1 - Is there a typical distance you can read a number plate.
2 - Would I then be able to read a number plape at say 25m.
3 - What would the picture be like at night with IR on, or are they
just too grainy
4 - Or are my problems only due to the PC capture card.



Q1 Agreed with Andy above you need at least 8 pixels per character.

Q2 To be pedantic:

* A 1/3" sensor has a size of 4.6 x 3.8mm

* Using an 8mm lens the field of view at 25000mm will be:

* (25000/8) * 4.6 = 14375mm wide

* Sensor has 752 horizontal pixels.

* 14375/752 = 19mm per pixel. you really need 5mm per pixel.

So answer is "no way". A lens of 25mm or longer will assist.

Q3 Day/Night cameras mechanically remove an internal IR filter for night
operation, hence become sensitive to IR, hence increased gain. Spatial
resolution will be comparable with day

Is the vehicle going to be in motion? If so how fast?

You need to think about the shutter speed, over which you may have no
control. 30mph =~ 13 metres per second so vehicle will move 13cm in 1
millisecond.

Another issue is that of interlacing. This camera will use an interlaced
(so called "interline transfer") sensor. The even lines and odd lines
(called fields) are read out alternately at the rate of 50 fields per
second. The fields are in fact exposed 20 milliseconds apart, with nasty
consequences for resolution.

It is complex but if there is motion the camera will have potentially half
the vertical resolution as horizontal.

++++++++++++++

I'm not sure exactly what you are wanting to achieve (permanent
installation?) but I would be inclined to look for some kind of HDV
camcorder - preferably CCD rather than CMOS - as a starting point.

david