A little script for testing what happens when you fiddle with the Pi camera module's gains and shutter speed

fiddle_gains.py

from __future__ import (
    unicode_literals,
    absolute_import,
    print_function,
    division,
    )
str = type('')

from picamera import PiCamera
import curses

def main(window):
    window.nodelay(True)
    camera = PiCamera(resolution='VGA', framerate=30)
    camera.start_preview()
    while True:
        window.addstr(0,  0, 'Analog gain:    %-8.3fx' % camera.analog_gain)
        window.addstr(1,  0, 'Digital gain:   %-8.3fx' % camera.digital_gain)
        window.addstr(2,  0, 'Exposure mode:  %-5s' % ('fixed' if camera.exposure_mode == 'off' else 'auto'))
        window.addstr(3,  0, 'ISO:            %-5d' % camera.iso)
        window.addstr(4,  0, 'Shutter speed:  %-10.3fms' % (camera.exposure_speed / 1000))
        window.addstr(5,  0, 'Shutter mode:   %-5s' % ('fixed' if camera.shutter_speed != 0 else 'auto'))
        window.addstr(7,  0, '1 = Set ISO 100')
        window.addstr(8,  0, '2 = Set ISO 200')
        window.addstr(9,  0, '4 = Set ISO 400')
        window.addstr(10, 0, '8 = Set ISO 800')
        window.addstr(11, 0, '+ = Increase shutter time')
        window.addstr(12, 0, '- = Decrease shutter time')
        window.addstr(13, 0, '0 = Auto shutter time')
        window.addstr(14, 0, 'A = Toggle AGC')
        window.addstr(16, 0, 'Q = Quit')
        window.refresh()
        try:
            key = window.getkey()
        except curses.error:
            continue
        else:
            if key in '1248':
                camera.iso = {
                    '1': 100,
                    '2': 200,
                    '4': 400,
                    '8': 800,
                    }[key]
            elif key in 'aA':
                camera.exposure_mode = 'auto' if camera.exposure_mode == 'off' else 'off'
            elif key == '0':
                camera.shutter_speed = 0
            elif key == '+':
                camera.shutter_speed = min(1000000, camera.exposure_speed + 100)
            elif key == '-':
                camera.shutter_speed = max(1, camera.exposure_speed - 100)
            elif key in 'qQ':
                break

curses.wrapper(main)

SSH into your Pi and run the script from there, so you can see the controls and the preview at the same time. If you haven't got a spare machine to SSH from, add something like alpha=192 to the start_preview() call so you can see the controls. Now, fiddle!