Electrical transmission or interconnection systems – Switching systems – Switch actuation
Patent
1983-06-23
1985-06-18
Hix, L. T.
Electrical transmission or interconnection systems
Switching systems
Switch actuation
355 69, H01H 4300
Patent
active
045242909
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a time switch.
A time switch according to the present invention may be used for controlling any desired apparatus but is particularly, though not exclusively, useful for producing photographic prints. The switch may be used in the production of colour prints from negatives or diapositives, but it has particular advantages in the production of monchrome prints, and the following description of the invention will accordingly be largely confined to that field of use.
Time switches for controlling operation of an apparatus, for example illumination from a photographic enlarger, for a single preselected time period are of course very well known.
In the production of monochrome prints, it is often desired to render some region of the image denser or less dense than other regions and this is accomplished by over- or under-exposing those image regions by comparison with a base exposure time.
Accordingly time switches have been proposed with a programmable memory which are arranged to interrupt an exposure run after a succession of previously entered times so that after the shortest of those times, appropriate regions of the photosensitive print material can be shaded so that they are not further exposed. Such switches present considerable advantages over a single period timer, but they are not wholly satisfactory for two main reasons. Firstly, each time period requires separate estimation or calculation and entry, and secondly, if it is desired to reproduce a print using a different base exposure running time, then all the other time periods again require individual calculation and entry.
It is an object of the present invention to provide a time switch especially suitable for photographic purposes in which these disadvantages are alleviated.
According to the present invention there is provided a time switch characterised in that it comprises: timer means and means for starting the timer means; input and memory means for entering and storing a base running time; a plurality of further input means each associated with logic and memory means for entering a multiplier and calculating and storing the particular multiple of said base running time; means for successively stopping the timer means at the expiration of each stored multiple of the base running time, and at the end of the base running time; timer controlled switch means; display means for displaying the entered base running time, and, during a run, the elapsed running time.
A time switch according to this invention has the advantage that only one time period, the base exposure running time, need be entered as such. Other time periods are simply entered as desired as multiples of that base running time. This is of very considerable practical convenience. The invention has the further advantage when used for photographic enlargement that if it is desired to reproduce the tonal quality of a print using a different base running time, for example in a print of different image size, then all that is necessary to alter is the base running time. The same multiples of the base running time will give the same tonal balance to the prints made.
In the most preferred embodiments of the invention, said multipliers are powers of 2. In other words, said logic and memory means are arranged for the calculation and storage of running times which are f/stop number multiples of the base running time. A doubling or halving of the base exposure running time is an increase or decrease respectively of 1 f/stop. It is a fact that photographers and photographic printers are accustomed to thinking of exposure time variations in terms of f/stops and those experienced in that art are familiar with the difference in print density which will be the result of a variation in exposure of a given number of f/stops, that is, the result of multiplying the exposure time by a given power of 2.
The interval between successive multipliers is preferably at most 2 raised to the power 1/2, that is to say, the square root of 2. This allows finer control of exposure running time
REFERENCES:
patent: 3611159 (1971-10-01), Florsheim, Jr. et al.
patent: 3832054 (1974-07-01), Sable
patent: 4035661 (1977-07-01), Carlson
Electronique Industrielle, No. 10, Feb. 15, 1981, (Canterbury, GB), P.I.; "Timer pour Chambre Noire", pp. 43-44.
Hix L. T,.
Rutledge Della J.
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