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FORUMS Canon Cameras, Lenses & Accessories Canon EF and EF-S Lenses 
Thread started 13 Jul 2005 (Wednesday) 14:19
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What makes a fast lens a fast lens?

 
Candi ­ lynn
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Jul 14, 2005 14:41 |  #16

le




  
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condyk
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Jul 14, 2005 14:42 as a reply to  @ Candi lynn's post |  #17

Candi lynn wrote:
le

Ah, you speak French .... :lol: :lol:


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DavidEB
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Jul 14, 2005 14:56 |  #18

a fast lens is one that goes home with you on the first date.


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CyberDyneSystems
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Jul 14, 2005 15:29 |  #19

As mentioned.. "fast" refers to the shutter speeds the lens allows due to the lens having a larger aperture.

In many cases indeed faster or larger apertures may not be required or desired..

But the opposite is certainly true as well,. it all depends on your shooting style.. and it takes more glass and more money to get that larger faster aperture.

As it is simply a matter of physics and economics that a "fast" lens in certain focal lengths will require it to be expensive.. usually one can in fact equate fast and expensive lenses with lenses of higher quality.

As for trying to put a given f/stop # as a indication of whether a lens is "fast" or not.. it can't be done.

As just like the f/stop # in general.. what constitutes a fast f/stop and what does not is completely dependant on/and relative to the focal length.

f/2.8 is NOT that fast for a 50mm... nor is that large of an opening...

But f/4 is EXTREMELY fast for a 600m... and it's a much larger opening.

:)


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Citizensmith
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Jul 14, 2005 17:19 |  #20

get some duct tape and a Ferrari. Attach lens to car, accelerate. Very fast.

CDS makes an excellent point, fast really depends on focal length. However, as lenses get wider it can also matter a bit less whether or not the lens is fast as the wide lens lets you use slower shutter speeds anyway. If you want to keep that shiny new 600mm steady you need every ounce of light possible. If you are using a 20mm you can get away with a lot more.


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CorruptedPhotographer
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Jul 15, 2005 03:45 as a reply to  @ CyberDyneSystems's post |  #21

CyberDyneSystems wrote:
f/2.8 is NOT that fast for a 50mm... nor is that large of an opening...

But f/4 is EXTREMELY fast for a 600m... and it's a much larger opening.

:)

is it not :

50mm / f2.8 = 17.85

600mm / f4 = 150

Where 17.85 and 150 refer to the size of the opening @ those apertures and speeds?

If true, then the 150 is 8 times (150/17.85) more open or wider than the 17.85.


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Devil
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Jul 15, 2005 17:41 |  #22

I've never used an addon lens to an SLR before so just wanted to have something clarified.

In cases like the 50mm 1.8 or the 75-300mm f4.5, does this mean that I cannot choose to take photos in 50mm f8/f32 or 300mm at f2.8/f32 etc ? Does this mean that if I place one of these lenses on the DSLR it'll override and limit the available modes on the camera ?

Am I correct in assuming this ?


  
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SkipD
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Jul 15, 2005 19:03 as a reply to  @ Devil's post |  #23

Devil wrote:
In cases like the 50mm 1.8 or the 75-300mm f4.5, does this mean that I cannot choose to take photos in 50mm f8/f32 or 300mm at f2.8/f32 etc ? Does this mean that if I place one of these lenses on the DSLR it'll override and limit the available modes on the camera ?

When a lens is advertised as, for example, 50mm f1.4, the only thing that tells you is that the maximum aperture (minimum f-stop number) for that lens if f1.4. Almost all SLR lenses can be "stopped down" to smaller aperture settings - some manually, and some automatically. Typically, lenses can be stopped down to f16, f22, and sometimes more. You have to look at the more complete specs for any particular lens, not just its "name".

Hope this helps decode the info for you....


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JulianL
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Jul 15, 2005 19:19 as a reply to  @ post 653800 |  #24

ayotnoms wrote:
Huh?
The FD mount lens that came with my Canon-AE1 25 years ago was an F/1.8

I'm fairly certain that fast lenses in the sub-f/2.8 range have been around for long time and f/4 was as slow then as it is now--for some circumstances, of course.

discuss amongst yourselves.... :-D :-D

Yep, I have a Rollei 50mm f/1.8 lens that is probably close to 30 years old.


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stuntman
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May 09, 2011 13:36 |  #25

the bigger the hole, the faster the lens -




  
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DAMphyne
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May 09, 2011 13:51 |  #26

JulianL wrote in post #658253 (external link)
Yep, I have a Rollei 50mm f/1.8 lens that is probably close to 30 years old.

I had a Rokkor 58mm 1.2 lens in the mid 70's, and I'm sure it's not the earliest or fastest of it's time.
A fast lens has simply a larger lens opening.
The camera focuses and meters with the lens wide open, thus a larger lens opening should allow faster focus in the auto focus cameras. I will say that a "Faster" lens was much easier to manual focus, consequently, it was faster.


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wrxrocks
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May 09, 2011 14:41 |  #27

Don't learn about fast L lenses. They will cost a lot of $$$$. On a serious notes, fast referes to the speed of the shutter. Any lens will be slow if used in a dark room without flash. Similarly, any lens will be fast if used outside in the middle of a sunny day.


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SkipD
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May 09, 2011 15:14 |  #28

stuntman wrote in post #12376767 (external link)
the bigger the hole, the faster the lens -

Do you realize that you just reopened a thread that died nearly six years ago? I have not seen most of the forum members who had posted in this thread in MANY moons. Thus, your answer will essentially go on deaf ears. :rolleyes:


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OhLook
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Dec 27, 2012 19:48 |  #29

SkipD wrote in post #12377504 (external link)
Do you realize that you just reopened a thread that died nearly six years ago? I have not seen most of the forum members who had posted in this thread in MANY moons. Thus, your answer will essentially go on deaf ears. :rolleyes:

Noooo . . . The thread was linked at the bottom of the page where I had asked the same question. I read it.

EDIT: Hey, is SkipD still around?


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AmosTFairchild
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Dec 27, 2012 20:34 |  #30

Mmmm. Zombie thread. Just keeps on walkin.




  
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What makes a fast lens a fast lens?
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