my guess will be filters smaller than 77mm
maybe 67mm? all plastic construction
I doubt it'll be an all plastic construction simply because of its L designation.
Most L series lenses share a number of common characteristics:
- Tough build, made to withstand trials in the field (some incorporating dust and moisture resistant rubber seals).
- At least one fluorite or ultra-low dispersion glass element, combined with super-low dispersion glass and ground aspherical elements.
- Non-rotating front elements, which are optimal for some filters (e.g. circular polarizers).
- Relatively large apertures compared to other Canon lenses in the same focal lengths.
- Ring-type USM (ultrasonic motor) and full-time manual focusing.