Report zooms in on giant camera resolution test charts throughout the US










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Dozens of two-dimentional aerial photo calibration targets are scattered all across the United States, according to a report by the Center for Land Use Interpretation. Constructed mostly during the 1950s and 1960s, these large outdoor charts were used as ‘a platform to test, calibrate, and focus aerial cameras traveling at different speeds and altitudes.’ The report points out that although some of these ‘charts’ are still used for some optical camera testing and calibration, they are primarily relics of the past.

GoogleEarth image of a tri-bar array at Eglin Air Force Base, Florida.

According to the report, ‘the 1951 Resolution Test Chart on which [these outdoor calibration symbols are] based is more than 60 years old and was designed for film cameras, and predates high-resolution digital systems and CCDs. The arrangement and spacing of the lines is not well suited for computer analysis (it’s not a continuous single row, but two or three rows of pairs), and it has other frequency and modulation issues that make determining sharpness by digital means inaccurate.’

This ground-level photograph shows one of the giant calibration targets as it appears today, at Cuddeback lake in the Mojave desert.  [photo: CLUI]

The report mentions some targets specifically, for example, ‘three Tri-bar targets remaining at Cuddeback Lake are visual analog relics of the aerial viewing revolution, and they may be the only ones on public land. With dendritic cracks filling with brush, breaking through the uniformity of the 5:1 bars (each bar and space between the bars is five times as long as it is wide), the flat surfaces are peeling, crumbling and sprouting, producing dimensionality, and relief.’

(via Petapixel).







Comments


huyzer

Wow, very neat.


wilerty

Interesting. The paint on those targets is not from the 50s or 60s, so somebody must be using them …


mauijohn

There are two of them in the desert. about 4 miles west along the side of that road.


bizi clop

These patterns still could be used to calibrate or compare Google/Bing Maps.


Tan68

interesting snippet, though.
like something from damninteresting.com


Tan68

Nothing explains the guys leaning out while someone holds their belt so they can look straight down from the Empire State building. It is all frenzy, wrapped in absurdity, inside a compulsion.


mike kobal

this finally explains the long lines of photographers with cameras around their necks patiently waiting to get to the top of the Empire State building, so many cross walks and patterns, perfect for focus calibration!

Source Article from http://www.dpreview.com/news/2013/02/18/Giant-camera-resolution-test-charts-around-the-US

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