Sony FX1 vs VX2k in low light

by John Beale, Aug. 17 2005

Here is a comparison of two Sony cameras, the new HDV-format HDR-FX1 and the older MiniDV DCR-VX2000.  I chose three illumination levels of 200 lux, 30 lux and 11 lux to compare the camera's images. For reference:

The methodology was chosen based on the way I use these cameras in my event videography. You will have to evaluate its relevance, if any, to your own usage. SD is most relevant to me because I have not yet had any customer interest in HD material. Low-light operation is important since that describes most wedding receptions, and many ceremonies as well.

Sensitivity Comparison

In situations where gain-up is not used (+0 dB) and the cameras are set to 1/60 sec exposure, the FX1 requires an aperture 2.0 stops wider open than the VX2000 to achieve the same apparent image brightness (luminance).  For example, aimed at the same target from the same spot, the VX2k at f/5.6 gives 42 IRE and the FX1 at f/2.8 gives 43 IRE.  One stop is equivalent to 20 IRE units near the middle of the range, although this is not true near the black level.  The two-stop difference is not maintained when gain-up is used.

Sensitivity test target: matte white vellum on wall, flat-lit with diffused halogen lamp. Sekonic L508 spotmeter reading: EV 7.8. Both cameras manually white balanced to this target.  Video level measured at center image in IRE units, using DV firewire input to a laptop running DV-Rack Spectra 60 video analyser.

Image tests

The FX1 footage recorded in HDV 1080i (cinegamma off),  imported into Vegas 6b, converted to 720x480 (widescreen) and saved in a HuffYUV (4:2:2) AVI file format. This was in turn exported as a 720x480 PNG, and scaled to 853x480 in Photoshop to display as 16x9 using 1:1 pixels.  To match this image size, the original 720x480 DV video from the VX2k was scaled up to 853x640 which displays as 4:3 using 1:1 pixels.  For the darker two light tests, I then cropped this frame to 853x480 to match the 16x9 image from the FX1. Video captures from the FX1 show black bands on the extreme left and right hand sides of the frame (not normally visible, as they are in the TV overscan region). Video from the VX2k does not have these dark bands.

Incident exposure was measured with a Sekonic L-508 meter.  Lights were diffused 100W standard household bulbs (not halogen).

When gain is employed, each 6 dB should equal 1 f-stop. However apparently the FX1 and VX2k employ gain in different ways because the 2 f-stop difference diminishes to approx. 1 stop in dark conditions (note exposure settings in images below).

Using a sharpness setting of 12 on the FX1, exported still frames appear softer than the VX2k. This is not due to a lack of real detail, but differences in the strength of the sharpening between the two cameras. For the detail image below right, I added sharpening in Photoshop to the FX1 image to approximately match the sharpness of the VX2k image. Even after this additional sharpening, the noise level of the FX1 appears lower.  The 4:1:1 color sampling of  the VX2k DV format is most evident in the blocky texture of the rose and the boundary between the red and blue yarn samples.  It may be expected that the FX1 lens is sharper at f/4 and above than it is at f/1.7 (wide open, at this particular zoom setting).  

For all still frames on this page, the camera shutter speed is 1/60 second. The camcorder shutter speed is selectable between 1/4 and 1/10000 sec, but 1/60 sec is considered the "normal" and most frequently used setting for NTSC video.

Click on any image to view a larger version.

FX1 vs VX2k with no gain

200% detail crop from image at left

30 lux example

11 lux example

Other notes. 200 Lux image: the FX1 was zoomed in a little bit so f/1.7 was its maximum aperture at that point. The lens is rated f/1.6 but that applies only to the widest 5% or so of the zoom range. It's hard to match a VX2k shot at f/1.6 unless you use an external wide converter on the VX, because the FX1 has a wider maximum field of view.

I didn't show pictures of the blank-white-paper sensitivity test, but at least for a flat-white (or gray) field of view at the IRE 43 level the sensitivity difference is 2 stops, (f/5.6 vs f/2.8) based on my IRE measurements via DV-Rack, but I don't know how accurate and uniform the reported f-stops are.

My measurements on the 200-lux image have the VX2k image 6% or about 1/4 stop brighter than the FX1, based on the background wall. However the VX2k images look somewhat more "contrasty" than the FX1 images, suggesting either a different gamma curve shape or simply wider dynamic range on the FX1. If so then the observed sensitivity difference will be a function of the IRE level you compare: highlights, mid-grays, darks.

back to Sony FX1 page.    by John Beale