Sensor sizes and f stops

Started 8 months ago | Discussions thread
Christof21
Senior MemberPosts: 1,022
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Re: f-numbers are independent of sensor size
In reply to darklamp, 8 months ago

darklamp wrote:

I wonder if there´s a way to directly correlate sensor size and fstop

The way exposure system values work is that they are designed to give the same exposure on different systems, regardless of sensor size ( or film size ).

So there is no correlation between sensor size and f-number.

What is sometimes done is to calculate an equivalent f-number for a system to relate it to another. This is normally based on depth of field formula. However this ONLY relates to depth of field. You can also calculate the absolute size of the aperture from the f-number and the sensor size and compare them that way.

While there are small differences from system to system, using the same ISO, shutter speed and aperture (f-number) will result in the same exposure.

Well, not really...

There is a correlation between sensor size and f-number. You can calculate an equivalent f number by multiplying by the crop factor. And it works for dof (same resulting dof) AND for the "light" ( same quantity of noise in the resulting image). You just have to stop down with the larger sensor and to raise the ISO to compensate.

The following link may help:

http://www.josephjamesphotography.com/equivalence/

Inthink this is the most misunderstood concept in photography....

So F1.8 with a P&S is like having F10 with a FF . See the difference ???

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