Long Exposure Not Working

[BootstrapB]

I have the latest version of picamera but can't get the long exposure to work. I'm using the recipe 3.7 listed in the docs but if I do print(camera.shutter_speed) it outputs 1705018 and if I time the length of the capture it is only about 2 seconds meaning it isn't capturing for 6 seconds. Any help would be appreciated!

[waveform80]

Hmm, can't say I can reproduce here. The following version of the low-light recipe is what I tried:

from picamera import PiCamera
from time import sleep, time
from fractions import Fraction

camera = PiCamera(resolution=(1280, 720), framerate=Fraction(1, 6))
camera.shutter_speed = 6000000
camera.iso = 800
sleep(30)
camera.exposure_mode = 'off'
print(camera.shutter_speed)
start = time()
camera.capture('dark.jpg')
print(time() - start)

And for me, this outputs:

5999884
19.7952840328

Indicating that the shutter speed is indeed ~6s (shutter speed is rarely precisely what you set as it's actually a multiple of the line read-out time) and that the capture took ~20s (which is about what I'd expect as it'll involve a couple of mode switches each of which will take at least 6s at that shutter speed, plus the capture time itself).

[BootstrapB]

Damn, when I ran that exact program it still was only taking about 2 seconds and I tried with 2 different Pi's and cameras. Which model Raspberry Pi and camera are using? I think all my firmware is up to date, but to make sure what OS are you using and which version is your firmware? Also what version of python?

Thanks!

[waveform80]

That's with a V1 camera module (can't say I've tried long exposures on a V2 yet - they're meant to be able to do 10 seconds but I just adjusted the limits in the code based on that information; it's effectively untested in picamera). The current development Pi is a 3B but most of the recipes (including this one) have been tested on a model B, and a 2B as well. The uname output is:

Linux raspberrypi 4.4.38-v7+ #938 SMP Thu Dec 15 15:22:21 GMT 2016 armv7l GNU/Linux

Python version won't make any difference (as the library is just a thin wrapper over libmmal and the same code is used for py2 and 3), but for reference it's 3.4.2.

[BootstrapB]

Turns out our firmware wasn't updated and now it works with the V2 camera. In the docs it says you can update using:

$ sudo apt-get update $ sudo apt-get upgrade

but previously that wasn't actually updating everything and instead I had to do:

$ sudo apt-get update $ sudo apt-get dist-upgrade

so you might want to consider changing that in the documentation. Thanks for the help and creating the library!

[jaimemarijke]

@waveform80 could you go into a bit more detail about the "mode switches" that cause the 6s exposure to take 20s to actually capture?

I've been trying to take 6s exposures, and with only a time.sleep(2), it takes 60s for my capture to complete. I'd like the capture time to be much closer to the exposure time, if possible.

I tried pre-empting the "mode switching" by setting sensor_mode on initialization, but that didn't make a difference.

Here's my code:

from fractions import Fraction
from time import sleep, time

import picamera
import picamera.array

start_time = time()

with picamera.PiCamera(framerate=Fraction(1,6), sensor_mode=2) as camera:
    camera.iso = 100
    camera.shutter_speed = 6 * 1000 * 1000
    camera.exposure_mode = 'off' 
    camera.awb_mode = 'off'

    with picamera.array.PiBayerArray(camera) as stream:
        sleep(2)
        camera.capture(stream, 'jpeg', bayer=True)

        print('shutter speed:', camera.shutter_speed)

        # Setting the framerate back above 1 allows camera.close() to actually succeed
        # https://github.com/waveform80/picamera/issues/528
        camera.framerate = 1

print('Elapsed time:', time() - start_time)

Output:

shutter speed: 5999976
Elapsed time: 51.01670241355896

picamera V1.13 with camera module V2.1 on Pi 3 B+