Question about "fast" and "slow" lenses

I've come to understand that both my lenses are "slow" lenses, because of the f#. First question, is it indeed determined by the f#? Second question, what is considered a "fast" lens...for instance, something that would be good to use in lower light weddings/receptions. I doubt I'll get into wedding photography full-time or anything, but would love to learn as much as I can. What would thrill me to no end is finding a local photog who needs "help," lol.

TIA for your comments.

A 'fast' lens is one with a lower f-stop. Id say anything f2.8 or lower could be considered a 'fast' lens.

The lower F stops allow for "faster" shutter for a given situation. Anything under F4 I consider fast. F4 seems to be bottom for the average. So ones lower are considered fast.

If you have an f/2.8 lens, you can generally shoot indoors but you have to set ISO to 1600 or 3200, and sometimes you'll only have shutter speeds on the order of 1/20 or so. At that high of an ISO, you'll have to use noise ninja or neat image to remove the noise, but you will also lose some detail. F/2.8 is fast enough for stage performances and the like.

To really shoot indoors without flash you need a lens that has an f/1.4 to f/1.8 aperture (1.4 being prefereable). I personally just use bounced and diffused flash indoors, because the light is more predictable.

Oh, and just for clarity:
f/4 allows twice the shutter speed over f/5.6
f/2.8 allows twice the shutter speed over f/4
f/2 allows twice the shutter speed over f/2.8

So, if your f/5.6 lens only gets a shutter speed of 1/4, then an f/2 lens would yield a shutter speed of 1/30.

Fast = F/2.8, F/2, F/1.8, F/1.4, F/1.2, F/1.0

Slow = F/3.5, F/4, F/5.6, & Above

Primes & Zooms 2.8 & Faster are classified as fast glass.

Thank you all. That makes a lot more sense now. Much appreciated!!!

Actually, I'd differentiate this way:

Zooms: f/2.8 is fast. f/4 is average, anything else is slow.

Primes: Wide-angle to short telephoto, except 50mm: f/2 and faster is fast, anything else is average or slow.

50mm: f/1.4 is fast, f/1.8 is average, f/2 and slower is slow:

200mm: f/2.8 and faster is fast

300mm+: f/4 and faster is fast.

Agree with Jman, generally as you get out into telephoto territory, the "rules" change a bit. I wouldn't call a 500mm f/4 "slow", I'd call it "freakin' huge"

Jman13 wrote in post #5981516
Actually, I'd differentiate this way:

Zooms: f/2.8 is fast. f/4 is average, anything else is slow.

Primes: Wide-angle to short telephoto, except 50mm: f/2 and faster is fast, anything else is average or slow.

50mm: f/1.4 is fast, f/1.8 is average, f/2 and slower is slow:

200mm: f/2.8 and faster is fast

300mm+: f/4 and faster is fast.

I agree.

I'd like to add 2 categories:
UWA Primes and Zooms (21 mm or less on FF, 13 mm on APS-C): F/2.8 and faster is fast, F/3.5-F/4 is average, anything else is slow.
Fisheyes (15-16 mm FF, 10 mm and less on APS-C): F/2.8 and faster is fast, F/3.5 is average, anything else is slow.

Kind regards, Wim

The criteria change as you can see...but what's made the biggest diff is that we can now get results with ISO 1600 that with film we were getting at ISO 400...and the higher ISO the "faster" the film...the more light sensitive, the faster the grain became sensitized by the incoming light...
...so now with ISO 1600 we can now get results with F:2.8 that we were getting with F1.4 at ISO 400 (two F:stops 400 vs 1600, difference)...that makes 2.8 seem 'fast' to many us oldies....to whom the results of shooting F2 or wider @ today's 1600 seem unreal...but much appreciated...

Why are we talking about "fast" lenses or "fast glass"? The word fast relates to speed,
In this context that means the shutter, which is in the camera not the lens.
So why not confine the terminology for lenses to f numbers then there no dispute.
Davol

Because 'fast' is easier to say than 'large aperture' and everyone in the photography world knows what you mean.

wow, maybe we should get a sticky on this, or insert an entry on this in the FAQ sticky thread.

f 1.8 is easy to say and is a definitive number. I still ( as an engineer) can not see the the point in using a subjective term when there is a clear quantitative scale available.
Davol