Does an f/1.4 lens at f/5.6 let in more light than f/4 lens at f/5.6?

sfogel2

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Hi, all...

Taking a random focal length, say 100mm, does a 100mm f/1.4 lens stopped down to f/5.6 let more light hit the sensor than a 100mm f/4 lens stopped down to f/5.6?

Thanks
 

nerwin

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Nope, it's physics.

f/stop is the amount of light that is allowed to hit the sensor. f/4 on a 50mm is the same as f/4 on a 100mm. Now....because the latter is 100mm, you'll have an increase in shallow depth of field BUT the amount of light coming through is the same as the 50mm at the same aperture.

I may be wrong, but that's how I understood it.

I even did a quick test.

Nikon D610 + 16-35 f/4 VR
1/200th, f/5.6, ISO 400

Erwin-170712-12263.jpg


Nikon D610 + 50mm f/1.8G
1/200th, f/5.6, ISO 400

Erwin-170712-12264.jpg


It's the exact same exposure despite different lens. Now there might be a slight difference in brightness and colors that's just because they were different lenses. The 16-35 has many more elements and what not. They also produce slightly different colors. But the meter was reading the exact same exposure.

However, the difference of the f/1.4 vs f/4 100mm lens would be the viewfinder. The f/1.4 will be MUCH brighter and could possibly aid in autofocusing, but I'm not sure. If you are using a DSLR, use the depth of field preview button to toggle between wide open and stopped down to see the difference in the amount of light that is coming through the lens.

Hope this helps!
 
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Derrel

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In terms of actual T-stop, or Transmission stop, an f/1.4 7- or 8-element prime lens might actually admit more light than say, a 17- to 23-element f/4 zoom lens, due to light loss from so many air-to-glass surfaces in the zoom lens. At times, people refer to one lens as being "brighter than" another lens, at the same marked f/stop value, or across the range of f/stops.

Cine lenses are typically these days marked in T-stop, not f/stop. One is the actual transmission of light, the other is a pure relationship to focal length value.
 

KmH

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Light is lost in a lens in each glass lens element because some amount of light gets attenuated by the glass.
In comparison air gaps between lens elements attenuate little if any light because air has so much less density compared to glass.
 

Bebulamar

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They are supposedly the same at f/5.6 but one lens is brighter than the other most likely but you wouldn't know which one without testing.
 

Vtec44

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I'd think the lens diameter and coating would have a big impact on how much light can reach the sensor. I'm not a technical person though ...
 

fmw

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Hi, all...

Taking a random focal length, say 100mm, does a 100mm f/1.4 lens stopped down to f/5.6 let more light hit the sensor than a 100mm f/4 lens stopped down to f/5.6?

Thanks

The purpose of the f number is to create a standard that photographers can use to set the aperture regardless of the lens in question. For a number of reasons there could be some slight variations from lens to lens but not enough to cause the photographer to change the f number selected. Basically f5.6 is f5.6 on any lens - at least in intent and theory.
 

benhasajeep

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100mm f/1.4 lens set at f/5.6 the aperture hole is 17.86mm. On a 100mm f/4.0 lens set at F/5.6 the aperture hole will be 17.86mm. There is a reason F#'s are written as f/x.x. This is because aperture is expressed as a fraction of lens focal length with ‘f’ standing for focal length. To determine the opening in the aperture at a setting. You divide the lens length in mm by its aperture setting. Hence in the examples above. 100/5.6 = 17.85714xxx.

Now with a 100mm f/1.4 lens and a 50mm f/1.4 lens. Both set at f/4.0. They WILL have different aperture opening sizes. 100mm @f/4 would be 25mm. 50mm @ f/4.0 would be 12.5mm.

Same settings on same focal length, yes they would match. Same setting on different focal length lenses no they will not match.
 

fmw

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Now with a 100mm f/1.4 lens and a 50mm f/1.4 lens. Both set at f/4.0. They WILL have different aperture opening sizes. 100mm @f/4 would be 25mm. 50mm @ f/4.0 would be 12.5mm..

yes, but the OP is talking about a 100mm lens in both cases. And he is asking if one will "let more light in" than the other. The answer is basically no. With minor variations, the same amount of light will reach the sensor with either lens.
 

Dragster3

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I don't know if the answer is totally no, I'm no expert, but I remember 20+ years ago when I was heavy into photography, with my spotmatic, if I set say f5 and you zoom out the spot meter goes up, there is a correction in f stop with zoom lens. I say set camera at certain manual setting, then change lens and see what lens is brighter. I don't know...
 

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