There are several types of sensors but the most basic differences are
seen between what are called "full frame" sensors (which, in this
context, has nothing to do with size) and "interline" sensors. Full
frame sensors are what are used in DSLR's and interline sensors are used
in video cameras, point and shoot cameras and especially P&S cameras
that have a movie (video) mode.
A full frame sensor is called that because it captures the entire frame
all at once. It requires a mechanical shutter to protect the sensor
from light. When the shutter is closed the electrical charge is drained
from each pixel. When the shutter is opened light strikes the sensor
and each pixel receives an electrical charge. When the shutter is
closed the camera reads the data from every pixel on the sensor all at
the same time (conceptually anyhow) and drains the charge in preparation
for the next exposure.
An interline sensor operates a bit like your computer monitor painting
the screen which is done line by line. The interline sensor uses an
electronic shutter and turns individual lines of pixels on and off in
succession. It can run continuously by scanning lines from top to
bottom and then starting all over again. The display circuitry can read
these lines continuously and also paint them on a display screen
continuously. This is what makes a live image or... video/movies. Note
that if the frame rate is, say, 30 frames per second then the last row
of the image was exposed 1/30th second after the first row. If the
image is moving then there may be motion blur from the delay. Full
frame sensors don't suffer from this problem and have fewer other
drawbacks as well. The interline sensor's biggest problem is that the
design uses a large amount of the surface area of the sensor for the
shutter and read-out circuitry. The interline sensor may have only 25%
of the available surface area to catch photons so they are inherently
noisier than full frame sensors.
Got the picture? If you want a live image you want interline. If you
want a low noise, high quality image you want full frame. Can someone
make a sensor with the qualities of both? They're trying but I don't
think anyone has succeeded.
Chuck Norcutt
Candace Lemarr wrote:
>
> ----- Original Message -----
> From: "Moose"
>
>>I'll try. The real time image you see on the LCD in A mode comes from a
>>separate small sensor behind a partially silvered mirror in the
>>viewfinder, not from the actual picture taking sensor, which is behind
>>both the mirror and shutter.
>>
>>In B mode, the main sensor is working as a live view sensor. However,
>>when you take a picture, the shutter closes, the sensor resets, the
>>shutter operates at the selected shutter speed, an image is captured,
>>and the shutter opens again with the sensor in live view mode.
>>
>>It's pretty clear that the sensor isn't capable of simply grabbing one
>>of the live view frames as they go by.
>
>
> Ok, that makes sense. Thanks for putting it simply :-)
>
>
>
>
>>There are some tech reasons I
>>understand, and some I don't, but lets just leave it that the current
>>sensor can't do what is needed.
>
>
> God bless you for leaving it there, LOL...I wouldn't understand it if you
> told me more. :-D
> Thank you, Moose :-)
> Candace
>
>
>
>>Moose
>>
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