Tuesday, April 15, 2008

Robin's Hood

Many photographers who are puzzled over the hood issue get confounded even more when the world moved from film to the digital world. Do we really need a hood around the front end of a lens? Why can't an expensive lens take care of it without a hood? What's the reasoning behind it?

Let me start with a real life example and I assume that you do drive a car. Imagine yourself driving through a dark tunnel. When you are in the last 200-300 yards inside the tunnel, looking out from inside the tunnel, what do you see? You will notice that the scene outside the tunnel is crisp and almost sparkling clean. When you get closer to the edge of the tunnel, you notice that the crispness of the scene outside is reduced. When you finally approach the very exit of the tunnel, you will feel the crispness of the scene dropping by a large fraction compared to what you originally saw while you were deeper in the tunnel? Check it out next time when you drive through that tunnel!

That crisp image you saw while inside the tunnel is synonymous to what your film or digital sensor sees with the lens hood attached. Basically, the lateral light hitting the front element of the lens is blocked out by hood: a lot of it is blocked. When you are about to exit the tunnel, the lateral light begins to pour in from all directions, interfering with the relevant light from your subject that is entering your eyes (the lens). This effect lowers the contrast of the image cast on your retina and reduces the crispness of the edges of the subject you are looking at, too. This lateral light interference plagues film and digital sensors.

There's no lens I know of in the market that can reduce this effect without a hood. This is exactly the reason why you should get a hood even if the lens does not come with it. In general, it will give you a better image almost all of the time. Actually, right now, I cannot think of a situation it won't.

Happy hooding and don't take Robin's.

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