DOF and Cropping take 2

Started Feb 11, 2014 | Discussions thread
awaldram Forum Pro • Posts: 13,248
Re: U R Slippery II

Ian Stuart Forsyth wrote:

awaldram wrote:

moving_comfort wrote:

By the way, can you explain how you changed your story on this answer you gave below?


You changed your story on that, which represents progress - what made you change?

As I said earlier I'm bored with this now but have to pull you up on that miss quoting

you said

you I used to hold the position it does not (change DoF when displayed at same size)

I did do and always will do , Ian posted examples that prove it , I posted examples that prove it, and both James and myself posted algorithms that prove it.

No amount of trying to make something different will alter that.!

DoF is relative to magnification.

Equivalence as defined by you ,Ian and Lumo is just wrong and misleading.

A lens does not change any of it characteristics ever !

Altering Focal length aperture etc as you change format to produce a similar image and then stating it is equivalent is based on the idea the larger format is superior to the smaller.

Often it is not often the smaller format has higher pixel density , lower relative noise, more efficient pixels or better DR this then completely breaks you equivalence.

take a 6mp FF and a k5 run you 'equivalent ideas to create ti 'equivalent pictures.

Only they wont be the FF will be noisey and grainy

How come ?

take these to images as I asked before both shot from an external light meter reading why are

A very simple question, at the single photocell level why does the K 5 pixel show up as bright as a Q pixel when both are shot at the same shutter speed, Fstop and iso when viewed on the back of the camera. We know that the k5 photocell is several times large than the Q’s giving the k5 photocell more light whereas the Q’s is smaller and would receive less light. This should make k5 image way brighter as it has captured more light right?

  1. The photocell of the Q is several times more efficient at gather light so it would show up as bright
  2. That all sensor have a gain applied to them to bring them up to the same brightness to meet the standard iso rating and make up for the smaller photon count of a smaller photocell
  3. Physics is out the window
  4. Size of the photocell has nothing to do with how much light is gathered

That is simple we have a standard that define how a film/sensor/plate will react to the amount of light it receives.

It called ISO and is constant for any given luminosity cameras are calibrated to it and DXO measure how much those manufacturers egg the cake (erm hello Nikon)

So irrelevant of sensor efficiency or size (light density) a camera will have the same exposure solution for the same ISO set.

What will alter is noise levels as the more efficient a sensor at capturing light be that  through size or well the lower gain it will need to 'calibrate' to the ISO scale.

As this calibration is outside user control you cannot alter it all you can do is prove it existence by showing the exposure is constant across sensor sizes for the same lens and aperture used (at 18% grey)

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