Both operate at f/4 – both deliver the same light energy during the exposure. Same is true if the lens focal length 1000mm focal length with a working diameter of 250mm. As a example, it the lens has a focal length of 100mm and a working diameter of 25mm, then the focal ratio is 100 ÷ 25 = 4 written as f/4. Ratio to the rescue: We divide the focal length by the working diameter to obtain the focal ratio. In other words, image brightness is intertwined with working diameter and focal length. The greater the focal length, the dimmer will be the image projected by the lens. The greater the working diameter of the lens, the greater is its light gathering power. Now the lens mimics a funnel in that it gathers light. The f-number system aids photographers enabling them to adjust their cameras so that the exposing light energy delivers an optimal exposure. If one is using a half-stop scale, two stops from f/1.189 is f/2.378, which we express as f/2.4. ![]() Since most of us these days use one-third stop aperture scales, two stops from f/1.26 is f/2.52, which we express as f/2.5. f/1.26 is two-thirds of the way between f/1 and f/√2 (f/1.4). F/1.189 is exactly halfway between F/1 and f/√2 (which we refer to as f/1.4). But f/1.2 is really either f/1.189 when using a half-stop scale or f/1.26 when using a one-third stop scale. ¹ Technically, a Micro Four-Thirds lens with an exact aperture of f/1.2 would be equivalent to an f/2.4 lens when used on a FF camera. There is no such thing as full equivalency between different photographic formats. In terms of the resulting depth of field the 25mm f/1.2 Micro Four-Thirds lens is equivalent to a 50mm f/2.5 (2-stop difference)¹ lens used on a full frame camera if the camera-subject distance used is the same and the results from both cameras are viewed at the same display size. In terms of exposure a 25mm f/1.2 Micro Four-Thirds lens is equivalent to a 50mm f/1.2 lens used on a full frame camera. However, modern lens coatings reduce this loss to a small factor, easily negligible in still photo cameras.įor example, is a 25mm 1.2 MFT lens equivalent to a 50mm 1.2 FF lens or to a 50mm 2.0 FF lens? This is complicated slightly in that each glass-air surface in the lens has slight transmission losses, which is greater in lenses with more glass elements. ![]() So regardless of the "size of the lens" (diameter or focal length), the same computed f/stop number represents the same exposure. We might imagine that to be a lens difference, but it is only a sensor difference.Įxposure does "vary" with lens focal length, therefore the whole idea of inventing f/stop numbering is that f/stop does not vary.į/stop = focal length / aperture diameter.Ī lens twice longer has an aperture of twice diameter, for same f/stop number, and same exposure. HOWEVER, the field of view that the cropped sensor can see and capture is seriously affected in the smaller sensor. The lens remains totally unaffected by the sensor. Nor does focal length vary with sensor size. No, f/stop does not vary with sensor size.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |