Q-see QNC-7001b or Dahua 1.3mp camera lens change.

[mwhitnell 0]

Hi,

I have been reading some about changing lens, especially on this mini bullet camera I have. It has a 6mm lens...I would like a 3.6mm lens. The fitting is M12. I notice some posts mentioning IR corrected, and IR cut filters. Most lens I see on ebay or wherever, do mention an IR lens, but never do they mention IR corrected. I guess what I am asking: Where do you get a IR corrected fixed 3.6mm lens? And if you don't, is it really that far out of focus day VS night? Does the IR cut filter change any of the focus plane day vs night? by moving the IR plane closer to the daylight plane?

[MaxIcon 0]

Usually, if they specify IR, it means IR corrected, but some lenses block it instead. The description sometimes makes that clear, but not always, and either have to contact the vendor or take a chance. Some of my board cam lenses are marked MPIR.

 

IR focuses at a different focal length than white light in a non-corrected lens, so the IR image is blurry if the daylight image is sharp. How much is dependent on the lens and aperture, but my Arecont 5MPs are very blurry when using IR with a non-IR compensated lens and a wide-open aperture.

 

The IR compensation is done in the manufacture of the lens, similar to how they get rid of chromatic aberration, and can't be fixed with a filter or coating. A moving sensor would do it, but I don't know of any cctv cams that use this. Autofocus would probably work, for the cams that use it, but I don't have any experience there.

 

When the filter moves, it just blocks or unblocks the IR. If the filter's out and IR is unblocked, you'd have good focus with white light, but the colors would be off due to the extra IR.

 

Here's a page that demonstrates the difference in focus. If you look down at the pics of Legos, you'll see the with/without compensation comparison.

 

http://www.infraredphoto.eu/Site/GentleIntro2.html