Total noob question regarding imaging.

[Defender]

Just a question regaring imaging, i keep hearing you need to expose an image for x amount of time, as a total noob, what is exposure? and why do you have to do it?, is a camera a bit like the human eye and needs time to fully grasp the scene?

PS, i told you i was a noob lol.

[jgs001]

An exposure of an image is the combination of the length of time the shutter is open, how sensitive the chip is, and the focal ratio of the lens/telescope in use. The same rules apply for daylight as for Astrophotography. During the day, however, you don't need long exposures to capture enough light on the sensor to create an image. Astrophotography on the other hand, you are capturing light, that has traveled a very long way (Light being a form of radiation obeys the inverse square law, see if I can remember it, the power of the observed radiation is the inverse of the square of the distance to the source of that radiation) from dim targets, so the actual amount of light that arrives is very small. That's why using bino's or a telescope helps you see fainter objects, as they have larger objectives than your eye, and the bigger the objective the more light they can pull in. A camera is able to capture far more of the light radiation than an eye, by keeping the shutter open (for SLR's) for a far longer period... it's a bit like a dripping tap... one drip is what the eye would see, as it's instant... but give the dripping tap an hour or two and it'll fill the sink.

HTH

[spanky]

it's a bit like a dripping tap... one drip is what the eye would see, as it's instant... but give the dripping tap an hour or two and it'll fill the sink.

HTH

That is an excellent analogy

[E621Keith]

... it's a bit like a dripping tap... one drip is what the eye would see, as it's instant... but give the dripping tap an hour or two and it'll fill the sink.

HTH

A light bucket

[stardad]

On old 35mm camera's you could change the type of film from the standard ISO100 to ISO400 or 600 for actions shots such as bike racing. You could also keep the camera shutter open for longer to let the film have more exposure.

The same applies for photographing the night sky as the only light coming is from the object you are photographing.

l