Timeline for Smartphone shutter speed
Current License: CC BY-SA 4.0
16 events
| when toggle format | what | by | license | comment | |
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| Nov 16, 2020 at 0:05 | comment | added | Michael C | The "light" version of this for getting non-blurry photos of kids is to use a camera that can sync with a real flash (most, if not all, smartphones call continuous LED lights "flash", but they're not real flashes). The short burst of light from a stroboscopic flash is what freezes the motion, not the camera's shutter time. Since the flash is so much brighter than the ambient lighting, and the camera is set to expose for the light from the flash, the ambient lighting has very little influence on the resulting photo. One can even "kill the ambient" in direct sunlight with enough flash power! | |
| Nov 15, 2020 at 23:57 | comment | added | Michael C | But then again, this entire question reads like an X→Y problem. Since you haven't told us what actual photographic task you wish to accomplish with the answer to your question, we can't tell you what is perhaps a better solution than going down the rabbit hole of chasing smartphone sensor switching times. The classic solution to high speed photography is to shoot in near total darkness, leave the shutter on for comparatively long exposures and freeze motion by switching the lights on and then off very quickly. | |
| Nov 15, 2020 at 23:54 | comment | added | Michael C | @KirkHansen What you call the dominant constraint can be highly variable depending upon the intensity of light falling on the sensor. It takes some very sophisticated (and VERY expensive) lighting with highly precise triggering provided by the camera to provide enough illumination at the precise instant the rolling shutter is "on" to bring the constraint imposed by luminance down to the true limiting constraint imposed by how fast the sensor can switch on and off. | |
| Nov 15, 2020 at 23:49 | history | edited | Michael C | CC BY-SA 4.0 |
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| Nov 15, 2020 at 19:41 | comment | added | Kirk Hansen | So I think we have: • A smartphone sensor is turned ON to start accumulating photon-driven charges, and OFF to stop the accumulation. • The dominant constraint on how fast the ON-OFF interval can be is the need to collect enough photons to rise above the sensor’s noise floor. This answers my basic question, which was whether there’s a limit to how fast a given smartphone’s exposure time can be: Yes, there is a speed limit. ►►►Does anyone know where can I look up the fastest possible exposure time for a given smartphone? Or should I post this as a separate question? • • • | |
| Nov 15, 2020 at 19:38 | vote | accept | Kirk Hansen | ||
| Nov 9, 2020 at 2:50 | comment | added | Michael C | When the exposure time is shorter than the transit time, the second curtain begins closing before the first curtain is completely open. The total time it takes to make a 1/1000 exposure is the transit time (2.5ms) + the delay between first and second curtain (1.0ms), or 3.5ms. No spot on the sensor is uncovered for more than 1ms, but the photosites on one edge are exposed 2.5ms before the photosites on the far edge are exposed. | |
| Nov 9, 2020 at 2:46 | comment | added | Michael C | With long exposure times it's the same thing. Let's say we use 1 second exposure with a camera that has a shutter transit time of 2.5ms (1/400). The first curtain opens and takes 2.5 milliseconds to cross from the top to the bottom of the sensor and uncover the sensor. Exactly one second after the first curtain began opening the second curtain begins to close. It also takes 2.5ms to cross the sensor and cover it back up. Thus from the time the first curtain began to open until the second curtain completely closes is 1,002.5 ms. But no part of the sensor has been uncovered more than 1,000ms. | |
| Nov 9, 2020 at 2:37 | comment | added | Michael C | If a rolling shutter travels from top to bottom, why does this image seem to show skew in the other direction?. The video link is in the accepted answer. | |
| Nov 9, 2020 at 2:32 | comment | added | Michael C | As the first curtain continues travelling across the face of the sensor the second curtain is "chasing" it 1ms (6mm for a 24mm high FF sensor) behind. When the first curtain finishes opening, revealing the bottom of the sensor to light, the second curtain has already covered up the first 75% of the sensor. 1ms later it finishes closing to completely cover the sensor. The GIF and linked video (next comment) shows how it takes about 2.5ms (1/400) to take exposures of 1/1000, 1/2000, 1/4000, and 1/8000 by decreasing the size of the slit between the two curtains as they transit the sensor. | |
| Nov 9, 2020 at 2:27 | comment | added | Michael C | In much the same way mechanical shutter curtains in modern cameras transit the sensor at a fixed rate. It's the difference between when the first curtain begins opening and the second curtain begins following it in the same direction across the sensor that determines exposure time. At short exposure times the entire sensor is never uncovered at the same time. It may take 4 milliseconds (1/250) for each shutter curtain to transit across the sensor. If the second curtain begins closing 1 millisecond after the first curtain begins opening, the first curtain has only revealed 25% of the sensor. | |
| Nov 9, 2020 at 2:25 | comment | added | Michael C | The time difference between when each photosite is turned on and turned off is the exposure time. That is, it's the total amount of time the photosite was collecting charges.how long it takes the sensor to sequentially turn on each line on the sensor is fixed. It (usually) starts at the bottom (which is the top of the inverted image) and goes line by line to the top (the bottom of the inverted image). | |
| Nov 9, 2020 at 2:20 | comment | added | Michael C | The sensor can not be collecting photons that accumulate charges in each photosite (exposure) and move those charges off the sensior (readout) at the same time, Just like you can't pour the water out of a rainbucket into a measuring cup and catch rain falling on your yard at the same time. When a sensor is read it is "cleared" all charges are removed. When it is "turned on" it begins accumulated charges created by photons falling on each photosite. When it is "turned off" it stops accumulating charges created by photons falling on each photosite. | |
| Nov 8, 2020 at 21:43 | comment | added | Kirk Hansen | So I don’t get of on the wrong foot, could you please address my confusion on the first few sentences? 1. CMOS sensors read each line sequentially. How long each line is "on" and "off" determines exposure time. The first sentence is about reading; the second is about exposure. I’m not grasping how they relate to each other. 2. But just as with mechanical focal plane shutters, the total time needed to take an exposure is the same, regardless of the exposure time. I haven’t been able to parse this. | |
| Nov 6, 2020 at 3:24 | comment | added | Kirk Hansen | Thanks, that's helpful. It will take me a day or two to absorb it more fully, but I hope to be back on the weekend with a semi-coherent followup. | |
| Nov 6, 2020 at 2:33 | history | answered | Michael C | CC BY-SA 4.0 |