[heartbreak]

Just to clarify, there’s no concentration of energy involved with the eclipse itself. The concentration involved is no different than setting a leaf on fire with a magnifying glass on a regular day.

The sun isn’t a garden hose. Putting something in front of it doesn’t make the edges more intense.

[mikeash]

There kind of is, because it's darker when the sun is partially covered, so you'll use a larger aperture or longer exposure than you would normally. This is also why it's more dangerous to look at the sun during an eclipse than it is normally: your iris opens wider during an eclipse because it's not as bright.

[nolok]

I think you misunderstood his point, which was: there is no more energy coming from the sun at any given point during the eclipse than in a clear day. The sun isn't "sending" more energy on the path that aren't blocked, nor is the energy blocked going around the obstacle and concentrating on the areas still visibles.

The reason for the damage is entirely due to the receiver behaving/being differently, be it your eyes or your camera, because they get tricked into thinking it's dark and they act like it, being much more receptive and then overwhelmed.

[howlgram]

"tricked into thinking it's dark" is kind of misleading, because it is in fact darker, but for some reason unknown to me there the energy from the sun harms you as much. I thought the issue with looking at its sun was its brightness, but i guess it isn't?

[Stratoscope]

During a partial eclipse, part of the sun is hidden behind the moon. So the overall amount of light reaching the ground around you is indeed less, in direct proportion to the amount of sun that is eclipsed.

For example, if 90% of the sun is covered by the moon, then only 10% of the usual amount of sunlight will light up the area around you. So it is quite a bit darker than usual.

However, the portion of the sun that is still visible is just as bright as it would be on any other similar day. If you stare at that remaining portion of the sun, or aim a camera at it, it will cause the same damage as it would any other time, only in a smaller crescent-shaped area instead of a full circle.

The danger to your eyes is even greater, because the overall darkness tricks your irises into opening up wider and letting even more light in than usual.

You're pretty unlikely to stare at the sun for 30 seconds on a normal day. But people do that during a partial eclipse, and that's the problem. Similarly, people don't usually aim their cameras directly at the sun with the lens wide open and no solar filter - except during an eclipse.

A total eclipse is quite a different thing, of course. During totality, the sun's bright photosphere is completely hidden, and only the much fainter corona is visible. This is only about as bright as a full moon, and it's perfectly safe to take pictures with any lens, and to observe directly with the naked eye - even with binoculars.

[animal531]

So I could shine a flashlight into my eyes while looking at the eclipse, and I'd be ok?

[mysterypie]

That's one of the best explanations I heard about why and how the eye damage can occur. I'm curious how far can you carry that reasoning: If 99.9999999% of the sun were covered during a partial eclipse (down to a single stream of photons), does it damage one single rod on my retina as opposed to a crescent-shaped region? I'm guessing that a single stream of photons from the sun doesn't have enough energy to do any damage.

[Stratoscope]

Now that is an interesting question!

Anecdotally, I viewed the 1979 total eclipse with binoculars (and no filters), and at the end of totality I continued to look through them for a few seconds to see the diamond ring and Baily's beads.

It didn't harm my vision at all, even though there was some fair amount of direct sunlight coming through by then. But it was only a few seconds. The duration of sun exposure certainly is a factor.

[mikeash]

The issue is how much light gets focused onto a small area of your retina. When the sun is partially eclipsed, the darkness makes your iris open up to let more light in. That then focuses more light from the visible part of the sun onto the same area of retina.

[rbobby]

Your iris reacts to visible wavelengths and not ultraviolet wavelengths. So your iris is open much wider than it ought to be given the amount of UV present (especially given that UV is much more damaging than visible). If you see what I mean :)

[Coincoin]

It is brightness, but brightness at a single focused point, not total brightness.

[nickrio]

> because they get tricked into thinking it's dark and they act like it

This is a really bad example :DDD

I don't think that is totally true for human eye. You can test it by putting a LED spotlight in front of you at night, and have someone else check your pupil before and after you turn on the LED (And remember test it in different distances).

Camera works differently, they have multiple ways (Metering Modes) to test the brightness of a scene. So how it work will depends on the selected Metering Mode.

And camera can collect more light by letting light keep entering the light sensor for longer time. Plus, bigger lens can also collect more light, some people may even mount their camera on a telescope, thus more light entering. So maybe this is the physical reason why so many gears got destroyed?

[mikeash]

I understood the point just fine. My point is that there is a greater concentration of energy which is what causes damage, it just happens in the optics rather than at the source.

[triggermuch]

i was always wondering how a pin hole protects you, and i mean im sure i could have looked it up but just, really wasnt important. dude that tid bit made my day - the more you know

[resoluteteeth]

Dingaling is talking about the light being concentrated on certain areas of the sensor. Because the total/average brightness is low, the exposure ends up being much longer then at normal conditions, causing damage to the areas where the light is concentrated. Under normal conditions, the light will be less concentrated on certain spots, so even though there is much more light in total, the camera will choose an appropriate exposure that will prevent damage to the sensor.

[klodolph]

You'd have to be incompetent to trust autoexposure during an eclipse.

[Gracana]

> The concentration involved is no different than setting a leaf on fire with a magnifying glass on a regular day.

That's what they're saying. Zooming in on the sun vs the sun happening to be in-frame.

[xsmasher]

Are you saying zooming in on the sun makes damage more likely?

Wouldn't zooming in spread the sun's energy across more of the sensor? Same energy, larger area = less intensity.

[grahn]

The irradiance is determined by the aperture, which is measured relative to the focal length. So with e.g. f/2 you get the same heating of a given area of the sensor regardless of the focal length (i.e. "zoom").

Put differently, longer lenses typically also have bigger absolute apertures, collecting incident light from a larger cross-section. This compensates for the fact that a given solid angle of incident light is spread over a larger area of the sensor.