Choosing sensor size, resolution, and lenses on cine cameras

Resolution and Aspect Ratio in Digital Cinema

1. Standard DCP Resolutions and Aspect Ratios

DCI (Digital Cinema Initiatives) specifies four standard resolutions:

Note: All cinemas can handle both 2K and 4K in Flat and Scope formats. 2K projectors automatically discard the 4K resolution layer.

2. Cinema Screen Configurations

a) Fixed-Height (Common Height) Cinemas:

• Most new cinemas use this configuration
• Screen aspect ratio: 2.39:1
• Scope (2.39:1) fills the entire screen
• Flat (1.85:1) is centered with pillarboxing

b) Fixed-Width (Common Width) Cinemas:

• Screen aspect ratio: 1.85:1
• Flat (1.85:1) fills the entire screen
• Scope (2.39:1) is centered with letterboxing

3. Handling Other Aspect Ratios

a) Aspect ratios smaller than 1.85:1 (e.g., 1.37:1, 2.0:1):

• Typically delivered within a 1.85:1 (Flat) container

b) Aspect ratios between 1.85:1 and 2.39:1 (e.g., 2.0:1):

• Usually delivered in 1.85:1 (Flat) container
• Exception: “Oppenheimer” (2023) was delivered in both Flat 2.2:1 and Scope 2.2:1 versions. read more in this post

c) Aspect ratios larger than 2.39:1 (e.g., 2.66:1):

• Delivered within a 2.39:1 (Scope) container

4. Black Masking

• DCI/SMPTE standards require black masking around the image for both Flat and Scope formats in all cinema types
• Black masking enhances perceived contrast
• Some cinemas have adjustable masking for custom aspect ratios (e.g., 2:1, 2.2:1, 1.33:1)

5. 2K vs. 4K

• As of 2024, 4K DCPs are common, but 2K DCPs are still in use
• For Netflix original content, 4K is mandatory

Understanding these standards and variations is crucial for filmmakers and cinematographers to ensure their work is presented as intended across different cinema configurations.

Choosing resolution and aspect ratio: Netflix

To create 4K content for Netflix, it is essential to use lenses that are compatible with the approved sensor size and resolution specified by Netflix for your cine camera. Netflix provides a set of guidelines for image capture, including a list of approved cameras and resolutions, along with a calculator to ensure compliance with the allowed sensor size. The Netflix Image capture requirements

Choosing sensor size and lenses

Lenses and cine-cameras for films are frequently selected based on their ability to impart a distinctive visual style. Here are a few common examples of such style choices:

• Anamorphic lenses like Atlas Orion or spherical lenses like the Leica Summilux
• Modern lenses like the Arri Signature Primes or vintage lenses like the Canon K35

Factors such as budget limitations, Netflix specifications, and equipment availability should also be taken into consideration. For further information on selecting lenses and cine-cameras for a cinema film, refer to this post .

Using the Arri framing lens and illumination guide

When shooting a film in wider aspect ratios like 2:1, 2.2:1, or 2.39:1 for cinema or Netflix, you have the option of using either anamorphic or spherical lenses. However, it’s crucial to ensure that your chosen lenses can adequately cover the sensor size of the camera you’re using. The Arri framing lens and illumination guide is an invaluable tool for this purpose.

For instance, if you’re planning to shoot in 2.39 aspect ratio using spherical lenses in 4.6 Open Gate ArriRaw mode on the Alexa 35 camera, it’s important to note that the Open Gate sensor size is slightly larger than Super-35. As a result, some Super-35 lenses may not fully cover the sensor.

This is where the Arri framing lens and illumination guide comes in handy. It allows you to check the lens coverage, showing how much of the framing line each lens covers at various focus distances and apertures.

In cases where a lens doesn’t cover the desired aspect ratio, you have options. You can create a custom framing line that’s scaled down to fit the lens coverage. Additionally, you might choose to scale down the framing line to provide extra space around the image for post-production needs, such as stabilisation, applying a barrel distortion effect, VFX work, or re-framing.

Example: Using 2X anamorphic on a Netflix film with the Arri Alexa 35

Link:The Arri Alexa 35 guide for Netflix films

If Netflix approves the use of 2.39 aspect ratio on a film, according to the Netflix calculator, it is permissible to use a 2x anamorphic lens on a film with a 2.39 (or 2.2) aspect ratio. This can be achieved with the Arri Alexa 35 camera in 4.6 3:2 open gate mode, along with a e.g.10 percent safety crop. The camera and sensor mode should be set to Arri Alexa 35 – 4.6K Open Gate. The lens squeeze factor should be set to 2X. The desired output aspect ratio is 2.39:1, with a 10 percent safety crop.

Camera and Sensor Mode
Arri Alexa 35 – 4.6K Open Gate
Lens Squeeze factor
2X
Output Aspect Ratio:
2.39:1
Safety Crop
10 percent

Results:
Framing Resolution
Sensor Resolution
4608×3164
Active Image Resolution
3400×2848
Maximum allowed sensor crop
3148×2638

Working Resolution
Sensor Aspect Ratio (squeezed): 1.46:1
Content Aspect Ratio (desqueezed): 2:91:1
IMF active image resolution: 3840×1610
Working Resolution (Proposed): 5208×1788
Working Resolution (Minimum) 4268 x 1788

The active Image resolution is 3400×2848 and above the maximum allowed sensor crop 3148×2638. You can then check if your lens covers the sensor area in the Arri framing lens and illumination guide

With the guide you can check if the lenses that are going to be used fit inside the approved sensor size if you are using a large 10 percent safety crop. The Arri Master Anamorphic 28 mm (aperture 1.9) fits.Others lenses that covers 20.64 mm x 17.30 mm or 26.93 mm image circle should also fit.

When removing the safety crop it will also fit

Example: ARRI Alexa LF Mini framing line for 1.85 Cinema

The ARRI Alexa LF Mini features an Open Gate sensor that’s slightly larger than the standard 36 x 24mm full-frame sensor:

Technical Specifications:

• Sensor Dimensions: 36.70 x 25.54 mm
• Resolution: 4448 x 3096 pixels
• Image Circle: 44.71 mm

When using lenses like the Leitz Cine Leica M 0.8 50mm F/0.95, which are designed for 36 x 24mm coverage, some considerations should be noted. Leitz specifically cautions about potential shading/vignetting when using these lenses in the Alexa LF Mini’s Open Gate mode due to the sensor’s larger dimensions.

We observe significant vignetting beyond the 1.85:1 framing line when shooting wide open at F/0.95 with the 50mm lens. However, this effect diminishes as you stop down the aperture, completely disappearing by F/4.

We see vignetting at F.0.95

At F 4, there is no vignetting.

For additional flexibility in post-production, you can downscale to DCI 4K Flat (3996 x 2160). This provides extra room for VFX work or reframing while maintaining professional resolution standards.”