Today’s Question: I lost the lens hood for my 70 to 200 mm F2.8 lens. While waiting for the lens hood to arrive, what precautions should I take when using the lens.
Tim’s Quick Answer: You could actually print a temporary lens hood to use while waiting for the replacement to arrive, or simply exercise caution while using the lens without a lens hood.
More Detail: First, you might consider printing a temporary replacement lens hood. You can find templates for many popular lenses at LensHoods.net (http://www.lenshoods.net). You can then print the template, cut it out, and tape it closed so that you can mount it on your lens.
The other option is to simply exercise caution while using the lens without a hood.
As a general rule, the sun is the primary light source to be concerned about, although other very strong light sources can certainly cause lens flare. The flare is only an issue when the sun (or other light source) is in front of a line parallel to the front lens element. In other words, if the sun is at least a light bit behind you, lens flare won’t be a concern because the lens will provide its own shade to the front lens element.
The key scenario where lens flare is a risk is when the sun is ahead of the front lens element but not actually in the frame of your photo. If the sun is in the frame, a lens hood won’t provide any real benefit. But when the sun is ahead of the lens but not in the frame, it can still cast light into the lens, which can then be reflected back and forth among the lens elements to create lens flare.
In these situations if you pay careful attention to the view through the viewfinder (or on the LCD display for Live View), you can simply use a hand or other object to shade the lens, blocking the light that could otherwise cause lens flare.
The key is to be aware of situations where lens flare is possible. In those situations, pay attention for lens flare, and even shade the front lens element regardless of whether you actually see indications of lens flare. Just be careful when shading the front lens element that you’re not putting your hand or other object into the frame accidentally.