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FORUMS Canon Cameras, Lenses & Accessories Canon EF and EF-S Lenses 
Thread started 19 Feb 2009 (Thursday) 10:12
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Stupid question about fast lenses...

 
Toeslider
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Feb 19, 2009 10:12 |  #1

I apologize for not finding this answer on my own, as I'm sure it is out there somewhere, but I figured it would be easier just to ask and be done with it.

I understand that a fast lens will let you shoot with a faster shutter speed when wide open, but my question is this:

Let's say I have a 5omm f/1.8 and a 50mm f/1.2. If I set BOTH of them to f/8, will the 1.2 allow me to use a faster shutter speed? The aperture would be the same, but the surface area of the glass would presumably be bigger on the 1.2 lens. Does that make a difference, or are you only gaining something when shooting wide open (or at a bigger aperture than what is available on the 1.8 )?


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Papa ­ Carlo
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Feb 19, 2009 10:19 |  #2
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Toeslider wrote in post #7359518 (external link)
I apologize for not finding this answer on my own, as I'm sure it is out there somewhere, but I figured it would be easier just to ask and be done with it.

I understand that a fast lens will let you shoot with a faster shutter speed when wide open, but my question is this:

Let's say I have a 5omm f/1.8 and a 50mm f/1.2. If I set BOTH of them to f/8, will the 1.2 allow me to use a faster shutter speed? The aperture would be the same, but the surface area of the glass would presumably be bigger on the 1.2 lens. Does that make a difference, or are you only gaining something when shooting wide open (or at a bigger aperture than what is available on the 1.8 )?

Let me rephrase your question. You have two cars Ford Focus and Lamborghini. There is a part of highway where you always expect a cop and so you drive both cars at 65 mph there. So is your lamborgini still a faster car and do you gain anything by owning it ?




  
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justaf ­ IREMAN
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Feb 19, 2009 10:27 |  #3

short answer is no. same aperture, same shutter speed, same iso,doesnt matter what lens. its the universal law.



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past canon gear....XS, 7D, 2 5DII, 2 1DIII, , 18-55IS, 24-70L, 85 F1.8, 85LII, 35F2, 35L, 24L, 200 F2L, 580EXII....

  
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Toeslider
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Feb 19, 2009 10:29 |  #4

Papa Carlo wrote in post #7359559 (external link)
Let me rephrase your question. You have two cars Ford Focus and Lamborghini. There is a part of highway where you always expect a cop and so you drive both cars at 65 mph there. So is your lamborgini still a faster car and do you gain anything by owning it ?

That doesn't really answer my question, but sticking with your analogy:

The Lambo is faster, but I don't need the extra speed and can't afford the price premium. However, if the Lambo became invisible to the police at 80 mph and the Focus didn't, I might consider owning it.

I'm not trying to bash good glass, just wondering if it works any different at F8. The reason I ask is because I noticed that using my 50mm 1.8 outdoors at f8 it was giving me a SS of 400, whereas if I use my 18-55mm kit lens at f8 at 50mm it seems to give me a SS more like 125-250. I know one is a prime and one is a zoom with more elements in it, but I was just wondering how the two primes would stack up against each other at f8. I don't have a fast prime to compare with.


Canon XTi, 18-55mm kit IS and non, 10-22mm, 28mm 2.8, 50mm 1.8, 580EX
Sigma SD14, 18-125mm DG, 20-40mm f/2.8 EX

  
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Toeslider
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Feb 19, 2009 10:30 |  #5

justaf IREMAN wrote in post #7359621 (external link)
short answer is no. same aperture, same shutter speed, same iso,doesnt matter what lens. its the universal law.


That's the answer I was looking for. Thanks.


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gasrocks
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Feb 19, 2009 10:33 |  #6

It is only when you use f/1.2 or f/1.4 (on the 50/1.2 lens) that you gain any "speed." However, the better quality, way more expensive lens, is sharper at f/1.8, and f/2, etc.


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nuffi
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Feb 19, 2009 10:36 |  #7

The short answer is that if you have enough light then you don't get a great deal of difference between the two lenses. The L set to f/8 will require the same shutter speed and ISO setting as the nifty set to f/8.

