Sensor sizes and f stops

Started Jan 25, 2014 | Discussions thread
Christof21 Veteran Member • Posts: 3,506
Re: No correlation

starlight110 wrote:

Christof21 wrote:

It is very important to be aware of this. The op could buy a f1.8 with a1/2.3" thinking that it is better that a f2.8 with a 1" sensor. The 1" sensor is better for dof AND low light conditions.

That´s about what I ment with my original question, sorry if I didn´t express it correctly since my english is not the best and I´m newbie in photography.

I will put a simple example. Let´s say I want to compare two ideal cameras. Both have ideally fully manual controls and have the same lenses. One has a 1/2,3´sensor and the other 1/1,15´,, double in size, same megapixels and of the same type. I take a picture with the two cameras in the same light situation and setting in both iso100 and 1/30 sec exposure. The cameras have exactly the same algorithms to determine the aperture so that the amount of noise is about the same, in this case would there be a difference in aperture?? if yes, how much in terms of fstops??

No difference in aperture because the exposure rules are the same (triangle of exposure) whatever the sensor size is.

BUT you will have less noise with the larger sensor ! This is what is important. The difference is in fact 2 stops in favor of the larger sensor.

You could say that the larger sensor is the winner. Not that simple. In your example, you omit to say that when you take the same picture (same framing=same angle of view) , you will have less dof... So having this advantage of 2 stops is not free, you will have less dof.. If you stop down the larger sensor, you will have a similar picture in fact. With the  larger sensor, you have more choice in fact: you can get a similar picture or decide to have a shallower dof and more light. You do not have this choice with small sensors, it would need lenses with very low f number which do not exist.

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