What is a lens hood and why do I need one?
A lens hood is a device that is attached to the front of the lens in order to shade the front element. This is done to reduce stray light which can cause glare, reduce contrast or introduce unwanted artifacts into the image. Shading is especially important for older single-coated or uncoated lenses. A properly shaded lens can produce visibly richer colours and higher contrast. Lens hoods are also useful for mechanical protection of the front element in use and transit. They can prevent damage from bumps, scratches, rain (within reason) or the occasional stray finger.
What are the different types and how do they work?
Bayonet-mount lens hoods
The most common type of lens hood is the plastic bayonet-mount cylinder that screws to the front end of the lens housing. These come bundled with most high-end lenses and are usually offered as accessories for cheaper lenses. Because the shading requirements of each lens are different, typically this type of lens hoods are not interchangeable between different lens models.
The advantage of this design is that it offers maximum physical protection and tailored shading for each individual lens. They usually attach to the outer barrel of the lens via a twisting bayonet mount or locked in place with spring loaded pins. This type of lens hood allows undisturbed use of screw-in filters. With wide angle lenses that use shallower lens hoods you don’t even need to remove the lens hood to put on, adjust or remove a filter. The only drawback of this setup is the need for a separate lens hood for each lens, which can add (albeit minimally) to the bulk and weight of gear.
This is partially remedied by the design of most lens hoods, which allows them to be mounted backwards on the lens. This reduces the length and only impacts the circumference footprint of the lens in your bag. It also might provide a bit of mechanical protection to focus and/or zoom rings in the process.
Screw-in lens hoods
The second type of lens hoods is the screw-in type, which screws in the filter threads on the front of the lens. This type of lens hood can be seen more often on vintage lenses and particularly on rangefinders. Screw-in lens hoods are also the second best option for lenses that were not designed with a dedicated lens hood by the manufacturer. Nowadays, screw-in lens hoods are more often encountered as third-party accessories. Virtually all manufacturers of photographic camera optics offer dedicated bayonet mount lens hoods for their current lenses.
The screw-in design means that one lens hood can be physically screwed on different lenses with the same thread diameter or through step down rings. However, the fixed length means that it can provide optimal shading for only one designated focal length or lens model. Another drawback of the screw-in lens hood is that it is more cumbersome to attach or remove from the lens. Frequent attachment and removal also increases wear on the lens’ filter threads and runs the risk of cross-threading. If you decide to keep the shade on the lens it might require a different size cap, if it supports one at all. Screw-in shades also complicate the use of screw-in filters. They cannot be reverse-mounted on the lens like bayonet lens hoods which makes storing and transporting them a bit more troublesome. Screw-in lens hoods are usually made of metal, but there are rubber variations that are a bit more flexible.
Screw-in rubber lens hoods are a bit more universal solution, as their construction usually allows for several positions resulting in different effective lengths of the hood.
Compendium lens hoods
Finally, at the more sophisticated end of the lens shading spectre we have the various iterations of the compendium lens shade. They come in many shapes and sizes, and every large format system manufacturer offers (or has offered at some point) a variation of a compendium shade. Due to the specifics of large format photography, a fixed lens shade is of little use once focal plane manipulation is employed.
Compendium shades are generally built with sufficient adjustability to offer optimum shading in a variety of camera setups. This adjustability also means that unlike the dedicated shades of 35mm and medium format lenses, a single compendium shade can successfully be used on a wide variety of lenses. In addition, many compendium hoods offer square or rectangular unmounted filter holders, much like their motion picture equivalents. Naturally, this flexibility comes at a higher price, in addition to the cost of increased complexity and longer set-up time.