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The alternative to the ultra-fast long telephoto?
On Thursday, June 14, 2018 at 2:28:51 AM UTC-4, RichA wrote:
Now with cameras and their exceptional high ISO capability, these slower but high-quality telephotos are now good and perhaps, preferable. https://www.dpreview.com/news/7758816413/nikon-developing-compact-and-lightweight-500mm-f5-6-lens The option has been around for "long enough", but one of the ways that the OEMs has functionally obstructed it is through their dSLR specifications. Specifically, when Autofocus capability is disabled when a certain f/stop value is exceeded. If memory serves, the common "upper limit" value had been f/5.6, with some exceptions at f/8 (such as offered only on higher end bodies, and/or only at the center focus point). From a designer policy standpoint, what's needed to really enable this is (enabled by said higher ISO sensitivity) is for the camera to be designed & allowed to (try to) AF at f/8, f/11 and/or even f/16. For example, if we use lens filter diameters as a convenient surrogate, a 200mm f2.8, a 300mm f/4 and a 400mm f/5.6 all have primary apertures of 77mm, whereas when we increment up by one stop (eg, a 300mm f/2.8, 400mm f/4, or 500mm f/5.6) the aperture area needs to double, which is ~120mm. Conversely, if we 'speed up' the dSLR's Autofocus system to allow for an even slower lens, a 500mm f/8 should drop to be only 77mm. -hh |
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