Clayton's Sticky - A Glossary Of Terms.

[Bob Hart]

GROUNDGLASS BASED IMAGE RELAY.


GLOSSARY OF TERMS AND DEFINITIONS.

ACHROMAT. - An easyspeak shortform of the words "achromatic dioptre", which define a lens made of two glass elements designed to eliminate chromatic abberations (rainbow effect) in lens arrangements.

In groundglass based image relay, the achromatic dioptre is often used as a close-up attachment to a camera lens to enable focus on a groundlass located too close for the lens on the camera to be able to realise sharp focus.

AGUS35. A name coined early by a reader-contributor to posts in the original thread published by Agus Casse, who made the first alternative groundglassed CD-R disk based home-made image relay device, to attach a definition to the device.

ALDU35. A definition applied to early developments of fixed groundglass devices. (this comment likely needs correction - The first dvinfo publisher of a fixed groundglass alternative home-made adaptor was Alain DULAY, from whose name the acronym was derived.)

AO5. - An abbreviation commonly used by home-builders to define aluminium-oxide abrasive powder of five micron particle size. Sometimes also used to define the grade of the groundglass finish.

BACKFOCUS. - Is commonly a definition of a facility to enable user-friendly in-field re-adjustment or re-collimation of a lens to its correct relationship to the film plane or CCD imager surface.

Most commonly this is found in ENG cameras where vigorous usage might cause a lens and mount to be stressed out of collimation. It is otherwise an arduous task requiring specialist equipment and skills if the function is not built-in.
Backfocus is sometimes used to define "relay focus", when a groundglass device entirely replaces a lens on a ENG style detachable lens camera.

To avoid confusion, the words "relay focus" should be used, as the words "backfocus" are also used to describe adjustment of the relationship between the SLR or objective lens and the groundglass its image falls upon.

BARREL DISTORTION. - An optical defect in a lens system which yields images in which a grid of straight lines is displayed as outward bulging curves towards the image edges. ((+)).

BCX. - An abbreviation which defines a bi-convex single element lens, often used in a relay path to combat brightness falloff in corners of the projected image.

C.A. or CHROMATIC ABBERATION. - This is an optical artifact, an unwanted side effect of refraction by a lens, caused by the separation of the different colours of light.

This is the rainbow effect seen when a beam of pure visible light is shone through a prism. With a camera lens or image relay system, chromatic abberation causes colour fringing on edges of high contrast and blending (muddy colour rendering) of different colours towards the corner extremities of the image.

It is often observed during the early developmental stages of an enthusiasts home made adaptor when single-element close-up lenses are used. Achromatic dioptres and apochromatic dioptres are designed to eliminate this defect or correct it as far as is practically possible.

CONDENSER. - Usually a bi-convex or plano-convex single element lens, often used in a relay path to combat brightness falloff in corners of the projected image. It is almost mandatory in static groundlass systems where larger image area is recovered from the groundglass to diminish in scale, the visible texture of the groundglass below the resolving ability of the camera.

DOUBLET. - Two pieces of glass or other material of similar transparency, formed into lenses and paired together to function as a single lens, sometimes joined at mating surfaces by an adhesive bond. commonly seen in the form of the achromatic dioptre.

ELEMENT.- A single piece of optical glass or other material of similar transparency, formed into a lens.

FALLOFF. - Diminished brightness in corner areas of the groundglass image, caused by the greater angle of incidence of light falling from the lens onto the groundglass towards the edges of the projected image.

This is most often associated with use of a groundglass which is insuffiently opaque, lenses with small aperture, attempts to recover an image from too large a groundglass area or combinations of these causes.

Remedy of this problem is often attempted with success by use of one or more condensors, immediately adjacent the groundglass.

FILM-OF-GRAIN. - A visual artifact which is created by incorrect aperture adjustments or high shutter speeds, mostly associated with elliptoid groundlass motion systems.

