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Edited to say: Apologies, it's sunset that these photos are being taken, not sunrise. I hope that doesn't affect the answers that everyone has taken the trouble to answer. Thanks again to all for all the advice.

Is it possible for sunlight to reflect off a 400mm camera lens, sufficient to dazzle a driver on a road approximately 300 feet away? I am not a photography buff, but my son is planning on taking some photographs at sunset which I am worrying myself sick over in case he causes an accident.

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    \$\begingroup\$ I think this question is lovely. It is still about photography but mostly is a caring question. \$\endgroup\$
    – Rafael
    Aug 31, 2023 at 20:12
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    \$\begingroup\$ Snipers sometimes rubber band a patch of dark panty hose over the enemy end of their scopes to prevent such a glare; it's invisible to the eye-end of the scope. That said, I highly doubt it's needed. \$\endgroup\$
    – dandavis
    Aug 31, 2023 at 22:08
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    \$\begingroup\$ Seems like if this were possible then car windows would be able to dazzle drivers as much or more. \$\endgroup\$ Sep 1, 2023 at 3:26
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    \$\begingroup\$ Any light reflected from the camera would be insignificant compared to driving into the sunset, which I'm sure the majority of drivers do from time to time. \$\endgroup\$ Sep 1, 2023 at 8:50
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    \$\begingroup\$ I'd worry more about making sure he doesn't look directly into the sun while taking or preparing to take his pictures. \$\endgroup\$
    – jcaron
    Sep 1, 2023 at 10:49

3 Answers 3

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If what you need is a simple answer. Do not worry about a random flare. The flare would not be different from a flare from a random car in front of a passing car.


A more detailed answer.

  1. Lenses are designed to get the light in, not bounce it. Even a flat filter in front of the lens lets most of the light pass, (let's say 99% light in and 1% reflected).

  2. Most lenses without a filter, are convex, which means that the reflection is spread almost immediately.

  3. The possibility of a flare of a flat lens hitting someone's eyes is minuscule, tiny, small. Besides that, to really annoy someone driving should be continuous light hitting for some seconds the eyes, so that means that you need to purposely move a mirror-like surface (which is not a lens) to follow your driver. Which is in fact very difficult. A small shake of your hands, a tiny angular change produces a big change in the distances.

  4. Even if this small flare gets for a moment, the time of the day means that the sun is behind the driver, so the sun is illuminating the road ahead of the driver, making any flare insignificant.


Try one experiment at home. Get one of your son's lens filters, and play with it trying to hit that reflection in a specific target, Depending on the conditions you will not be able to find the reflected beam even at a couple of meters away.

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    \$\begingroup\$ The front element of a 400mm lens is likely convex (mine is). In reflection that will spread the light out compared to a flat surface, weakening it. Even with flat glass, the flare would be different to that from a random car: from the lens it would be far weaker. \$\endgroup\$
    – Chris H
    Sep 1, 2023 at 10:51
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    \$\begingroup\$ I added that point, clarifying "with a filter and without". \$\endgroup\$
    – Rafael
    Sep 1, 2023 at 12:17
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Absolutely don't worry about it. At all. Rafael's answer is perfect, but I just want to add some extra context.

I used to commute every morning directly west over a bridge from a barrier island on Florida's east coast, with very few tall buildings on the island to block the morning sun behind me. The bright sunrise was behind me, but annoyingly, it reflected off of two main things:

  • the tall office building with mirrored glass windows at the west end of the bridge, effectively putting the sun directly in front of me; and
  • the slightly convex rear window of the car in front of me. Because we're both moving at the same speed, once the sun reflected off the window into my eyes, it was like having a mirror mounted directly in front of my car, pointed at my eyes.

Your son is causing neither of these conditions. The building is like a massive mirror, meaning I saw the sun "travel" across it for a long time while it reflected into my eyes.

  • Your son's lens's front element, probably about 100mm diameter at most, at 300 ft is actually smaller than the sun's apparent angular diameter to our eyes. Meaning, at 300 ft, your son's lens isn't even reflecting the entire area of the sun.

But more importantly, if his lens did reflect the sun into a driver's eyes, it's only for a vanishingly small moment, as the driver traverses into the narrow reflection path, and then immediately out of it.

And finally, if your son's lens has a lens shade, that will help reduce incidental reflections into other people's eyes even more.

But truthfully, don't worry about it at all. Any reflective glass or polished metal surface larger than your son's lens's front element is a bigger risk of dazzling glare to drivers than his lens is.

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One thing not yet mentioned in the other answers.

I have never seen a lens where the front element is flat. I only know lenses with a convex front. So, the reflection from the front element isn't concentrated in one direction, but spreads out over quite some angle, thus being much less intense than a flat-mirror reflection. (And according to my experience, the same is true for reflections from inner lens surfaces.)

If a driver gets disturbed by such a reflection enough to cause an accident, then I'd see it as the driver's fault (central-european point of view, different legislations might disagree).

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    \$\begingroup\$ A couple of «photography buffs» I know keep an UV filter mounted, perhaps by tradition. For them, it is an affordable protection of the lens against dry fine grains of dust, especially during summer time while hiking, and a little bit of mechanical protection, too. To block this part of radiation was a tool more frequently seen for the analogue technique (then sometimes sold as sky light filter), than now for the digital one. \$\endgroup\$
    – Buttonwood
    Sep 1, 2023 at 8:35
  • \$\begingroup\$ @Buttonwood That's correct, I didn't think about that. UV filters (like all other kinds of filter) have a flat surface. \$\endgroup\$ Sep 3, 2023 at 13:36

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