Why do older camera lenses have faster F-stops?

Started Apr 14, 2013 | Discussions thread
MisterBG
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Re: Why do older camera lenses have faster F-stops?
In reply to EinsteinsGhost, Apr 15, 2013

SergioNevermind touched on the reasons for faster F-stops in his post.

On manual focus SLR's you relied on a "split image" or later a "microprism" focussing aid in the viewfinder. These needed plenty of light to function. I recall manufacturer warnings that smaller aperture telephoto lenses (F4 or less) would tend to cause half of the split image focussing screen to black out. This was especially true when using a teleconvertor with a longer focus lens, when split image viewfinders became useless.
The secondary reason was because film speeds were much lower in those days, which meant larger apertures were needed. Average speeds were ASA (ISO) 100 or lower, and 400 ASA was about as fast as you could get with easily available films. With pushed processing you could uprate Black and White 400 to 800 ASA or a little more, but at the expense of an increase in contrast.

Modern autofocus does not rely on having a bright image, so manufacturers can make lenses with a smaller maximum aperture, which are consequently cheaper to produce.

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