| Author | Thread |
|
|
12/15/2004 03:17:36 PM · #1 |
I'm not super familiar with digital camera technology thus I have a couple of possibly outlandish questions.
Why do digital cameras need a shutter to control exposure? Couldn't you electronically control the sensor for exposure time? Like turn it on or off for the required exposure time. Without a shutter wouldn't it improve such things as flash coordination?
Another question is wouldn't it be possible for digital cameras to auto bracket a shot within the same frame? Say for instance for an exposure calling for 1/125 the camera would start the exposure then bookmark sensor measurements at 1/250, 1/125, and 1/60. Then create 3 different files from the "same" exposure. |
|
|
|
12/15/2004 03:21:32 PM · #2 |
Most DSLR's do have Auto Bracketing, on the 300D it fires of 3 shots 1 at the exposre you have set , 1 under and 1 over. Its not related to the shutter speed but the f stop.
mike
|
|
|
|
12/15/2004 03:22:57 PM · #3 |
My (limited) understanding of CCD/CMOS technology is that the photons striking the chip result in built-up (stored) electric charge (basically stored electrons) and that the chip has to be "emptied" before it can store another image/charge.
edit: typo and this is strangeghost posting on my daughter's account.
Message edited by author 2004-12-15 15:44:52. |
|
|
|
12/15/2004 03:25:18 PM · #4 |
When the values are read out of a CCD the stored charge has to be dumped out of each cell to be read.
In other words you can read out a pixel with out destroying the data in it.
In theory a CMOS sensor might get around this but you run into a second problem, it take a fair bit of time to read out the contents from the cells, much longer then a typical exposure.
As for the first question my guess is that the shutter is needed to avoid blooming, again it take a fairly long time to read out all the pixels and during this time there can me leakage from the pixels to the CCD that is transferring the data. For a CMOS sensor I would think you would always need a shutter.
This most likely is more confusing then help.
|
|
|
|
12/15/2004 03:32:45 PM · #5 |
Originally posted by MikeOwens:
Most DSLR's do have Auto Bracketing, on the 300D it fires of 3 shots 1 at the exposre you have set , 1 under and 1 over. Its not related to the shutter speed but the f stop.
mike |
Yes, I'm aware of that feature but that's 3 diferent shots from my understanding and that uses f-stops. I'm wondering can they do it from a time perpective. What you get now from a time perspective is 1/125+1/125+1/125+any additional shot to shot time(?). I'm wondering if you could just take one total time exposure of 1/250 and somehow digitally bookmark sensor readings within that exposure at 1/60, 1/125, and 1/250 and create 3 files from that. The comment mentioned about dumping might explain why it can't be done. |
|
|
|
12/15/2004 03:36:24 PM · #6 |
Sorry, missunderstood you.
Mike
|
|
|
|
12/15/2004 03:44:51 PM · #7 |
Originally posted by scottwilson:
In other words you can read out a pixel with out destroying the data in it.
|
Man, then it's like quantum physics. I didn't realize the process to read the sensor was so slow. |
|
|
|
12/15/2004 03:47:35 PM · #8 |
Originally posted by dsb_mac:
Man, then it's like quantum physics. I didn't realize the process to read the sensor was so slow. |
I don't think it's slow, it's just that there is no way to read the charge in each cell without letting the little buggers out (the electrons).
Here's a website with a decent explanation of how the sensors work:
Click
Message edited by author 2004-12-15 15:50:16. |
|
|
|
12/15/2004 03:55:46 PM · #9 |
| My thinking is a result of reading too many "Learning Exposure" books and thinking how it exposes on film. They usually use the water analogy filling a cup. So I'm like "Why don't they just see what the water level is as they fill the cup?". I didn't realize in digital's case you couldn't see the cup until you've finished filling it. |
|
Home -
Challenges -
Community -
League -
Photos -
Cameras -
Lenses -
Learn -
Help -
Terms of Use -
Privacy -
Top ^
DPChallenge, and website content and design, Copyright © 2001-2025 Challenging Technologies, LLC.
All digital photo copyrights belong to the photographers and may not be used without permission.
Current Server Time: 09/13/2025 05:22:51 PM EDT.
