A few words on Equivalence and comparing systems

Started Apr 2, 2013 | Discussions thread
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Great Bustard OP Forum Pro • Posts: 36,983
Re: No you did not, or ...

69chevy wrote:

Great Bustard wrote:

69chevy wrote:

forpetessake wrote:

69chevy wrote:

Great Bustard wrote:

69chevy wrote:

Great Bustard wrote:

69chevy wrote:


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.

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.

You either didn't read or did not understand. If it's the latter, then there is no shame in asking questions, but making arrogant statements is a completely different matter.

Diffraction isn't just related to aperture. It is also a function of sensor size. It is not arrogance, it is true.

When diffraction occurs the light is bent into a disc shape. As sensor size decreases, the pixel size does as well.

This means that the closer together the pixels are, the more diffraction affects the image.

Sorry, but that's all incorrect.  Again:


In short, diffraction softening is a result of the proportion of the photo that the Airy Disk spans, and that proportion is the same for all systems at the same DOF, regardless of sensor size or pixel count.

So you agree the disc size grows?

No.  For a given DOF, the size of the Airy Disk spans the same proportion of the sensor on all systems.  How many pixels that disk covers is irrelevant.

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