Movies with the SD800  (continued)

 

Low Light Tests with Motion


I used an indoor setup of a tabletop scene, which included some small mobiles, to test how the SD800 camcorder performed in relation to smoothness of motion, colour rendition and noise as the lighting level was reduced.  I used a tripod and took the clips in iA (auto) mode and 1080/60p at a range of lighting levels with the zoom set at full WA (35mm FL) so that the widest available aperture was f/1.5.


I measured the illuminance of the scene in lux at each lighting level using an incident digital lightmeter.  (One Lux is defined as the illuminance at a point on a surface which is one metre from, and perpendicular to, a uniform point light source of one candela.  A single candle emits light with a luminous intensity of roughly one candela.)  With this setup, I found that the camcorder in iA mode automatically changed from iA to the candle symbol ("Low Light" mode) when the scene illuminance was reduced to 3 lux or below.


I used iMovie to edit the clips which were taken at illuminance levels of 200, 32, 12, 6 and 3 lux. During the editing I slightly altered the levels and the white balance to optimize each clip, and I added a soundtrack since the clips were otherwise silent.


To give an idea of typical illuminance levels, the minimum level for reading is about 150 lux.  Most homes, warehouses and theatres have lux levels around 80-150.  Offices have lux levels of about 250-500 lux.  Twilight is 1 lux, and good main road lighting at night provides about 15 lux.


The movie can be viewed at: http://vimeo.com/24345645


As can be seen, the motion is quite smooth at illuminance levels from 200 down to 6 lux.  There is a gradual loss of colour rendition as the lux level decreases, and noise is visible although not very obtrusive in the 12 and 6 lux clips, but becomes more evident in the 3 lux clip.  Scenes with more extensive dark areas than in the setup that was used would be expected to show more obtrusive noise at the low illuminance levels. 


Motion Smoothness

At 3 lux, as noted above, the iA mode changed to the "Low Light" scene mode, and some trailing can be seen in that clip, especially in the motion of the large mobile with spheres.  The owner's manual says that in this mode the shutter speed is 1/30s or more.  For all the other clips where the illuminance was 6 lux or above, the shutter speed was 1/60s and thus the motion was smoother.  However, for low light situations where there is little or no movement, using the "Low Light" Scene mode can be a useful way of increasing the exposure through a slower shutter speed and thus improving video quality.


Colour Rendition

Regarding the colour rendition, although this becomes poorer in the clips at low illuminance levels, at these levels the scene also visually becomes quite dim to the eye, and the apparent visual colour saturation in the scene also decreases.  This is because the color experience of light and objects changes in dim light as the eye changes from trichromatic vision to monochromatic vision.  Taking this into account, the clips can be considered to simply mimic how the eye also views the scene as the illuminance becomes very low.


Widest Available Aperture

An important aspect to recording low light scenes is the widest available aperture.  The zoom lens in the 900 series camcorders, which is the same as that in the 700 series, changes from a widest available aperture of f/1.5 at full WA (35mm FL) to a widest available aperture of f/2.8 at the maximum optical zoom setting (420mm FL). Thus there is a 2 stop (2 EV) range in the widest available aperture as the lens is zoomed between the extremes of focal length.  As a result, the best sensitivity in low light situations is achieved at full WA, and the sensitivity necessarily falls as the lens is zoomed towards full tele.  Hence, if possible, it is better when shooting in low light to approach closer to the subject and shoot at wide angle rather than from further away and zoomed in.  This aspect tends to be overlooked in reviews, which in their low light tests generally do not even specify the focal length that was used.


Shutter Speed and Iris Settings

In the iA mode for both the 900 and 700 series camcorders, the shutter speed and "Iris" (aperture and gain) are adjusted automatically.  With the cam in iA mode and held steady without changing the zoom setting, when the "Manual" button is pressed the shutter speed and iris settings used by the iA mode can be read.  However, there are intermediate steps in the settings (as well as the automatic operation of internal ND filters in bright light) which are not shown on the display, thus the display reading for gain is only approximate.  Also, in the "Low Light" Scene mode, the shutter and iris cannot be changed manually and therefore the figures are not shown.  Nevertheless, the readings where available can be indicative and so I recorded them when carrying out the tests, and I have provided them below:



Still Shots

In low light situations where there is no motion, greater EV sensitivity can be achieved by using the camcorder in still image mode.  In stills mode the shutter speed can be much slower as it is not confined by the requirements of video fps.  I have routinely taken hand-held still shots at 1/10s with sharp results in situations such as in dimly lit museums.  This holds even when partly zoomed in and thus at narrower apertures than f/1.5.  I have used the stills to make slide show movies at 1080/60p, as shown with the SD700 here.



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