FIXED PATTERN. - A visual artifact which is created by incorrect aperture adjustments, high shutter speeds, or both in combination, mostly associated with elliptoid groundlass motion systems and static groundglass systems.

FLICKER. - Visually apparent as a variation of brightness or flicker caused by variations in the opaqueness of the groundglass finish on a disk system (spinner). Is not seen with oscillating/orbital, elliptiod or fixed groundglass systems.

FLIP. - A term which defines rotation of the image viewed by the camera 180 degrees to appear upright.

GHOSTING. - A visual artifact observed when the opacity of a groundglass is not sufficient to prevent pass-through of aerial image to the video camera. It appears most commonly with bright highlights as a sharply defined object within a fuzzy halo.

GROUNDGLASS. - An opaque rear projection screen which displays a lens image to a video camera.

HOTSPOT. - This is an extreme manifestation of FALLOFF. Most often it is associated with use of a groundglass which is insuffiently opaque, lenses with small aperture, attempts to recover an image from too large a groundglass area or combinations of these causes.

Remedy of this problem is often attempted with success by use of one or more condensors, immediately adjacent the groundglass.

IMAGE ERECTION. - Make what you will of it, however in groundglass based image relay speak, an erotic connotation is not intended. - A term which defines rotation of the image viewed by the camera 180 degrees to appear upright or flipping of the image.

This term, used in early posts relating to adaptors, has fallen away in favour of the current definition "FLIP".

MACRO. - A badly used easyspeak derivation of the industry words, "macro-focus", generically used to describe a close-up function built into a general purpose camera lens.

The definition has been furthur corrupted to become "macro-filter" to described an add-on close-up lens which attaches by the filter mount of a camera lens.

NON-COHERENT. - Not a state of drunken inebriation, but wordstuff which defines the two-stage path of image relay, to a displayed motion picture film image or to a displayed groundglass based electronic image.

This term is found in technical literature published by P+S TECHNIK.

OBJECTIVE LENS. - In groundglass based image relay, this term has come to define the lens which is on front of the image relay device.

OSCI. - A shortform term applied to the MINI35-400 groundglass based image relay adaptor to distinguish its oscillating or orbital motion system from the earlier MINI35-300 which is a rotating disk (spinner) system.

PCX. - An abbreviation which defines a plano-convex single element lens, often used in a relay path to combat brightness falloff in corners of the projected image.

PINCUSHION DISTORTION. - An optical defect in a lens system which yields images in which a grid of straight lines is displayed as inward bulging curves towards the image edges. ))+(( .

RUNOUT. - Engineer speak for something running out of correct alignment or centricity, or not running true. Call it a wobble for simplicity sake.

Most often this term will be read in relation to disk systems (spinners) which do not run true to the focal plane and lose sharpness, or develop a phasing focal effect.

SLR LENS. - SLR is an abbreviation of the words "single lens reflex", most commonly applied to camera lenses designed for many popular 35mm still-image cameras.

The focus and field of view offered by the lens to the film plane is also relayed to the camera operator's optical viewfinder by the single lens reflex system.

The acronym TTL (through the lens) is sometimes substituted but is more often associated with automatic metering and exposure control systems of SLR cameras.

In groundglass based image relay, this term has come to define the lens which is on front of the image relay device.

SWIRLING. - A visual artifact which is created by incorrect aperture adjustments, high shutter speeds, or both in combination, mostly associaterd with orbital groundlass motion systems.

VARIABLE DENSITY ARTIFACT. - Visually apparent as a variation of brightness or flicker caused by variations in the opaqueness of the groundglass finish on a disk system (spinner). Is not seen with oscillating/orbital, elliptiod or fixed groundglass systems.

VORTEX. (FROM HELL). - A visual artifact which is created by incorrect aperture adjustments, high shutter speeds, or both in combination, mostly associated with disk (spinner) groundlass motion systems.


---------------------
FOOTNOTE:
---------------------

These definitions are derived from usages which have become customary within a community of home-builders of groundglass based image relay devices.

There may have been some straying from the mainstream meaning.