The Dictionary Of Photography

A True Historic Record Of The Art & Practice Of Photography 100 Years Ago.

Home | About | Photography | Contact






Fishes
Fixed Focus
remove the unaltered bichromate and such portions of the film as remain soluble; after which it is dried. When dry the plate is heated so strongly as almost to char - or at any rate to darken - the film, which then forms an admirable resist to an etching fluid. Perchloride of iron is generally employed, and for details see under the heading Photogravure. For informa-tion bearing directly or indirectly on the fish glue process, and the production of printing surfaces see the following articles: - Galvanography, Daguerreotype (etching of), Obernetter's Process, Electrotyping, Woodburytype, Zincography, Asphalt Process, Chemigraphy, Collotype, Prism (revers-ing), Reversed Negatives, Types (originating by Photographic means), and Filigrane.
Fishes, Photographing. See Animals, Photographing.
Fixed Focus. - This term has become so general of late that one writer actually says, "With regard to fixed-focus lenses I am quite ignorant of the principle on which they are constructed, but it seems to me a most extraordinary thing, if they can be constructed at all, why any other kind should be made. With the lens on my . . . everything from three feet to the extreme distance is in the sharpest possible focus; and this being so, it is most amazing that makers should go on manufacturing lenses that require re-focussing for every picture, which is in all cases an unmitigated nuisance and, in the case of instantaneous pictures, the cause of the loss of more than half the chances offered, and of half the pictures actually taken being out of focus." It is quite possible that there are many in the same state of amaze-ment as the above writer, who may, for all we know, still be in the same state; therefore to him and to others like him it may be of interest to learn that every lens has a fixed focus, and that there is no lens which is manufactured which is not quite as much a fixed-focus lens as the particular lens which called forth the above remarks, and that, moreover, there never has been a fixed-focus lens yet made and never will be. But what we mean to state is this - a fixed focus is a theoretical impossibility, but with every lens there is a point beyond which objects are in sufficient sharpness to satisfy our requirements as to definition, because when the image of a point is less than
318