm
65 mm sensor size Framing lines for 1.85 (ARRI Alexa 65)
ARRI Alexa 65 can record in 65 mm Open Gate mode
Specifications:
6560 x 3100 Open gate
With framing line for 1.85:1
Resolution:
5736 x 3100 px
Sensor Size
47.32 x 25.58 mm
Image Circle:
53.79 mm