Actually, I like the car analogy. Kinda sorta. The lambo lets you drive at the same speed as the focus past the speed traps and you get to your destination at the same place, but you do have small, subtle things to look forward to: The boke is typically better with L lenses, as is the IQ. And they have such style....




  
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matonanjin
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Feb 19, 2009 10:40 |  #8

nuffi wrote in post #7359672 (external link)
Actually, I like the car analogy. Kinda sorta. The lambo lets you drive at the same speed as the focus past the speed traps and you get to your destination at the same place, but you do have small, subtle things to look forward to: ....

Small subtle things to look forward to like the Lambo will pick up more women.
:lol:


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Toeslider
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Feb 19, 2009 10:44 |  #9

I would hope the fast glass build quality would be better, and the glass itself is surely better than on a slower lens. I was just wondering if one would help me out further up the scale.

I was just curious because of what I was seeing, but that probably has more to do with shooting through multiple layers of glass in a zoom vs. a few layers in a prime.

Here's a specific problem I'd like to solve. Let's say I am shooting an indoor car show. I want to stay at f8 to get the depth of field I want, but it gives me too slow of a shutter speed and I get blur from the turntable the car is rotating on. Is there any other solution OTHER than increasing the ISO to get the shutter speed up where I want it and retain the depth of field?


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Sigma SD14, 18-125mm DG, 20-40mm f/2.8 EX

  
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GyRob
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Feb 19, 2009 10:59 |  #10

Toeslider wrote in post #7359739 (external link)
I would hope the fast glass build quality would be better, and the glass itself is surely better than on a slower lens. I was just wondering if one would help me out further up the scale.

I was just curious because of what I was seeing, but that probably has more to do with shooting through multiple layers of glass in a zoom vs. a few layers in a prime.

Here's a specific problem I'd like to solve. Let's say I am shooting an indoor car show. I want to stay at f8 to get the depth of field I want, but it gives me too slow of a shutter speed and I get blur from the turntable the car is rotating on. Is there any other solution OTHER than increasing the ISO to get the shutter speed up where I want it and retain the depth of field?

No
Rob
eddit
mm just thought about this regarding DOF if your using say 100mm at f8 to take the shot But then take the same shot at f4 with a 17 mm your DOF would be greater and you gain 2 stops shutter speed .
think im right here :) but happy to be corrected.


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Tumeg
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Feb 19, 2009 11:21 |  #11

To the OP; there is no such thing as a stupid question :) I am sure this thread has, or will, help lots of people.
Anyway, I see where you are coming from, but as already said... The answer would be no.


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runninmann
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Feb 19, 2009 11:29 |  #12

Toeslider wrote in post #7359635 (external link)
That doesn't really answer my question, but sticking with your analogy:

The Lambo is faster, but I don't need the extra speed and can't afford the price premium. However, if the Lambo became invisible to the police at 80 mph and the Focus didn't, I might consider owning it.

I'm not trying to bash good glass, just wondering if it works any different at F8. The reason I ask is because I noticed that using my 50mm 1.8 outdoors at f8 it was giving me a SS of 400, whereas if I use my 18-55mm kit lens at f8 at 50mm it seems to give me a SS more like 125-250. I know one is a prime and one is a zoom with more elements in it, but I was just wondering how the two primes would stack up against each other at f8. I don't have a fast prime to compare with.

Either ISO setting or available lighting was different. That big of a difference shouldn't have anything to do with the lens.


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charlesu
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Feb 19, 2009 11:38 |  #13

matonanjin wrote in post #7359701 (external link)
Small subtle things to look forward to like the Lambo will pick up more women.
:lol:

I disagree. You can probably get 1 woman in. If you crammed them you might get two. However even a relatively small economy car will easily hold 3.


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k_wakasugi
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Feb 19, 2009 11:58 |  #14

charlesu wrote in post #7360108 (external link)
I disagree. You can probably get 1 woman in. If you crammed them you might get two. However even a relatively small economy car will easily hold 3.

lol, this one made my co-workers look at me like i'm crazy. hahah... thanks for the laugh.


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[Hyuni]
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Feb 19, 2009 12:22 |  #15

I had the same question, too
Thanks for answering everyone!

I was debating on getting the 1.4 vs the 1.8 50mm but I think I'll stick with the 1.8 for now at least.


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