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Filmmaking Dictionary: Number 4 / 4″ × 4″ Camera Filter
Definition
A 4″ × 4″ camera filter is a square optical filter measuring approximately four inches by four inches, or 101.6 × 101.6 mm. It is commonly used in a compatible matte-box tray or filter holder in front of the lens.
The dimensions describe the filter’s physical size. They do not identify its optical effect, density, diffusion strength or the amount of light it transmits.
Different Effects, Same Size
Filters in this size can include neutral density, optical diffusion, colour conversion, polarization and other treatments. Two pieces of glass with the same outside dimensions may therefore perform completely different jobs.
For example, a 0.6 ND reduces exposure by approximately two stops, while a diffusion filter of the same size changes aspects of contrast and highlight rendering. The size label cannot tell the camera assistant which one belongs in the tray.
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Matte-Box Compatibility
Confirm the tray dimensions and permitted filter thickness. A 4″ × 4″ filter is not the same size as a 4″ × 5.65″ filter, and the receiving tray must support the intended format. Some holders accept several sizes through specific trays or adapters.
Also check whether the filter needs rotation. A polarizer’s effect depends on its orientation, so a system that holds the glass securely but cannot rotate it may limit the intended adjustment.
Lens Coverage
A filter can fit the matte box and still vignette the image. The lens’s field of view, front diameter, filter distance and stacked trays affect whether the clear opening is large enough. Wide lenses and larger image areas deserve particular attention.
Test the widest planned lens and the full recorded area, including any open-gate mode. Corners that look clear inside a cropped monitoring guide may still be obstructed in the recorded image.
Practical Checks
- Read the effect and strength markings before loading.
- Confirm tray size, thickness and secure retention.
- Inspect for fingerprints, scratches and coating damage.
- Check vignetting and reflections with the intended lens.
- Keep filter records consistent for matching coverage.
- Store and handle optical surfaces using the appropriate protective cases and cleaning method.
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Frequently Asked Questions
Is this the same as a four-by-four diffusion frame?
No. A grip frame is typically four feet square; this filter is four inches square.
Does square glass have to be used in one orientation?
It depends on the filter. Polarizers and graduated filters require orientation control for their intended effect.
Related Terms
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