A few words on Equivalence and comparing systems

Started Apr 2, 2013 | Discussions thread
Great Bustard
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Re: Please...
In reply to 69chevy, Apr 3, 2013

69chevy wrote:

Great Bustard wrote:

69chevy wrote:

Great Bustard wrote:

69chevy wrote:

So...

My camera phone has a crop factor of 7.64, the lens is 3.85mm and the aperture is f2.4.

The FF equivalent is 30mm f2.4?

No -- the FF equivalent is 29mm f/18 (3.85mm x 7.64 = 29mm, f/2.4 x 7.64 = f/18).

No disrespect, but if you are strictly talking DOF, this makes a little sense. If you are talking about diffraction effects or exposure effects it is not true.

...read the OP.  It's all discussed there (and yes, diffraction and exposure are discussed).

I did.

Excellent.  Then you understand that the efffects of diffraction softening and the total amount of light falling on the sensor is the same for 3.85mm f/2.4 on a 7.64x sensor as 29mm f/18 on a FF sensor for a the same shutter speed.

You can compare diffraction between two cameras with the same entrance pupil and different sensor sizes, but not with different flange distances and sensor sizes. This is where your equivalency formula falls short.

Um, no.  For more reading on diffraction and how it relates to different formats:

http://www.josephjamesphotography.com/equivalence/index.htm#diffraction

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