DaveD65 Loc: Queen City, Ohio

I've searched through this forum to find the answer to my question with no luck finding it. Why do video cameras use a square or rectangular lens hood, when we mostly still photographers us a round one? And why do the round shades usually use a (tulip shape)? Way back we only used round (no petal shapes)?

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Petals transform round to square to match the format. But round is still better than nothing. OTOH we (I) were already using square hoods way back when (and still do).

Longshadow Loc: Audubon, PA, United States

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Adjustable video hoods are very effective, but most non-studio stills users dont want to deal with all that bulk. More or less an on-tripod vs off-tripod situational preference.

R.G. Loc: Scotland

To do an optimum job of keeping unwanted light away from the lens opening, the hood needs to stay just out of sight (i.e. not appearing on the sensor). Geometry and optics dictate the shape of the "petals". In the case of a zoom lens it's the widest zoom (the shortest focal length) that dictates the shape of the hood.

Longshadow Loc: Audubon, PA, United States

Because the shortest focal length has the widest field of view.

R.G. Loc: Scotland

Exactly.

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UHH Advice and Wisdom regulations caution that the simplest answer is always the worst. Lets see what the next ten pages bring ...

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What goes around comes around.

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Mac Loc: Pittsburgh, Philadelphia now Hernando Co. Fl.

Most (not all) of my Leica lenses have rectangular lens hoods. The Leica lenses that I have with round lens hoods are lenses that have retractable, built in lens hoods.
The tulip lens hoods are for wide angle lenses, as the focal lengths be come longer the hoods tend toward round.

DirtFarmer Loc: Escaped from the NYC area, back to MA

In the old days (1950s) I didn't even have lens hoods.

When I started with DSLRs they all had petal hoods. But I only had zoom lenses. Eventually I got a 50mm and it had a round hood. Later on I got a 200-500 and it also had a round hood. The most extreme petal hood is on my 28-300.

The petal hoods are designed so that the hood will be out of the field of view, but if that were strictly true, the notches would have a sharp edge. So they are smoothed out to look nicer. And maybe to simplify manufacture.

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Never know what turns up in the junk drawer. Hood from an ancient Aires (cheap 1950s leaf shutter 35) tested 90% perfect for a 135 Tele Elmar. Cant imagine what an OEM hood must cost. Maybe it would be round, and longer ? I only use old leica lenses cuz theyre small, not cuz theyre great (mostly myth). IOW this tiny hood is a great find vs OEM. Lucky me !

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MJPerini

In Cinema the device is called a Matte Box (deriving from a time when it also held 'Mattes ' like a Vignette)
They are articulated bellows affairs that move on rods . You can move the back end further from the camera (to accommodate physically longer lenses, or closer for shorter lenses. It is also equipped with french flags (like barn doors) to further block light. It takes physical plates with different apertures as well as large rectangular filters, which can be stacked.
Cinema cameras are modular, The Matte box allows nearly any lens a cinematographer chooses to use.
There are also times when a cinematographer WANTS flare for a certain shot or look, they can just dial the matte box back

Hasselblad used to make one which I still have that allowed you do dial in the appropriate length for the angle of view of the mounted lens

To be MOST effective a lens shade should be the same format aspect ratio as the camera shoots, that allows it to block the most extraneous light.
Round or petal shades work pretty well and are MUCH cheaper to make. With advances in lens coatings the lens shade is a bit less important than it once was.

RodeoMan Loc: St Joseph, Missouri

When I and probably JMatt, first saw the title of this post, we thought it was going to be about hay bales.

E.L.. Shapiro Loc: Ottawa, Ontario Canada

A properly designed, effective, and compatible lens hood is such that it is as deep as possible without vignetting for the focal length in use.

Over the years the high-end camera and lens makers produced lens shades specifically designed for each ofhte lenses. Included are Hasselbald, Leica, Nikon Canon, Zeiss, and just about all the better brands. If you buy a generic shade, you have to make certain it won't vignette- especially noticeable when the lens is stopped down.

Bellows, compendium, or matte-box-type shads are adjustable. Some are built on rails with focal length markings, and othere need to be tested by observing if there is any vignetting as you stop down the lens.