Camcorders with CMOS sensors

[Dan Robinson]

Just an FYI for any chaser considering a digital camcorder using a single CMOS imaging sensor rather than a CCD. The new HDR-HC1 HDV camera from Sony is one. The CMOS sensors record using a 'rolling scan' of the chip per frame, grabbing single horizontal lines in a 'sweep' of the chip - rather than grabbing the entire frame image from the chip simultaneously as a CCD does. This results in some anomalies in that fast-moving subjects will appear slanted. Sudden bursts of light, such as from a lightning strike or a camera flash, will only be recorded on a portion of the frame.

This should be of concern to a chaser considering this type of video camera, since it does not do well with lightning.

From a post on DVInfo.net:

From page 87 of the HC1 manual (PDF out on sonyhdvinfo.com), it says "subjects passing by the frame might appear crooked". This suggests that the CMOS sensor is using a rolling shutter rathar than a global shutter. If true, it would mean that Sony is getting more light sensitivity out of the available die space on the sensor by not having an extra shielded sensor area dedicated for a virtual shutter. The drawback is that objects in rapid horizontal motion show up tilted. The faster their CMOS readout speed can be, the less tilted it will be overall, but still it would be present. This same effect, much more pronounced, can be seen with cheap webcams when there is horizontal motion in the scene. In that scenario you can clearly see the scanning effect being used by the sensor.

Here are some links:

http://www.gyhduser.com/showthread.php?p=876#post876

http://www.sonyhdvinfo.com/showthread.php?...light=lightning

http://www.sonyhdvinfo.com/showthread.php?...light=lightning

http://www.sonyhdvinfo.com/showthread.php?t=2688

http://maisonbisson.com/blog/post/10531

 

[Bill Hark]

Dan, thanks for the info. I had been concerned about low light sensitivity in the new HD models and didn't even consider problems with CMOS. I hope this type of imaging doesn't become the only type avaliable.

Bill Hark

 

[Dan Robinson]

The good news is that the higher-end models, the HDR-FX1 and the pro version HVR-Z1, are 3-chip cameras with standard CCD imaging sensors, so they do just fine with motion and lightning. The FX1 however costs $3200, while the CMOS HDR-HC1 sells for under $2K. The HC1 is small, about the size of a TRV900. The FX1 is a pretty big camera, larger than a VX2100.

While the HC1 is cheaper than the FX1, it has some issues besides the CMOS shutter problem that would make it a less-than-optimal chasing cam. For example, it has the dreaded bottom-loading tape door that requires the removal of the tripod shoe just to change the tape.

As for low light, the FX1 and Z1 are rated at 3 lux, which is slightly better than the TRV900 (4 lux) but not as good as the VX2100/PD170 (1 lux).

So, the FX1 and Z1 would be decent for chasing, but the HC1 is probably one to avoid for storm shooting.

 

[Stuart Robinson]

I agree Dan – the HC1 is just too small and most of the adjustments are via the touch screen LCD panel, also there is no easy way to get an infinite focus – But due to its small size the HD1 would make for a good dash cam.

I run with a FX1 and while it is a big camera the 3CCD quality of shots that it takes are stunning! – I really like all the external buttons which can be reached when you are in a hurry.

Having only owned the FX1 for a month or two now I have only chased hurricanes with it – the 3 LUX low light does not seem to be a big issue but I would like to try and capture some lightning with it before I pass further comment.

 

[Dean Gill]

Originally posted by Stuart Robinson
also there is no easy way to get an infinite focus .

I own a HC1 as a dash cam and must admit I noticed these anomalies on fast-moving subjects and lightning. However, it's not systematic, it's only visible on one frame out of three. As for the infinite/manual focus, there is an external switch for it, there is no need to go through the lcd screen menu...