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Time delay and integrationtdi

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>"Pulling focus" is self-evident. When the term came into use can only be >answered by someone a lot older than I am. BTW, where's Jeff Kreines? Billy Mitchell ("Intolerance" etc) used lenses where the barrel was 'pushed' and 'pulled' to affect focus. As he eminently was not able to pull at the lens and crank the camera simultaneously, he was (probably) the first cameraman to yell "pull focus" to his assistant. As is explained in one of the links at : http://www.xs4all.nl/~wichm/filmsize.html If you can't find your info there, it most probably does not exist : Robert Rouveroy csc The Hague, Holland I plan to live forever. So far, so good.

Time delay and integrationmeaning

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TDI camera principle

Time-delay integration (TDI), also known as drift scanning, is a mode of reading out a charge-coupled device (CCD) camera that allows a continuous image or scan of the sky to be recorded. Normally, most astronomers use CCDs in the point-and-shoot or stare mode. A telescope is pointed to a particular position of interest on the sky and made to track at that position. A shutter is opened to expose the CCD, and then closed while the electronic exposure recorded by the CCD is read out. In drift-scan mode, the telescope is parked, tracking is turned off, and the camera shutter is held open. As the sky drifts across the field, the electronic exposure recorded by the CCD is shifted across the pixel array, row by row, to match the drift rate of the sky. The time it takes a source in the field to drift across the whole array is the exposure time of the scan. Since the readout is continuous, this is the most time-efficient way to survey large areas of sky. There is no pause between exposures to wait for the readout of the camera. The largest-area photometric surveys to date have been made with drift-scanning cameras. Smaller-scale surveys have used drift scans for astrometry of faint standards, suitable for the re-calibration of the relatively imprecise positions of the large photometric and Schmidt-plate catalogs.

>"A cause of intense anguish" -- how appropriate!" I heard a rumour that the early Bausch and Lomb anamorphic lenses had two focus knobs on them, requiring two focus pullers. If a shot was buzzed each assistant always had someone to point at. Lots of intense anguish there, I'm sure. Art Adams, DP Mountain View, California - "Silicon Valley" http://www.artadams.net/

Time delay and integrationin ccd

"Rack focus" does indeed derive from the gears used, as in rack and pinion. The pinion is usually a smaller gear and the rack is usually a straight assembly or rack of teeth as in a view camera and some early MP cameras-- not to be confused with medieval torture device of the same name, although as has already been pointed out, there are similarities in effect for the focus puller. "Pulling focus" is self-evident. When the term came into use can only be answered by someone a lot older than I am. BTW, where's Jeff Kreines? Brian Heller

Integration timevs exposuretime

Charge-coupled device cameras were first used in drift-scan mode on ground-based telescopes beginning in the 1980s with the CCD Transit Instrument (McGraw et al. 1980) and the Spacewatch Telescope (Gehrels et al. 1986). These early instruments consisted of CCDs with field sizes of ∼10 arcmin, capable of covering 10–20 square degrees in a single scan. The Spacewatch camera was the first to use a CCD for automated detection of near-Earth asteroids (Rabinowitz 1991). The CCD Transit Instrument had two CCDs aligned east–west allowing simultaneous scans of the same field in two different passbands. Advancements in computer speed and capacity have since allowed the construction of much larger scanning cameras made up of CCD mosaics.

>I heard a rumour that the early Bausch and Lomb anamorphic lenses >had two focus knobs on them, requiring two focus pullers. If a shot was >buzzed each assistant always had someone to point at. Nothing to do with anguish. Old Mitchell’s, B&H's, Auricons and the like had a side viewfinder: one could only "see" focus and composition if the lend was 'racked over'. It was moved over with a big knob and it rode on a notched horizontal track. Hence: rack for focus or in short 'rack focus'. Some camera's had a view tube that was 'racked over' to look through the negative that thereby acted like a ground glass. That was before the black backing coat of course. Robert Rouveroy csc The Hague, Holland I plan to live forever. So far, so good.

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I've been interested in the origins of the term "rack focus", guessing that it derived from the gears used in a follow-focus system. Probably first used as a noun, later becoming an action. I decided to look up the word "rack", and one of the definitions is : "A cause of intense anguish" -- how appropriate! Can anyone confirm the above origin of the term? And where did "pull focus, or focus pull" come from? Chris Mosio Cinematographer/Seattle

Robert Rouveroy writes: >Nothing to do with anguish. Old Mitchell’s, B&H's, Auricons and the like >had a side viewfinder: one could only "see" focus and composition if the >lend was 'racked over'. Not to quibble with so eminent a film historian, but I believe the term "rack focus" pre-dates rack-over cameras, but I may be wrong. However "The Rack", the medieval torture instrument, and gear rack derive from the same source. "The Rack" used a rack and pinion system for mechanical advantage. Brian "ouch" Heller I 600 DP

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