DOF and Cropping take 2

Started Feb 11, 2014 | Discussions thread
Ian Stuart Forsyth
OP Ian Stuart Forsyth Veteran Member • Posts: 3,235
Re: What the heck is a cropped image ( with the 645d)

awaldram wrote:

So your now agreeing a crop from a larger is identical to the the smaller sensor - hallelujah.

and I see your also changing your mind

But if we look at all of the crops they all have different FOV and DOF and this test shows that the format indeed has changed DOF. DOF for the 645 DOF 3.6cm DOF for the FF 2.1cm DOF for the APSC 1.44cm and DOF of the Q0.36cm

and this would mean that F2.8 is not equal to F2.8 on MF to the Q


"Where quite obviously sensor size effects the standard viewing distance and so neither DoF or lens characteristics are altered at all as 'that pesky physics' states.

i.e a 300F2.8 lens is 300mm and f2.8 whether on MF, FF or Q"

Format does not affect the standard viewing distance as a 8x10 print off a MF is the same size as a 8x10 print of a FF and would be view at the same distance and because of this you see different DOF for the same F4 across different formats. If I was to print both at 2 foot wide prints and you sat back and looked them at the same distance the DOF would be different If I looked at them up close the DOF would still be different

Only when you look at the subject at the same magnification is where you would see that they would have the same DOF as see here but then in effect you would be looking at them as if they were captured by the same format with different FOV (Visual Cropping)

Only thing that remains the same is the exposure as that is derived using F/2.8 but this is irrelevant as all 4 formats capture different amounts of total light and total light is what determines noise in the final image

But here's the problem a ff lense to equal your 300 F4 would only have to be a FF 400 f5.6 equivalent lenses same DOF same more or les the same FOV and the same total light gathered so the same noise and that lens comes to the same price point of a 300 F4

And here lies your problem holding ISO across format is irrelevant as iso 100 on cropped is the same as iso 225 on ff

You made all these claims they can't all be true.

Total light gathering is irrelevant , per pixel light gathering determines noise.

The d800 with the same pixel density as 16 mp aps-c sensor unsurprisingly has the same noise and dnr.

the d800 is in effect a seamless bonded dual aps-c a technology that dramatically reduce per ff sensor manufacturing costs.

I think I see what your doing in your head your trying to equalize all figures to FF so you multiply any aps-c specs by 1.5 to get FF gold standard !

So you take iso100 it becomes 225 , an f2.8 lens becomes f5.6 , noise is reduce by 1.5 time due to magnification factor etc etc

If only life was that simple the reality is massively different and easily proved as you keep doing with your image posts which vindicate my point not yours so not sure why your posting them.

Hey just realized I can do the same trick to prove my K3 has less niose than the k5 above 32,000

I just divide the real noise figure by 1.5 (24/16) to equalize outputs at a set 16mp

Hey if I do it for the pixel density Vs the d800 I can probably prove the K3 is the lowest noise camera ever made at all ISO's

Or do you think people might complain I'd lost the plot, Which is exactly as I view your 'equivalence mantra'

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