## Can sliding apertures on zooms die and stay dead please page 2 photo.net photography forums k electric jobs 2015

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As you know, the camera lens functions much like a funnel in that it gathers light based on its working diameter (aperture). That’s the good news! The bad news is — As you zoom in, light energy playing on film or digital sensor is abridged. In other words, as you zoom to higher and higher focal length, you pay the price of reduced exposing light energy. nyc electricity cost The amount of light loss due to increasing focal length is considerable. 4 other gases in the atmosphere Doubling the focal length from 50mm to 100mm results in a 4X loss. Zoom from 50mm to 200mm; the consequences are an 8 fold loss in light energy at the focal plane. In other words, the light energy arriving at the film or sensor intertwines working diameter with focal length. This is a phenomenon of physics that can’t be avoided, however it can be tamed.

Opticians tame this light loss via the f-number system. gas pains or contractions The f-number assignment is derived by dividing the focal length by the working diameter. The result is a ratio called the “focal ratio” (f-number for short). Thus the f-number assigned to a 50mm with a working diameter of 25mm is 50 ÷ 25 = 2 (written as f/2). 1 unit electricity cost in tamilnadu Zoom to 100mm and the math is 100 ÷ 25 = 4 (written as f/4). Zoom to 200mm and the math is 200 ÷ 25 =8 (written as f/8). This is the basis for the unavoidable light loss with the zoom.

As I said above, the light loss is unavoidable. This is true, but we can find work-arounds. Suppose you make the lens larger in diameter and then mechanically link the working diameter of the aperture of the iris to the zoom mechanism. gas leak One could evade the light loss this way. Sounds good, but likely impractical — thus too complicated and too expensive.

Alas – how to avoid the devastating light loss? Opticians must use multiple lens elements to mitigate the seven foremost lens aberrations that plague us. This can be accomplished by constructing the lens using a minimum of seven individual lens elements. gastric sleeve scars To handle the light loss of the zoom, the front lens group is fashioned to magnify the iris. In other words, the diameter of the iris appears larger or smaller than reality with the zoom. Thus the outside world sees a varying aperture diameter. This actually works! The degree of magnification changes with the zoom, and this action results in a constant f-number throughout the zoom.

Vivitar did NOT advertise this as a zoom lens, as the focus point does change quite dramatically as the lens is zoomed. None the less, it’s one of the few f/2.8 variable focal length lenses available for the FD system, and covers three useful focal lengths(35mm, 50mm, 85mm). On the few occasions I dared do weddings, I usually cut my second shooter loose with that lens on my T70 along with a roll of Portra 400NC and a Canon 299T during the reception.

I know it pales in comparison to modern offerings, but it was quite well regarded in the 1980s and still brought decent money(esp. for a 3rd party FD mount lens) in the mid-2000s when I bought mine. For that matter, now that I’m a full blown Nikon guy I’ve wanted to pick an N/AI mount one, but the few that I’v watched or even nibbled on have brought more than I wanted to pay(and not too far off from what an older 35-70 f/2.8D AF-Nikkor would cost). Most of the Series 1 Vivitars were universally well regarded in their day, and although they’re not as well built as the best manual focus Nikkors or Canon L lenses, they’re a definite cut above the build quality of Sigma ARTs. electricity in india ppt Even in their day, they were a BIG step up in build quality from Nikon Series E lenses and the "consumer’ oriented Canons.