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        Q: What is a fresnel lens?
A: By combining of two lens= & gt ; The Power became double= & gt ; focal length becomes one-half  The Fresnel lens reduction the quantity of material required compared with a traditional spherical lens by splitting the lens into a set of concentric annular sections otherwise known as `` Fresnel zonings '' , which are theoretically unlimited . [ six ]   In the firstly ( and enormousst ) variants of the lens , each regions were in fact a separated prism . Though a Fresnel lens might appear like a only piece of glass , closer exam has revealed that it is numerous little slices . 'Single-piece ' Fresnel lenses was subsequently produced , be utilised for auto headlights , braking , parking , and turn signal lenses , and therefore on . In modern-day times , computer-controlled milling equipment ( CNC ) maybe it is employed to manufacture most complicated lenses .   In each of these zonings , the general thickness of the lens 's reduced , effectively splitting the constant surface of a standards lens into a set of surfacing of the same curvature , with stepwise discontinuithe relationship between them . In fact a Fresnel lens is feasible to are considered as an array of prisms organizing in a circular fashion , with steeper prisms on the edges and a approximately flat convex centre .   Fresnel lens designing enabling a significant reduced in thickness ( and thus mass and volume of material ) , at the cost of reduction the imaging quality of the lens well , that 's why specific imagery apps such as photograph still use traditional bulky ( non-Fresnel ) lenses .   Fresnel lenses is a general made of glass or plastic ; their sized varies from huge ( old historical lightstations , meter sized ) to medium ( book-read aids , OHP viewgraph projectors ) to little ( TLR/SLR camera screens , micro-optics ) . In numerous instances these people are very thin and flat , nearly flexible , with thicknesses in the 1 to 5 millimetre range . 

Q: Lens trouble with my Canon. Help?
A: If you do n't comprehend what this meant that , you 're NOT ready to go shop .  You 've no idea what you want/requirements and will presumably regret your purchases . Please do a little more learn before you part with your money .   Here 's a good starting :    What do all the letters mean on a lens ?   Let 's pick apart the nomenclature in the 55-250 is full name :   EF-S 55-250mm f/4-5.6 IS   The EF-S relates to the fact that it 's made for APS-C ( 1.6-crop ) cameras , and were not able to utilise on cameras with a 35mm `` full frame '' sensor .   The 55-200mm relates to the range of focal lengths accessible   The f/4-5.6 mean that the wideest accessible aperture setting is f/4 at the wideer angle end , and f/5.6 at the telephoto be stopped . The smaller the aperture values , the more light gets in , counter-intuitively .   For reference , f/4-5.6 are regarded as a `` sluggish '' lens and the majority consumer zooms declined into this category . A `` quick '' zooming will have f/2.8 as a broadst aperture , and this will be continuous throughout the zooming range . An f/2.8 lens will congregate twice as many lighting as an f/4 lens , and 4 times as much as an f/5.6 lens . Fast zooms are greatr , heavier , and *much* more expensive .   With respect to IS ( Nikon calls this VR ) it 's a very useful for longer focal lengths , in particular when you 're using a sluggish lens , because your shutter speeding will be slower . Do bear in mind that IS does not halt subject motion , so it is no good for shots of moving subjects where blurring is generated by too slow a shutter speeding to stop the subject . For people , that are usually approximately 1/50 2nd , but a lot quicker if these people are moving swiftly , such as during a sporting event .   The above is a direct quote of a DPC member called `` Kirbic '' . 

Q: Is there a substitute for a fresnel lens?
A: see link below Share to :