What sizes are detectable from 1m using a fairly good cmos camera?
If I have followed the idea so far How to detect a bullet in air using proximity sensors, you want to detect an object, about 2cm in diameter travelling at 10m/s.

The resolution of the camera you linked to falls to 640 (H) x 480 (V) at 120fps. Also it is in MJPEG format, so you might need to check that everything adds up (i.e. there is enough processing power) to handle this on your processing board.

As @Brian Drummond explained, for a 90 degree viewing angle, to a point 1m away, by drawing the two 45 degree triangles (with opposite and adjacent 1m long), we can calculate that the view width is 2m. 

So at 640x480, a pixel is 2000mm /640pixels; roughly 3mm/pixel, or 6.4 pixels for 20mm (2cm) in diameter. I'd imagine that is easy to detect against a plain, still background. 

However, against a background with movement, or moving light (for example the flashing of indoor lighting, which is imperceptible to the human eye, but may be very significant to that camera) it may be much harder.

Also, if the projectile is moving directly towards the camera, it will move about \$10m^{-s} / 120f^{-s} = 0.08m\$ closer.
So its size will change about 8% (0.08m nearer across 1m starting distance), or change from 6.4 pixels to about 6.9 pixels. 

That sort of change may be swamped by the change in indoor light intensity. So, you might recognise something is there, but it might take several frames to figure out whether it is coming closer, or going away.

IMHO, it would be significantly easier to detect a projectile passing across the camera. The most extreme case would be the camera plane and the projectile are parallel, and the projectile will be in different parts of the image on each frame. From this you could derive speed and direction. 

Try to design a system where the key information is easy to recover from the sensor data.

Hence, I'd be tempted to use more than one camera to give a reasonable view area, and move them away from the target so that the projectile travels across the image plane of each camera, rather than directly at the image plane. My goal would be to make image processing as simple as a binary image 'diff' between successive frames. That 'diff' would provide much more information than a view directly at a projectile.

Edit:
Are you at college or school? If you are, it may be worth checking to see if they have a Raspberry-Pi, or Raspberry-Pi 2, with a camera (quite a lot of UK schools and colleges bought that sort of equipment). That might be enough for you to do some initial experiments, and derive some real data quite quickly. Further, it might cost no money, and there is a lot of R-Pi enthusiasts who may be able to help when things don't go according to plan. Then, you may soon have a much more 'evidence-based' way to make progress.