Subscriber Discussion

Lens Limitations

I'd like to know the reason for degraded low light performance with very short lenses, as stated in the paragraph below.

I was under the assumption that short focal lenght was not an obtacle for low light situations.

"Degraded low light performance: Very long lenses (as well as very short ones) typically capture significantly less light than normal lenses in the 3mm to 10mm range."

Good question. I've moved this from the IPVMU forum to the main members one.

If it's really short but wide, then it will be fine (recall that higher f stops come from narrower or longer lenses). However, in surveillance, super short lens are typically narrow as well.

For instance, fisheye lenses. It's hard to find a fisheye lens that is less than f/2.0. Similar, Thiea's super wide angle lenses are f/1.8. By contrast, 3mm HD lenses are commonly f/1.2, allowing far more light to pass.

The issue is that optical designs/formulae have nonlinear variables that become dominant at focal length extremes. It is still reasonably acheivable to have a _balanced_ design in a 3mm lens at f/1.0 to f/1.2 maximum aperture/iris. Keeping that same speed at half the focal length (1.5mm) requires one to two more orders of magnitude of glass, cost, labor, size, and the production lens would likely have significant optical performance shortcomings in some areas. It is much easier to produce a balanced design at the extremes with a slower maximum aperture/iris (numerically larger). Thus the quote above about degraded light performance. But we are talking about VERY short lenses here (greater than about 100 degrees hfov on a 1/3" imager).