On 29 Aug 2000 22:40:57 GMT, lawrence@vex.net (Lawrence Kwan) wrote:

>In article <25010-39ABDADE-31@storefull-148.iap.bryant.webtv.net>,
>Steve McDonald wrote:
>>The TRV20 has more than a million pixels on its 1/4-inch CCD, and the
>>340,000 of them that are actually used for motion video are much smaller
>>than the pixels of the TRV520, which has 460,000 total pixels, also on a
>>1/4-inch CCD with 290,000 of them used for the picture....
>> Even though the TRV520 has fewer pixels, they are more than twice
>>the size as those of the TRV20. Also, the active pixel area of the
>>TRV520 is almost twice the size as that of the TRV20, when the latter is
>>used for motion video.

>This is not correct. Actually, both and TRV20 and TRV520 have similar
>light capture area on the CCD. TRV20 has a 1,070,000 pixel CCD of which
>690,000 are "effective pixels". Both are 1/4" CCDs and both use about 63
>to 65% of the CCD area for light capture for the actual video frame.

Ummmm, I think SL is correct...
With the PC-100 and TRV-20, the chip sizes are the same as
most consumer-level camcorders, but the large pixel-count is
used for the still images only. Out of those large
pixel-count small chips, a smaller area is considered
"active" for video purposes - but of these, a smaller yet
number actually form the video image due to the requirements
for the digital stabilizer for the PC-100/TRV-20 and the
(I assume, but possibly not...) optical stabilizer of the
TRV-520. As a result, the *pixel size* and image area used
by the PC-100/TRV-20 are both smaller. Add to this: the
chip types are different (as are, most likely, the set-ups
for sharpening and contrast), and I would be surprised if
the pictures looked the same...

>>This is why the image from the TRV520 looked so much better in the
>>limited indoor lighting of the store. Bigger pixels, with a larger
>>sensing area, give better, brighter pictures in dim light.

This is correct, chip-types being the same (though they aren't...).

>No, TRV20 has more densely packed and smaller pixels, but the total
>effective light capture area is similar (larger number of pixels making up
>for the smaller size of individual pixels). However, the capability or
>the light sensitivity of the two different CCDs may well be different.
>But another key factor is the optics. TRV520 has a faster lens (at
>similar zoom settings). TRV20 uses a smaller, slower lens with shorter
>zoom range for the compact size - but it has Carl Zeiss quality.

What ever that is...;-)

>TRV20 has a 1:1.8-2.2 / 4.2 - 42 mm lens
>TRV520 has a 1:1.6-3.3 / 3.7 - 92.5mm lens
>(comparison only valid if both have same size CCD, which is true
>in this case.)

No, it isn't, in terms of active-area for video, and
the difference between f1.6 and f1.8 is minimal at the
short end of the range - and the difference lens speed
is possibly not great at similar angles of view near the long end either...
BTW, I responded to an e-mail from Doggo66@aol.com with
this, regarding the original issues (you may find it useful?):

With analogue systems, the direct-viewed image is recorded
to tape with analogue generation-losses and played back from
tape not only with additional generation losses, but usually
with compensation attempts (with DSP) added (the direct-view
and recorded images are different in both theory and in
observation); with digital camcorders, the image you see is
the same digital image (without generation losses, except
for drop-outs) that will be recorded/played to/from tape,
using the same A->/D->A converters for both (the image seen
is identical to the one recorded, except for tape droupouts,
both in theory and in observation).
As for the original question, I would look to differences
in viewing screens and differences in set-ups with the
camcorders (progressive-scan mode or slow-shutter mode on
one, not the other, etc.), or in characteristics (sharpening
and contrast set-ups on the particular camcorders, chip
differences, etc.).

>All things being equal, faster lens (larger aperture opening) means
>better low light capability.

True. But minor f-stop differences are usually irrelevant
(and lens physical size is also irrelevant in terms of
"light gathering" ability...).