Is this true? (Technical question)

[AlphaBjerke]

While shooting the other day, I met a fellow shutterbug who told me that with the higher end lenses--for instance, the Canon L Series--you can shoot at a lower ISO because more light gets through the better glass. (And Mike, if you joined DPS like I suggested, I don't doubt you, but someone else didn't go for what you said so I'm just throwing it out there)

Specifically, he had an expensive lens and I had a kit lens. We were both shooting at the same aperture and the same shutter speed, but he was able to shoot at 200 ISO when I had to shoot at 400 to get the same settings.

What do you folks know about this. It sounds logical to me!

[fletch]

Originally Posted by AlphaBjerke

Specifically, he had an expensive lens and I had a kit lens. We were both shooting at the same aperture and the same shutter speed, but he was able to shoot at 200 ISO when I had to shoot at 400 to get the same settings.

What do you folks know about this. It sounds logical to me!

This isn't true at all. The ISO you shoot at will be related to your shutter speed and aperture. These are equals on any lens. f/4 on your kit lens will give exactly the same exposure as f/4 on his L lens and therefore you should have the same ISO.

Where expensive lenses have an advantage is that the often have larger max apertures (often refered to a fast lenses) than kit lenses. The are often sharper and suffer less from distortion and chromatic aberation etc. So expensive glass is better but it can't magically lower your ISO at an aperture.

[candleman]

Originally Posted by fletch

This isn't true at all.... The ISO you shoot at will be related to your shutter speed and aperture....

Where expensive lenses have an advantage is that the often have larger max apertures (often refered to a fast lenses) than kit lenses. The are often sharper and suffer less from distortion and chromatic aberation etc. So expensive glass is better but it can't magically lower your ISO at an aperture.

exactly,

theres 2 reasons i can think of that caused you to shoot at different iso's..
1. is because i bet he was at a different focal setting than what you were at.

(correct me if i'm wrong)
Aperture is expressed as a fraction of the focal length...
different focal length = different size hole for the same f/# value


2. you were metering for a different part of the image,
you may be exposing for midtones, while he may have been exposing for highlights
~this is very easy to do.. especially if you have different camera bodies, on different metering modes at different focal lengths.
(a wider angle could include more highlights.. or conversley ...more shadows therefore differing exposure)

a comparison of SOOC images "His Vs. Yours" would help allot in determining what the causes were.

[fletch]

Originally Posted by candleman

(correct me if i'm wrong)
Aperture is expressed as a fraction of the focal length...
different focal length = different size hole for the same f/# value

I can't because you are right!

f/s are f/s are f/s though and you will get the same expsoure at f/4 whether you are using a 12mm lens or a 400mm lens. (Exposure as in ammount of light, you will obvioulsy have a different field of view so both photos may not be properly exposed)

[dcclark]

Sounds like you met a fellow who wanted to brag about his equipment. Oh well, I hope your photos turned out just as well, if not better.

[vandergus]

I don't know, I think he's sort of right. He just didn't say it very clearly.

If you're both shooting at the same aperture and same shutter speed, then the same amount (roughly) of light is getting to your sensors. So maybe he was just underexposing his shots by shooting at ISO 200. If he's shooting with an L lens, though, there's a good chance that it has a larger maximum aperture than your kit lens. So, if he wanted, he could shoot at f2.8 when you could only shoot at f4, which, consequently, would allow him to shoot at a lower ISO and achieve the same exposure.

Shooting at the same apertures, though, your exposures should be pretty close.

[jprime84]

One missing variable is what cameras you guys were using.

[Jim Bryant]

Interesting question, if you had two lenses and one was a f/4 and one was a f/2.8, however each one either stopped down to f/4 or wide-open at f/4. Is there a major advantage to buying the f/2.8 if one is always using f/4? No. Since metering is done with the camera lens wide-open maybe the faster lens would meter a nanosecond faster.

However, what you are talking about is common in Canon's prime lineup...example 50mm f/1.0, 50mm f/2.5, 50mm f/1.8, 50mm f/1.4, and 50mm 1.2. Many will argue if you are always going to be at f/5.6 wouldn't you just buy the cheaper 50mm f/1.8? However, there are other characteristics to consider such as sharpness at the corners, vulnerability to optical abberations, contrast, etc. So even if all are stopped down to f/5.6 there can be other things to consider.

Back to your original question, the light gathering advantages go away stopped when stopped down. Maybe metering and autofocus are enhanced with the larger aperture lens since metering is done with the lens wide-open.

f4 is f4 is f4, and given the same lighting conditions and ISO will require the same shutter speed regardless of the lens's maximum apreture (ie. whether it's an f4, f2.8 or f1 lens). However, there are a some advantages to having a faster lens, even if you are shooting at f4 or below.

These include a brighter viewfinder (as the lens is wide open until you actually make the exposure and the f2.8 lens lets in twice as much light as the f4 lens), also the AF will respond faster with a f2.8 lens. Other things to consider are that the f2.8 lens might (I stress MIGHT) yield a higher image quality stopped down a stop, than the f4 lens wide open. Also if you want to use a 1.4x converter, the f2/8 only becomes a still very usable f4, whereas the f4 lens becomes a much darker f5.6 lens..The nifty low f-stop L lenses allows a shooter to capture pictures using a higher shutter speed with a lower f-stop (aperture). This is a great advantage when shooting sports.

[LoveDSLR]

Originally Posted by AlphaBjerke

Specifically, he had an expensive lens and I had a kit lens. We were both shooting at the same aperture and the same shutter speed, but he was able to shoot at 200 ISO when I had to shoot at 400 to get the same settings

Wow...Canon f/1.2 L lens is actually f/0.85.

What do you mean by 'same setting'? Other than different metering systems, different metering modes and lens manufacturing tolerance, you can shoot at the same EV as his (within your camera's aperture/shutter speed/ISO range). That's how we transfer EV reading from an Incident meter to our camera.

With wide apertures, you can select lower ISO or higher shutter speed with fast lenses for a given EV.

[AlphaBjerke]

Well, for the most part, all of you have told me things that I am already quite aware of. I understand the relationship between aperture and shutter speed. We were both shooting the exact same thing, so I doubt the metering would be different (the majority of the scene was mud--we were shooting a rodeo pointing down from the stands). He had a $3000 Canon, and I had a 500 dollar Sony. Unless I totally missed what he was saying he said that the clarity of the more expensive glass itself--not a larger aperture--allowed him so shoot at a lower ISO. He compared it too there being different grades of diamonds with the better rated ones having more clarity.

Anyway, thanks for helping out with the question!