Basic questions about CCTV cameras

[lionzden 0]

Basic newby questions:

 

If you have a 12mm camera pointed at an area over 20m away and someone steps into the line of the camera only 4m from the camera, will the camera give a good shot of that person?

 

would the shot of that person be better the closer they are to the camera?

[MaxIcon 0]

Short answer: Probably OK at 4m, but likely to get blurry as they get closer.

 

Long answer: It depends on the lens' depth of field and where it's focused. Most cams come from the factory focused for distance rather than close-up, so at a certain point, getting closer results in less focus. You'd have to test it to be sure.

 

Getting good focus everywhere depends on the lens having a small aperture, which reduces low light performance. Most M12 lenses are not very big aperture already, but there's a trade-off between focus depth of field and letting more light through.

 

Long lenses, like 12mm, are more prone to focus issues than short lenses like 2.8mm or 4mm.

[Joeinamillion 0]

Long lenses, like 12mm, are more prone to focus issues than short lenses like 2.8mm or 4mm.

 

What would you say is the closest point for a 2.8mm lens?

[joseph.chen0312 0]

more prone to focus issue than 2.8mm, it sounds weird. Yes 12mm lens will capture more clear than 10, 8, 6, 4, 3.6, 2.8mm. But FOV is more narrow than those wider angle lens. In my experience, 8 or 10mm is enough to catch clean object's profile.

[SyconsciousAu 0]

I use an online depth of field calculator to get some rough figures for my camera's/lenses

 

 

http://www.dofmaster.com/dofjs.html

 

I work on the assumption that fixed lenses are focused on the hyper focal distance and have the maximium F-stop as described in their specs..

 

For a 12mm lens on a 1/3 sensor at F2.0 the near distance is 3.28m so your subject would be in focus.

[mkkoskin 0]

IPVM released a Camera Calculator a while back, handy tool:

http://ipvm.com/calculator