Exposure time in PiCamera not working

Question

I am trying to take a long exposure image (30 sec+) in python using a RPi HQ camera (https://raspberry.piaustralia.com.au/products/raspberry-pi-hq-camera and the PiCamera module).

This is my code:

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

tlminutes = 0.5 #set this to the number of minutes you wish to run your timelapse camera
secondsinterval = 5 #number of seconds delay between each photo taken
exposure = 20 ## this is the exposure of each image, in Seconds, between 0 and 200s

ISO = 100 ## set the ISO to between 100 and 800

numphotos = int((tlminutes*60)/secondsinterval) #number of photos to take

actualexposure = exposure * 1000000

camera = PiCamera(
        resolution=(1280,1280),
        framerate=Fraction(1,6),
        sensor_mode=3)

camera.shutter_speed = int(actualexposure)
camera.iso = ISO
sleep(60)
camera.exposure_mode = 'off'
sleep(5)
n=1
for i in range(numphotos):
    t = datetime.now()
    ti = t.strftime("%H:%M:%S")
    camera.capture(location + '/' + str(number) + '/image' + ' ' + str(n) + ' ' + str(ti) + '.png'.format(i))
    n += 1
    sleep(secondsinterval*60)

I can control the shutter speed of the camera up until around 5 seconds. If I set the shutter speed to anything more than 5 seconds, the camera defaults back to a 5 second exposure. For example, if the exposure is set to 60 s, it would only take an image for 5 seconds.

I suspect the error might be coming from the framerate, which is currently set at 1/6 fps, but if I decrease this value, e.g. to a 1/20 fps to allow for a longer exposure, I get a camera time out error.

Does anyone know the source of these issues? Or any other way that I can take a 30+ sec exposure image via the RPi HQ camera in python?

Answer 1

For the issues you are facing:

1. According to the picamera module reference, the valid frame rate for the mode you are using is 1/6 <= fps <= 1 for PiCam v1 and 1/10 <= fps <= 15 for PiCam v2. So 1/20 should not work for either.
2. According to the same reference document:

In later firmwares, this attribute is limited by the value of the framerate attribute. For example, if framerate is set to 30fps, the shutter speed cannot be slower than 33,333µs (1/fps).

Together with the first item it sounds to me like you won't be able to achieve 30s exposure in one shot. This also makes sense as the CMOS sensors differ fundamentally from CCD in their architecture.