A Major Flaw in Long Lenses and PTZs Found

The best I can tell this has been going on for years. It is something we have seen but never formally tested / proved.

This major quality degradation has been masked by offering longer lens length. Of course, longer lens lengths with degraded resolution is a poor tradeoff, as you are forced to take a narrower FoV to get the details one desires.

I am not sure what, if any, manufacturers will do. Our understanding is that size and cost constraints restrict options. Its certainly possible to build long length varifocal lens without such problems, but, at least today, these issues appear to be the norm.

However, we are planning to modify the lens calculator to factor / display the risks involved with contemporary long length lenses.

"For the stadium, we used a 5-megapixel camera at 75-feet wide and 34 pixels per foot (ppf). Then we opened up to a higher resolution: 10-megapixels at 110-feet wide at 33ppf. We tried a 25-135mm lens that performed great with the camera and became one of the lenses they ultimately used in the installation. After seeing several different scenarios, they picked a target of 40ppf for every seat in the stadium." Quote Link

Similar setups are getting popular with NFL stadiums.

Isn't some of the quality degradation explained by motion blur, which is intensified as you zoom? Could be due to unseen vibrations, e.g. due to nearby machinery/natural harmonics of the pole, etc. I would try putting your finger on the camera enclosure and check if it has any impact on the directionality or intensity of the blur.

Does the test hold true for PTZ at standard definition at these high focal lengths? I recall reading several years ago that the glass in the lens of most high pixel cameras don't support anywhere near the pixel densities of these compact cameras. There has to be good reason a digital SLR camera has a lens that is 10x the length and width of a lens used in a typical HD security camera.

The important point is not the size of the sensor and the focal length of the lens, you have to think about the angular size of the pixel as it maps onto your targets. So it's the ratio of these two quantities that is important. Lenses are all about bending light and angles. The lense has no idea what sort of sensor you're going to put behind it. But really, I think the problem here is not the lense at all. It is the atmosphere--see my previous note about anisoplanaticism. The angular sizes of the pixels in this test are getting pretty small and are of a size at which atmospheric interference warps and blurs the image. You always run into this if you make the magnification large enough, but it happens sooner if you are looking out over a hot desert, for example, where there is lots of atmospheric trubulence because of the rising columns of air. I think you can see in the movie that this is starting to happen in these test. Again, see my previous note.

Howdy Ethan! Do y'all have a link for any additional images/detail that go with this test?

Howdy everyone!

It's now been over a week since I asked about any other image data on this test. First off as you can see above, John didn't say there wasn't any, but instead just asked me for exactly what I was lookin for. I obliged him generally, and then a little later I screen printed exactly what I seen in the search results to make me curious. By the next mornin the search no longer returned that result. Gone just like that, without a word to Adam. I still have my screen prints though, and this here is what I can reconstruct of what looks to be a different version of this here 'Major Flaw' report, (but this one talks about an extra fuji lens, to prove where the fault lie):

Long Focal Length PPF Test

We tested two megapixel rated lenses from Fujifilm [[part numbers]] As well as two HD PTZ cameras to see how image quality holds up under these long focal lengths.

Using the 8-80mm at its longest focal length, visible quality was equivalent to images of 50% or lower PPF. [[100' 190 vs 80, 94 vs 45 etc. Additionally depth of field was limited. Focused on our subject at ~500, images were blurry around 250-300'. [[FOV example]]

To see if this was a function of long focal length or the lens itself we tested another lens, a Fujinon ___ 4-12mm megapixel rated lens, set to ~8mm, the same field of view as its 8-80mm counterpart. At this focal length, the 4-12mm lens is demonstrably better, providing approximately the PPF levels it should (X at Y distance)

So was this written before the test or after?

If after, where are those 'demonstrably better images' which prove the lens is at fault? I'm having a hard time thinking of any answers that don't involve either:

Writing the report before even doing the test and / or

Ignoring important but not helpful results to reach a foregone conclusion

Though the reason I can't think of an explanation might just be my own lack of imagination, so make-up your own mind! But based on the reception given to my earlier question and the removal of the search data, I'm not expecting an answer.

Now that I've done said my peace, I will saddle-up and get out of y'alls hair.

The poor MTF at longer lens lengths is most likely source of the image quality issues.

Yes, it may very well be.

The 3MP fuji lens is listed at f/1.4 at 8mm, and although I can't find a published spec for it at 80mm, a conservative guess puts it at around at least f/3, possibly a good deal more.

Where the snb-5004's 1/3" image sensor looks to have a pixel width of ~3.5 microns

• A lens at f/2.8 corresponds to an airy disk of ~3.7 microns.
• A lens at f/4.0 corresponds to an airy disk of ~5.3 microns.
• A lens at f/5.6 corresponds to an airy disk of ~7.5 microns.
• A lens at f/8.0 corresponds to an airy disk of ~10.7 microns.

Note that severe diffractive effects aren't seen until typically the airy disk width is 2x the pixel width, although some distortion is noticeable at greater than 1x. So depending on what the effective f-number of the lens actually is, the sensor/lens combination may be indeed diffraction limited.

On the other hand it's hard to be sure because, at lower f-numbers the difference is small. One idea would be to retest the lens with a sensor with a higher resolution and smaller pixel width. Maybe try the SNB-6004 or even the 3 MegaByteMegaPixel 7004, as they may be easier set similarly, being in the same Wisenet III family.

If the image is merely resolution-limited then going to the higher resolution sensor should yield a substantial improvement. If the image is severely diffraction limited though the improvement should be minimal.

Thoughts/corrections?