Posts Tagged ‘Pinhole camera’

Unexpected pinhole effect

21 July, 2009

You could set a pinhole up to project the eclipse onto a makeshift screen but really, the pinhole camera essentially works with any tiny hole that can serve as an aperture.

One effect to look out for is the pinhole effect when sunlight filters through any tiny gaps, including those in trees in between leaves.

Photo: Juan Jaen

This could be anything from tiny gaps in between the leaves in a tree,

Photo: Ellywa

Or a gap in a fence of wall.

Photo: Nils van der Burg

Watch out for the ad hoc and unexpected pinhole effects around you next Wednesday during the eclipse. It might create a pretty sight that is as rare as the eclipse itself.

Less than 24 hours to go!

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Viewing a solar eclipse safely, Part I

30 May, 2009

WARNING: Do not look directly at the sun with the naked eye.

Your mother, your teachers, have all told you this. And this rule still applies when it comes to solar eclipses.

800px-EclipsbrilletjeDo not look at the Sun without adequate eye protection, not even during a partial or annular eclipse, not even if you glance at it for a few seconds, because permanent damage to the retina of the eye can result due to the intense visible and invisible radiation that the photosphere of the Sun emits.

Furthermore, the retina has no sensitivity to pain and the effects of retinal damage may not appear immediately so there is no warning that injury is occurring.

Even if only 1% of the Sun’s surface is still visible, it is still 10,000 times brighter than the full Moon. And is still intense enough to cause retinal burn, even though illumination levels of your surroundings are comparable to twilight.

Sunglasses, however expensive or high quality they are, do not work and you will damage your eyes permanently. Only properly designed and certified solar filters should ever be used. 

The only time when it is safe to view the Sun with the naked eye is during a total eclipse, when the Moon completely covers the disc of the Sun. In fact, it is one of the most spectacular sights in nature.

Otherwise, here are a few good ways to 

THE PINHOLE CAMERA

The safest way to view the Sun’s disc is by indirect projection, such as the pinhole projection method, or a pinhole camera. First, poke a small hole (about 1 mm in diameter) through a piece of paper or cardboard. Let sunlight go through that hole onto a second piece of paper, cardboard or clean surface which serves as a screen. An inverted image of the Sun will be projected.

projection methodLet the pinhole be small, about 1 mm in diameter. If the pinhole is too wide, it will just be a shaft of light passing through the hole. To make the image larger, move the pinhole away from the screen.

You can make more complex versions of a pinhole camera using cardboard boxes, which are easily found on the Internet, such as this one. By the way, do not look through the pinhole at the Sun.

SOLAR FILTERS

Specially designed solar filters also allow you to observe the solar eclipse safely.

However, beware of fashioning a filter on your own. In the past, many have used one or two layers of black-and-white film that has been fully exposed to light and developed to maximum density, relying on the metallic silver contained in the film emulsion as the protective filter. However, these days, some films use dyes instead, making them unsafe.

Blackened X-Ray film may not be completely safe either, and self-made objects like a floppy dish removed from its case or the black colour slide film should be avoided.

WELDER’S GOGGLES

One of the most widely available filters for safe solar viewing is a piece of No. 14  welder’s glasses, available from welding supply stores.
 

For a more detailed explanation of observing eclipses safely, you might want to check out these websites:
NASA’s Eye Safety During Solar Eclipses
MrEclipse.com
Viewing eclipses on Wikipedia