Open Gate Demystified: How to Frame and Crop Better

What is Open Gate?

In film cameras, the “gate” is the metal window that shapes how much of the film stock gets exposed. Shooting “open gate” meant using the full window, with no crop mask in place.

Digital cameras borrow the term: open gate records the entire sensor instead of a preset crop like 16:9 or 2.39. You capture extra height and width together.

That extra space helps with reframing, stabilizing, and multi-format delivery. It also keeps options open when a client changes the aspect late in the edit.

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Open Gate on the Arri Alexa 35 Xtreme

The ARRI Alexa 35 Xtreme is classified as a Super 35-sized sensor:

This is the entire sensor you can record in. In other words, the Open Gate.

The resolution is 4608 x 3164, which is the maximum possible resolution possible with the Alexa 35 Xtreme. The aspect ratio is about 1.45:1.

Now let’s say you want to frame a scene for 2.39:1, 16:9 and 4:3, this is what it will look like:

And, if you want to shoot in 2x anamorphic, you’d need an aspect ratio of 1.2:1, which would look like this:

By recording Open Gate, you keep all the information outside the crop you want, but you have the freedom to:

• Reframe the image slightly if you want to (like if a boom slipped into the shot).
• Release the film in different aspect ratios if you want to.
• Maybe release the “Open Gate” version in the future as a bonus or special edition.
• Use the extra area for stabilizing the footage in post, without having to crop the image and lose resolution, or
• Just leave it as is, and crop where you originally intended.
• In some cameras, you don’t get extra headroom outside the Open Gate mode, so this mode allows you to correct for actor movement quicker because you can see outside the frame.
• If you’re using vintage lenses that vignette badly in the corners, or have poor edge characteristics, this is a good way to get them trimmed. However, if the lens is designed for a specific format it might not help that much.

Cameras like the Arri Alexa LF have a full frame sensor (Arri calls it Large Format). This bigger sensor area allows you even more freedom, because you can crop to pretty much all of the traditional film and cinema formats.

The best thing is, full frame LF gives you a bit more freedom to crop for vertical content:

In Open Gate the color science and highlight rolloff and so on do not change, for any camera. You are only changing how much of the sensor you read.

Why don’t cameras only have Open Gate?

Cameras like the Alexa 35 Xtreme and LF allow you to film in many modes, and the reasons for it are as follows:

• Data rate: Open gate has the highest data rate in Arriraw, being the highest resolution. Sometimes you just don’t want to deal with all the data.
• Frame rate: Some cameras allow you to film in faster fps when the sensor is cropped, since it increases readout. Red cameras are famous for this.
• Maybe you’re not allowed to or don’t want to film in RAW, and you’re forced to use one of the alternative options.

Open Gate Sizes on Cine Cameras

Here’s a quick-reference table for each camera’s Open Gate mode.

How Open Gate Changes Framing and Crop Decisions

Framing with Open Gate starts with intent. Pick the hero aspect ratio first. If you don’t know about cinema formats, check this primer out:

Then protect a safe area for likely alternates. Use frame lines on set to keep eyes, logos, and ceilings inside both boxes. All good cinema cameras allow for frame lines. If not, an external monitor will surely have it.

Pick the format that matches your lenses, your subject distance, and the release plan.

Do not assume all lenses cover Open Gate. Stills full frame lenses might cover 3:2 full frame, though that’s not always the case. Some cinema lenses mark coverage for Open Gate or show where falloff begins.

Test at your widest focal length and closest focus, since corners get darker there. Telephoto lenses tend to have a greater image circle coverage. Test everything!

Use frame lines and desqueeze settings that match your plan. Add a small center-cut box on the monitor so you can place faces and titles with confidence.

You need to do all this prior to setting foot on a film set!

In post, watch debayer and scaling order in the pipeline. Some NLEs scale before a proper debayer if the setting is wrong. That can soften the image. Make sure your project resolution is equal to open gate in editing. Export from the native resolution first, then scale to deliverables from the master.

The master should always be open gate, unless you really don’t want the extra bits.

I would also keep the proxies in the full open gate resolution.

If you plan VFX, lock the target aspect ratio early so the vendor does not have to rebuild edges. Add extra handle pixels on all sides so VFX has room for tracks, patches, and glows.

How to Decide between Full Frame and Super 35 Open Gate

Pick full frame Open Gate if you want the shallowest depth of field at a given angle of view, or if you want a full frame anamorphic film.

Full frame also gives you the most crop room for stabilization and multi-format masters.

Pick Super 35 Open Gate if you already own S35 cine glass, if you need longer apparent reach, or if you prefer deeper focus at the same stop.

Your story, lens kit, and release map should drive the choice.

Open Gate is simple in idea and powerful in practice.

Capture more sensor. Frame with intent. Protect for the formats you actually need.

All modern cinema cameras offer strong Open Gate options (or at least full frame options larger than traditional cinema formats) in full frame and Vista Vision classes.

Use the extra area to serve the cut, not to fix avoidable mistakes. Do that and you will frame and crop better without drama.

Hope this helps!