Focal length 35mm equivalent, but not F-stop?

Started Jul 24, 2014 | Discussions thread
Tim Tucker Senior Member • Posts: 1,337
Re: Let's correct it, then.

Erik Magnuson wrote:

Tim Tucker wrote:

Erik Magnuson wrote:

Tim Tucker wrote: -

Is this the same as saying all f2 lenses transmit the same amount of light, but different sensor sizes collect different total amounts for the same exposure?

Amount is not a precise term. A 55gal drum and a 20oz red solo cup left out in the rain might both collect 1" of water. Is the same "amount" of water collected in each?

Eh? Total amount IS a precise term. Measure your volume in litres and you have a precise answer. But that is not what I asked.

It was the answer to your first question and use of "amount." All f/2 lenses do not transmit the same amount of light or my f/2 cell phone lens would transmit as much light as a 200mm f/2 lens. Even if I managed to put a 24x36mm sensor behind the call phone cam lens, it would not help much. What the lens transmits and what the sensor collects may be related, but they are not the same thing.

Sematics, as corrected by Lee Jay (my original statement above). Lenses for different formats do not have the same coverage therefore the total amount of light will not be the same but the light/square metre of sensor size (transmitted?) is the same at f2. A Super Angulon 90mm at f8 will produce the correct exposure regardless of whether I put 4"x5" film or 35mm film behind it.

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