Why not the darkness captured when the shutter closes?

[gregtallica]

I hate it when people turn off the poser.

I think it's more annoying when some people can't turn the poser off.

 

[VanGogh121]

I'm amazed, that this thread has gone three pages.... If a bear Sh!ts in the woods and no one is around to hear it is it a chicken or an egg?

 

[KmH]

Well then if the exposure can be controlled without a shutter, why have one? What is the benefit of augmenting an electronic device with a mechanical one, which will eventually fail?

Because the shutter allows some other tasks to be performed, like syncing the flash of light to the moment the front curtain is fully open, or to the instant the rear curtain begins to close.

Also features llike long exposure noise reduction require powering up the image sensor and making an equally long exposure with the shutter closed so the camera CPU can map the dark current noise of the image sensor.

 

[cgipson1]

I hate it when people turn off the poser.

I know some posers I would love to be able to turn off!

 

[sashbar]

Well then if the exposure can be controlled without a shutter, why have one? What is the benefit of augmenting an electronic device with a mechanical one, which will eventually fail?

Because the shutter allows some other tasks to be performed, like syncing the flash of light to the moment the front curtain is fully open, or to the instant the rear curtain begins to close.

Also features llike long exposure noise reduction require powering up the image sensor and making an equally long exposure with the shutter closed so the camera CPU can map the dark current noise of the image sensor.

The other reason is a mechanical shutter eliminates the need for added electronics at each pixel location of a sensor that would be used to turn on/off the pixel and store the charge. It allows to use a more efficient sensor with a higher fill factor.

 

[amolitor]

It IS captured! Your sensor captures darkness constantly. Luckily, it's very efficient at storing it. Still, from time to time a pixel will overflow, and you'll get a spot of darkness on the sensor or even several, and then you have to clean it.

As has been noted, it's only when the power on is on, though. So, whenever your camera has been turned on for more than an hour or so total, you should point the lens at the ground, so the pixels can empty out, and tap the camera lightly but firmly on the back with the heel of your hand. This will knock the darkness out of the sensor and safely into the dark trap on the back of the mirror.

 

[Josh66]

Photography 101.6 ? Shutter

That website has a pretty good animation of a shutter working. If you scroll down a little bit (figure 1.6.2), to the part where it shows three different speeds ('slow', 'medium', and 'fast'), it gives you a pretty good idea of how it works.

The "slow" speed shown is the x-sync for that imaginary camera. X-sync is the fastest speed where the sensor or film is fully exposed (neither curtain is covering the sensor), typically 1/200 or 1/250.

 

[Trblmkr]

Since the sensor for our digital cameras is electronic. Wouldn't the correct answer be to the OPs question be. No power is applied to the sensor once the shutter is closed.

 

[EDL]

Sensors don't require absolute darkness to not record anything. It takes a certain amount of photons to "register" and create a signal that will show something.

 

[Derrel]

This thread makes me think of these fine folks...Eric Clapton? No, Lens Scapon | Mail Online

 

[TCampbell]

There are cameras that have "electronic" shutters where no physical shutter blocks the sensor. DSLRs use physical "focal plane" shutters which physically slide across the image.

On a digital camera, the sensor is covered with "photo sites" which you can basically think of as an array of "photon counters". They count the number of photons that hit that particular spot. If one photo-site is hit by 10 photons and another is hit with 5 photons (I'm exaggerating to describe the concept -- in reality there are MANY more), then the point hit by 10 will register as being "twice as bright". When the exposure completes, the camera will "read out" the data from the sensor and count all the scores for each pixel. On a color camera the "photo-sites" are covered with an array of tinted boxes called a "Bayer Mask" -- some boxes are tinted green, some red, and some blue. The camera compares the number of red, green, and blue in any given area to decide the overall final "color" for that "pixel" (a single "pixel" in a color image is really composed of four of those colored "photo-sites" on the sensor.)

This whole process is "additive". As additional photons arrive, it increases the count at the location on the sensor where those photons hit. It's not an "averaging" system... meaning if the light is blocked but the seconds continue to tick by there's nothing that says the "average number of photons per second" was reduced because the shutter was closed but the camera was still counting off time (if it worked that way, then the photo would start to get darker). Since it's additive... the amount of time the sensor is technically still "on" but blocked by the shutter will not affect the final image.

 

[MLCIII]

Well said, TC. The "additive" part is key.

Eric Clapton reminds me of Michael Bolton, and Michael Bolton reminds me of this...

 

[k.udhay]

Hi. Thanks to all of you. I am very sorry for a delayed reply.
I got it clearly now. I just did one exercise to check it. After keeping a very slow shutter speed (4s), I closed the lens with its cover before the complete shutter duration is over. Surprisingly, I did NOT get a pitch black photo! Hence, I paraphrase what I understand as "the camera captures only light and not 'absence of' light." Thanks again!