Urnst Loc: Brownsville, Texas

Fast prime and zoom lenses are huge, heavy, and expensive. What with autofocus and high ISOs with digital cameras why is such value put on having a fast lens? Slower can be just as sharp, albeit with a little less bokeh.

cameraf4 Loc: Delaware

Not so much value as cost. It is more difficult, ergo costlier, to make faster lenses.

rmalarz Loc: Tempe, Arizona

For the same reasons as have always existed. Sure one can use a slower lens but that requires using a higher ISO which produces more grain.
--Bob

wjones8637 Loc: Burleson, TX

Fast lenses provide a large lens opening giving a shallow depth of field allowing a subject to be isolated.

Bill

CHG_CANON Loc: the Windy City

If people envy your gear, that's worth something, isn't it?

Urnst Loc: Brownsville, Texas

Thanks for your thoughtful replies. Does moving up just a couple of ISO notches really affect the grain that much? Does a stop or two less in aperture affect separation that much? I wonder. Not in my experience. And I can buy a bag full of slightly slower lenses for the price of one fast zoom and with less weight still carry that bag around. Just my thoughts.

Urnst Loc: Brownsville, Texas

nope

CHG_CANON Loc: the Windy City

Given you have all the answers, why are you asking the questions?

reverand

Digital is so good at higher ISO's, that I think the advantages of fast lenses pretty much disappear, especially if you're talking about telephoto lenses, which are heavy to begin with, and really heavy if they're fast. I'm getting good results at ISO 1600 and even ISO 3200. There's increased noise, but it's barely detectable (I can't tell, looking at 14 x 21 prints which ones are shot at ISO 200 and which at ISO 3200!). And actually, the noise is nothing like what you'd get in increased grain by pushing Tri-X to 1600.

(I'm using a Nikon D850, which, with a 45.7 Mpx sensor, helps considerably at higher ISO's)

amfoto1 Loc: San Jose, Calif. USA

Yes, a large aperture lens can allow you to use faster shutter speed and/or lower ISO, potentially improving image quality...

But I'd argue it's as much or more about being able to use shallow depth of field effects that make large aperture (i.e., "fast") lenses valuable and worthwhile to photographers.

burkphoto Loc: High Point, NC

> better bokeh, if important for your style of work
> less noise due to use of a lower ISO in low light
> less need for auxiliary lighting
> usually better build quality (pro grade vs amateur grade)

Faster lenses are useful for stopping indoor sports action. An f/2.8 lens used at f/4 is usually sharper than an f/4 lens used wide open.

Faster lenses are useful in still life situations for the same reason image stabilization features are useful... You can use a longer shutter speed, hand-held, or lower ISO a bit. But for that matter, image stabilization schemes can allow the use of lighter, smaller maximum aperture lenses in some situations.

There is a "holy trinity of zoom lenses" used by most professionals. In full frame equivalents, they are 14-24mm f/2.8, 24-70mm f/2.8, and 70-200mm f/2.8. Along with that trio is a selection of faster primes, usually between f/1.2 and f/1.8 maximum aperture, and usually 24mm, 28mm, 35mm, 50mm, 85mm, and 100mm or 105mm in length. Some folks, though, will use f/4 versions of the 70-200 zoom, because the f/2.8 version is too freaking heavy!

Most of the variable aperture "kit lens" zooms starting around f/3.5 wide open at their shorter ends are not attractive to working pros. We want speed, image stabilizers, and optical quality not usually found at those low price points.

Urnst Loc: Brownsville, Texas

Ever heard of the Socratic method of teaching and learning? Google it sometime!

selmslie Loc: Fernandina Beach, FL, USA

A fast lens at f/8 is the same as a slow lens at the same aperture when it comes to exposure and ISO setting. But at the same aperture a fast lens might be easier to focus in low light.

On the other hand, some faster lenses are not as sharp as other lenses from the same company that are a stop or two slower. And the slower lens is probably less expensive.

robertjerl Loc: Corona, California

If it moves you need a high shutter speed. Faster lenses allow higher SS in any given light conditions.
And if you shoot in dim light the faster lens becomes even more important and it doesn't matter if your subject moves or not, you still need a faster lens. Upping the ISO only goes so far before the Image Quality goes down.

CHG_CANON Loc: the Windy City

I'll take gear envy from others over cost savings every day of the week, and twice on Sundays.