Focussing Light Amplification by Stimulated Emission of Radiation energy
The Light Amplification by Stimulated Emission of Radiation organisation that exposes the plate inwards a CtP organisation has an touching on the consistency of the halftone dots that brand upwards the picture on the plate as well as thus the consistency as well as integrity of the lastly presswork. The to a greater extent than good focussed, as well as hence sharper, the beam of exposing loose energy the to a greater extent than consistent the resulting halftones volition be.
The 4 principal ways that Light Amplification by Stimulated Emission of Radiation loose energy is focussed on a CtP device inwards gild from basic to most sophisticated:
1) Depth of field. This is the method most oft seen used inwards internal drum CtP machines as well as celluloid imagesetters. It is similar inwards concept to how depth of champaign industrial plant inwards a camera. Although a lens tin give the sack exactly focus at entirely 1 distance, the decrease inwards sharpness is gradual on each side of the focused distance, so that inside the depth of field, the unsharpness is imperceptible nether normal conditions. Typically requires constant calibration to hold imaging consistency.
2) Hard focus. The Light Amplification by Stimulated Emission of Radiation is focussed for the item plate when the CtP organisation is initially laid up. This method is non able to get out alongside issues of variations inwards plate media thickness or equally plate surface to exposure focus quest changes. Hot spots and/or banding may appear.
3) Auto focus. The Light Amplification by Stimulated Emission of Radiation does an auto-focus for the item plate each fourth dimension just earlier actual imaging begins. This method is non able to get out alongside issues of variations inwards plate media thickness or equally the plate surface to exposure focus quest changes. Hot spots may appear.
4) Dynamic car focus. The Light Amplification by Stimulated Emission of Radiation continuously adjusts focus for the item plate during actual imaging. This method is able to get out alongside issues of variations inwards plate media thickness or equally the plate surface to exposure focus quest changes. Hot spots are unlikely.
The "tape test"
To become an persuasion equally to how good the focussing organisation is on a item CtP device, only brand a large "X" using Scotch tape/Sellotape on the dorsum of the plate. Image a 50% halftone covert across the entire plate. Remove the record as well as procedure the plate.
If, subsequently processing the plate, the record is visible inwards the 50% apartment musical note spell so you lot know that whatever variations inwards plate thickness, or plate surface to exposure focus point, that is equal or greater than the thickness of the Scotch tape/Sellotape volition lawsuit inwards variation inwards halftone covert tones as well as thus presswork. It's unlikely that inwards twenty-four hr current to twenty-four hr current production that you'd stick record to the dorsum of a plate earlier exposing it, all the same it is quite possible for a small-scale slice of debris to province on the CtP drum or dorsum of the plate during pre-exposure handling.
Ideally, the imaging integrity of the best organisation would non live compromised past times the record on the dorsum of the plate as well as all you lot volition encounter is a large apartment 50% musical note - no visible "X" pattern.
During the CtP manufacturing procedure the geometric accuracy of the CtP drum on which the plates volition eventually live mounted as well as imaged is measured.
Geometric compenstion
Imagine a grid wrapped just about the CtP's imaging drum.
In a perfect earth the grid would convey perfect integrity.
In reality - the drums are never perfect cylinders.
For those CtP devices that convey this capability, geometric correction distorts the bitmap that volition live imaged on the plate inwards gild to compensate for differences inwards the geometry of the imaging drum on the CtP device. Geometric correction equally good provides CtP device to CtP device integrity so that the plates from different machines volition live equally identical equally possible.
Thermal compensation
Aluminum plates expand as well as contract alongside temperature alter equally much equally celluloid does - virtually 0.5mm across a 1m plate (typical 8-page size) for every 5°C (9°F) temperature change.
That 5°C alter inwards temperature volition lawsuit inwards a one-half row of dots @ 175 lpi misregistration plate to plate which tin give the sack lawsuit inwards the demand for the store to reimage all 4 plates inwards a procedure project fifty-fifty if entirely 1 is truly needed.
Plate imaged twice at different temperatures. Without temperature compensation, the alter inwards plate size due to the ambient temperature alter results inwards a misregistration of the image.
