Beginner Question of light and lens difference

[SsSsSsSsSnake]

Take 2 lenses .1 a fast 1.2 prime and the other a slower F4 zoom.

both at F8 would the amount of light be exactly the same?

thanks

 

[johnnypanic]

Yes.

 

[Kodiak Qc]

•
YES! …or let's say that it should be.

The ƒ number indicates the amount of light reaching the chip/film vs the amount of light available.
ƒ1 means that the available light is being 1:1 projected on the chip/film.
ƒ 1.4 means that the light reaching the chip/film is half the amount of light available.
ƒ2 means that the light reaching the chip/film is a quarter the amount of light available.
etc.

• All/any lens, at ƒ8 will project the same amount of light.
• The aperture being a somewhat "absolute value" relative to the amount of available light.

 

[Phil-D]

My answer is yes Chris, f8 is........ f8, but happy to live and learn if wrong

Edit- Must type faster....but at least it looks like I was right

 

[rpsmith79]

However, you would expect IQ to be better from a Prime lens compared to a Zoom (comparing lenses in a similar price bracket anyway) as zoom lenses have to make certain compromises due to the nature of it being a zoom lens

 

[SsSsSsSsSnake]

Ah Rich,I thought someone might mention that and I am certain that is the case but I purposely left that out of the question to not complicate the answers
thankyou

 

[Phil V]

However, you would expect IQ to be better from a Prime lens compared to a Zoom (comparing lenses in a similar price bracket anyway) as zoom lenses have to make certain compromises due to the nature of it being a zoom lens

Although at F8, most lenses should be performing well enough that it'd be difficult to tell...

Which is where all the 'kit lenses can take awesome photos' posts come from. Landscape shooters with fantastic technique and great tripods telling us all that there's no need for more expensive lenses. Completely ignoring the fact that a lens sharp at 1.4 is usually without a rival, not to mention a lens that'll focus on a moving cat in a coal cellar.

 

[SsSsSsSsSnake]

Although at F8, most lenses should be performing well enough that it'd be difficult to tell...

Which is where all the 'kit lenses can take awesome photos' posts come from. Landscape shooters with fantastic technique and great tripods telling us all that there's no need for more expensive lenses. Completely ignoring the fact that a lens sharp at 1.4 is usually without a rival, not to mention a lens that'll focus on a moving cat in a coal cellar.

And a black cat at that eh Phil

 

[Alastair]

Take 2 lenses .1 a fast 1.2 prime and the other a slower F4 zoom.

both at F8 would the amount of light be exactly the same?

thanks

For most uses the difference in the light at the sensor plane will be negligible, and effectively the same. But measured closely enough it's unlikely they would be exactly the same.

The f/value does not directly measure the light passed through the lens. For the light falling on the sensor plane to be the same the t/value of the two lenses would have to be the same, this measures the transmission of light taking into account the absorbance of light within the glass elements of the lens.

 

[StewartR]

The f/value does not directly measure the light passed through the lens. For the light falling on the sensor plane to be the same the t/value of the two lenses would have to be the same, this measures the transmission of light taking into account the absorbance of light within the glass elements of the lens.

Beat me to it!