When does a lens get "fast"

[timmyquest]

At what point do you consider a lens "fast"

[HJMinard]

It depends on the focal length, to some degree ... and, of course, it's all relative. In general, however, I'd say apertures larger than f4.

[Rokkorfan]

The poll is flawed - it should read: $700, $1000, $3000, $5000

Cheers,

Antony

[CyberDyneSystems]

Both Jay and Antony are absolutely correct.

One aperture does not set the standard,. and thus a much better indicator of a fast lens really would be price related.

f/4 is fast for a midrange telephoto,. and it's really fast for a long telephoto...

But it's dog slow for a 50mm. Or even a short telelphoto like 85mm or 135mm

Heck even f/5.6 is fast for an 800mm....

[timmyquest]

Both Jay and Antony are absolutely correct.

One aperture does not set the standard,. and thus a much better indicator of a fast lens really would be price related.

f/4 is fast for a midrange telephoto,. and it's really fast for a long telephoto...

But it's dog slow for a 50mm. Or even a short telelphoto like 85mm or 135mm

Heck even f/5.6 is fast for an 800mm....


Yeah i understand that logic and it crossed my mind to an extent. :cry:

[Wazza]

I call fast, f0. Apparently my 17-40L (f4), wasn't clicked on 100%. And after 20 shots, before I chimped, I wondered why all the shots were WELL underexposed. It had actually done f0, and 1/8000 shutter speed (maximum) on all the shots. :D

Now that was FAST.

[MarkH]

For a zoom f5.6 is just the standard - definately not fast. F4 is faster than standard by one stop, but not really fast. F2.8 is the fast zoom and it is when the higher precision AF kicks in on Canon EOS bodies that have the option.

For Primes it seems to come down to whats normal on the focal length. For a 300 I would say f2.8 is very fast. For a 400 I would rate f2.8 EXTREMELY fast. But my 50 f1.8, though fast is very cheap, the f1.4 is very fast and not too badly priced.

Anyway, I chose f2.8 because I usually use zooms.

[CyberDyneSystems]

Nice observation on the zoom side of thing Mark,. that certainly evens the playing field a lot more to consider zooms,. as the variation is a lot less than with the primes as far as "what is fast?"

[pcasciola]

I chose 2.8 as well because that seems to be the fastest for the zooms out there as well as the larger primes like Mark said, but why is that? Is there some reason Canon cannot make a f/2.0 zoom?

[CyberDyneSystems]

Faster means larger,. larger means more glass = more expensive.
As we see with primes like 85mm f1.8 and 85mm f1.2... sometimes what seems like just a slight speed advantage on paper (using numbers) means a huge increase in lens size, weight and of course cost.

Anyone seen a 50mm f/1 next to a 1.8??? The difference in size is actually funny! :)

Look at 200mm f/1.8 next to a 200mm f/2.8...
again.. it's positively frightening how big the size difference is!!!!

Of course faster lenses can be made,. and in fact they are,. but not for portable camera use.

Interesting that of you look at the focal length to f/stop ratio.... the fastest zoom lenses made are made by Sigma ;)

[ssim]

Canon cannot make a f/2.0 zoom

I wouldn't be surprised if they don't already have the technology to do this. I would surmise that it is a matter of cost and how well a zoom would sell at an exhorbinant cost.

Can you imagine the 100-400 at f2.0.

[John Trogdon]

Just like a woman. . . . . when it becomes expensive.

[pcasciola]

Interesting that of you look at the focal length to f/stop ratio.... the fastest zoom lenses made are made by Sigma ;)You know, I never really thought about it before, but you're absolutely right. That Sigma 120-300 f/2.8 caught my eye recently. Canon doesn't have anything close to that at that speed. And of course there's the 300-800 f/5.6 from Sigma as well.

I'd be happy with a 70-200 f/2. That would be the ultimate indoor sports zoom.

[CyberDyneSystems]

Yep,. the fastest 300mm Zoom is that Sigma f/2.8,.. and the second fastest 300mm Zoom is Sigma's 100-300mm f/4 EX :)

I have ... certain types of... dreams...:rolleyes: ... about the 300-800mm f/5.6! :shock:

[tim]

I've decided F2.8 is the slowest lens i'll buy in "standard" length lenses. I might have to go F4 for a zoom lens because I can't justify an F2.8 given how much i'd use it, but for all other lenses i'll be aiming for F2 or faster.

[ssim]

I have ... certain types of... dreams...http://www.photography-on-the.net/forum/images/smilies/icon_rolleyes.gif ...

That's probably waaay too much information. This is a family board you know.

Your post prompted me to actually go and look at this 300-800 lens. It looks like a monster.

[timmyquest]

Your post prompted me to actually go and look at this 300-800 lens. It looks like a monster.

Indeed it is, and its performance is suprisingly pretty darn good.

Check this thread out

http://hardforum.com/showthread.php?t=861207

[AdamG]

Indeed it is, and its performance is suprisingly pretty darn good.

Check this thread out

http://hardforum.com/showthread.php?t=861207

I checked out that link. What's that little thing at the small end of the lens? Oh yeah, must be a Nikon camera. Man, that's a large lens!!! If I owned that, well...., I'd feel quite adequate, of course. :D

[picture-this]

When it rolls down a steep hill.

[Rokkorfan]

OK, here in summary, is my idea of when a lens is fast.

Primes:

Under 20mm f/2.8
20mm f/2.0
24mm f/2 or lower
28mm f/1.8 or lower
35mm f/1.8 or lower
50mm f/1.4 or lower
85mm f/1.4 or lower
135mm f/2 or lower
200mm f/2.8 (Medium fast, really should be f/2 or lower)
300mm f/2.8
400mm f/2.8
500mm f/4
600mm f/4
Anything longer f/5.6

Zooms:

Any focal length between 16mm and 200mm f/2.8
Telezoom from 100-300/400mm f/4
Anything longer than 400mm f/5.6

In reality, the only way to see significantly faster lenses that are practical is with lenses designed for smaller sensor sizes.

Cheers,

Antony