Focusing Panoramic Cameras

By Ethan Ace, Published May 05, 2013, 12:00am EDT (Info+)

Focusing panoramic cameras is really important. Indeed, after testing 9 different panoramic cameras across many manufacturers, we believe this must be done manually for each camera. This might seem unnecessary as panoramic cameras are, after all, fixed focal lenses. However, though all the cameras in our tests shipped focused by the factory (with the exception of ImmerVision, sold as an accessory), we found it necessary to refocus nearly every one to maximize image quality.

Since panoramic cameras have lower pixel density by nature, due to their wide FOV, fine focus issues may be difficult to spot. Worse, because of the FOV, even being slightly out of focus will have a large negative impact on image quality. For these reasons, we recommend users always refocus panoramic cameras. 

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Comments (3)

Hi Ethan,

Great write up. If you could wave a magic wand and make the process easier to set up and configure, what would it be?

In general, how could panoramic cameras be improved to make it easier and more painless for the installer? They all seem to more similar than different from one another in this respect.

Cheers,

Ian

Ian, my question is why panoramic cameras, given their fixed focal lenses, even allow for focusing adjustment. I presume this issue is that the distance of the imager to lens varies among different cameras and the off the shelf lens needs to accommodate different distances?

Since the lenses in panoramic (minidomes) can't be changed anyway, why even allow for focus adjustment?

I assume the other alternative would be to add in ABF but that I imagine would increase cost and probably size as well.

Hi John,

Ideally the lens is set by the factory to what is called its “hyperfocal” distance. At this focus point, everything forward of that line is perfectly in focus. The bigger the F-Stop of a lens, the bigger this hyperfocal range is. Taken to an extreme, a pinhole camera for example has everything perfectly in focus in front of the ‘lens’ as well as perfectly in focus behind the lens. It doesn’t matter where the subject is infront, nor does it matter (for focus) where the film or sensor is behind.

This is also the same principal that allow ‘point and shoots’ to work that have no ability to adjust focus. The focus range is usually 4’ to infinity, but they either need flashes to work indoors, or bright sunlight outdoors.

The challenge that security manufacturers typically have is balancing the need for low light performance versus depth of field. Pinhole cameras have their exposures measured in minutes versus milliseconds, making them of course unsuitable for these types of applications. Typical lenses in panoramic applications have relatively low F-stops - in the 1’s (1.0, 1.4 or 1.6) - which decreases depth of field, making manual focus adjustments a requirement.

Complicating matters, the distance to the subjects across the entire field of view has a rather big range. With a panoramic camera mounted in the middle of a room for example, the distance to the floor in the middle is much shorter than the distance to the objects at the perimeter of the view. Your suggestion of focusing for the edges is a good one for all the reasons you mentioned. If low light performance wasn’t as critical a priority, a lens with a higher F-Stop could be used to get everything in view tack sharp across the entire view.

Since many customers use this in a relatively well lit retail setting, it would be interesting to know whether this would be an acceptable trade off. (low light versus sharpness and no-adjustment to focus required). This would (I think) be a good application for P-Iris and might be cheaper than doing a back focus adjustment to tweak the focus.

Speaking of lenses and back focus, another point of frustration for manufacturers is the back focus range for various brands of lenses vary quite a bit. So called, board mount “prime” lenses or fixed mm lenses used in these types of cameras are easier to work with since they usually screw into a 14mm or 19mm mount. The factory or installer can simply twist the lens to move it in or out to adjust the focus point.

Where manufactures really get into a bind is with C/CS mount lenses that clamp down to a fixed back focus distance. The two choices that we have is to allow for a bit of slop on the verifocal range (the extremes might not be able to focus quite perfectly) or we have to incorporate a relatively expensive back focus adjustment mechanism. Most manufacturers today simple fix the back focus best we can and rely on the fact that most installers use verifocal lenses that can adjust for the variability.

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