Thermal compensation, for those devices that convey this capability, corrects for ambient temperature variations past times scaling the bitmap inwards such a agency that it is equally if the plates were e'er imaged at a unmarried temperature.
The Light Amplification by Stimulated Emission of Radiation organisation that exposes the plate inwards a CtP organisation has an touching on the consistency of the halftone dots that brand upwards the picture on the plate as well as thus the consistency as well as integrity of the lastly presswork. The to a greater extent than good focussed, as well as hence sharper, the beam of exposing loose energy the to a greater extent than consistent the resulting halftones volition be.
The 4 principal ways that Light Amplification by Stimulated Emission of Radiation loose energy is focussed on a CtP device inwards gild from basic to most sophisticated:
1) Depth of field. This is the method most oft seen used inwards internal drum CtP machines as well as celluloid imagesetters. It is similar inwards concept to how depth of champaign industrial plant inwards a camera. Although a lens tin give the sack exactly focus at entirely 1 distance, the decrease inwards sharpness is gradual on each side of the focused distance, so that inside the depth of field, the unsharpness is imperceptible nether normal conditions. Typically requires constant calibration to hold imaging consistency.
2) Hard focus. The Light Amplification by Stimulated Emission of Radiation is focussed for the item plate when the CtP organisation is initially laid up. This method is non able to get out alongside issues of variations inwards plate media thickness or equally plate surface to exposure focus quest changes. Hot spots and/or banding may appear.
3) Auto focus. The Light Amplification by Stimulated Emission of Radiation does an auto-focus for the item plate each fourth dimension just earlier actual imaging begins. This method is non able to get out alongside issues of variations inwards plate media thickness or equally the plate surface to exposure focus quest changes. Hot spots may appear.
4) Dynamic car focus. The Light Amplification by Stimulated Emission of Radiation continuously adjusts focus for the item plate during actual imaging. This method is able to get out alongside issues of variations inwards plate media thickness or equally the plate surface to exposure focus quest changes. Hot spots are unlikely.
The "tape test"
To become an persuasion equally to how good the focussing organisation is on a item CtP device, only brand a large "X" using Scotch tape/Sellotape on the dorsum of the plate. Image a 50% halftone covert across the entire plate. Remove the record as well as procedure the plate.
If, subsequently processing the plate, the record is visible inwards the 50% apartment musical note spell so you lot know that whatever variations inwards plate thickness, or plate surface to exposure focus point, that is equal or greater than the thickness of the Scotch tape/Sellotape volition lawsuit inwards variation inwards halftone covert tones as well as thus presswork. It's unlikely that inwards twenty-four hr current to twenty-four hr current production that you'd stick record to the dorsum of a plate earlier exposing it, all the same it is quite possible for a small-scale slice of debris to province on the CtP drum or dorsum of the plate during pre-exposure handling.Ideally, the imaging integrity of the best organisation would non live compromised past times the record on the dorsum of the plate as well as all you lot volition encounter is a large apartment 50% musical note - no visible "X" pattern.
Geometric compenstion
Imagine a grid wrapped just about the CtP's imaging drum.
In a perfect earth the grid would convey perfect integrity.
In reality - the drums are never perfect cylinders.
For those CtP devices that convey this capability, geometric correction distorts the bitmap that volition live imaged on the plate inwards gild to compensate for differences inwards the geometry of the imaging drum on the CtP device. Geometric correction equally good provides CtP device to CtP device integrity so that the plates from different machines volition live equally identical equally possible.
Thermal compensation
Aluminum plates expand as well as contract alongside temperature alter equally much equally celluloid does - virtually 0.5mm across a 1m plate (typical 8-page size) for every 5°C (9°F) temperature change.
That 5°C alter inwards temperature volition lawsuit inwards a one-half row of dots @ 175 lpi misregistration plate to plate which tin give the sack lawsuit inwards the demand for the store to reimage all 4 plates inwards a procedure project fifty-fifty if entirely 1 is truly needed.
Thermal compensation, for those devices that convey this capability, corrects for ambient temperature variations past times scaling the bitmap inwards such a agency that it is equally if the plates were e'er imaged at a unmarried temperature.
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