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1, JVC BN-VF815 Camcorder Battery constant aperture lens and fixed iris lens is different, the former refers to a zoom lens, the zoom process, its maximum aperture, or set the aperture and the current remain the same lens, which means that only a lens aperture size, which kinds of lenses are common in the past, but now almost impossible see. Heritage ah.

2, constant aperture lens, a common principle is that the location of the camera lens aperture film began, to the lens bottom of the last lens, the location of all the lens when the lens zoom, and focal plane distance remain constant. The general non-constant aperture lens, the position of the aperture when the zoom will be running around  JVC BN-VF714 Camcorder Battery

But not all such lenses, the second principle is that a typical 4 4 zoom lens, the first film and the fourth lenses to form a convex lens in the normal sense, or a fixed focus lens, while at a concave lens is inserted between two lenses to change the virtual image distance in order to achieve the zoom, but the zoom will affect many things, so adding the fourth lenses, this move will lead to 2,3-lens aperture size and inclination of their For, as they affect the communication of light caliber.

So when moving the lens, aperture also changed.

3, aperture = aperture / focal length, but this is not absolutely correct. In addition, not the lens aperture diameter, the front of the lens mount diameter, or caliber, but a virtual, what does not exist, it is the above mentioned 2,3 months in a typical 4 4 zoom in zoom in charge of the two to achieve an opening angle between the concave lens, the inclination of the lens when the zoom will change.

In addition, the focal length is not correct to say, in fact, should be the image distance, not focal length ...jvc bn v408u battery

4, for a 135 SLR camera, if a shorter focal length, such as 20mm, so manufacturers have to adopt counter-telescope structure *, so that although the equivalent focal length is 28mm, but may actually be more than 70mm.

Do not you see, MA 20/2.8 aperture is only f2.8, but the diameter to 72mm, than the MA 100mm/f2.8 caliber (55mm) are big!

5, the macro lens macro trip into port, you will find the exposure combination is inconsistent with the theoretical aperture combination, especially when the zoom ratio of more than 0.5! Because at this time is much larger than the focal length of the image distance. So do not really think that the aperture size = aperture / focal length.

6, a number of lenses with a double-grating structure, such as the Minolta 135 STF and the 28-70G, the second grating will also affect the iris. 28-70G have exaggerated the first caliber, the fox that the second optical grating it may affect the pass, specifically do not know, because Fox had not seen again in addition to which it is a double-grating lens.

* Minolta and Nike have not adopted the structure of anti-ultra-wide-angle telephoto lens, but the bottom will hit the reflector, so when in use must be pre-rise to use such a reflector lens, similar to the paraxial camera. But at this time can not SLR viewfinder, you need to install a seat next to the flash axis of the viewfinder ... The metamorphosis is designed to be existed.JVC BN-V107U Camcorder Battery