What does the camera do when you take a picture?

Started by csg2, September 07, 2018, 06:06:18 PM

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csg2

Hi folks,

So what does the camera do when you press the shutter or trigger an exposure with an intervalometer?

I have been trying to stack images of the moon and been plagued by blurry shots. Out of curiosity, I got an accelerometer to measure the vibrations the camera was making. With a mirror lens, and therefore no shutter, there appear to be 4 motions. I guess this is
1. Mirror up
2. Light curtain?

Exposure

3. Light curtain?
4. Mirror down

Is this right?

What about the electronic part of the process?

If there is an post somewhere about this I would be glad of a pointer.

For ref I have a 550D.

a1ex

FYI, there is a not-so-well-known feature that lets you tweak the delay between mirror/shutter going up and exposure starting. Looks like it's enabled on 550D (look for MLU_HANDHELD). Didn't touch it for years.

https://www.magiclantern.fm/forum/index.php?topic=3236

If you are interested in software details:
https://www.magiclantern.fm/forum/index.php?topic=1915.0

And some low-level details on exposure timings on the full-res silent pictures thread. TLDR: exposure starts on all image rows at the same time (electronic shutter), but ends at different times (rolling shutter - top ones are read out first, bottom ones are read some hundred ms later).

So, the purpose of your mechanical shutter is to prevent this gradient at the end of the exposure (and allow fast shutter speeds). You can delay the start of the exposure as much as you want, as it starts on all rows at the same time.

And if you are interested in a totally silent full resolution readout, but with rolling shutter (we call that "full-res LiveView"):
https://www.magiclantern.fm/forum/index.php?topic=19336.0


Levas

I somewhere learned that if you want to have as little movement as possible by camera shutter/mirror mechanism, you must shoot with liveview on.
Canon camera's are said to use electronic first curtain when shooting with liveview on.
So only movement is your second curtain closing at the end of the exposure time.

When not in liveview, you first get the mirror moving up, causing shake.
Then the first curtain drops, causing a second shake.
After that second curtain drops.

So for crisp sharp images on Canon DSLR's, shoot with liveview on 8)