DOF and Cropping take 2

Started Feb 11, 2014 | Discussions thread
Ian Stuart Forsyth
OP Ian Stuart Forsyth Veteran Member • Posts: 3,238
Re: DOF and Cropping take 2

moving_comfort wrote:

awaldram wrote:

moving_comfort wrote:

Actually it's not what you've been saying - you've been saying that cropping FF to aps-c of a shot taken from the same position and then displaying the same size does not alter DOF - and it does. It makes the FF shot equal the aps-c shot in DOF, when before (uncropped) it had less DOF. See how the DOF changed there, by cropping and enlarging to the same viewing size?

it never ever had less or more DoF it always had the same DoF if you don't understand that point I'm close to giving up.

It did not have the same DOF until you changed the viewing size by cropping and enlarging! Which is what I and other have been trying, and trying, and trying to get across to you.

and trying


100mm f/2.8 FF @ 10 feet does not have the same DOF as 100mm f/2.8 aps-c @ 10 feet. Correct? Let's consult:

* Using the same lens on a APS-C crop sensor camera and a 35mm full frame body, the APS-C crop sensor camera image has 1.5x LESS depth of field than the 35mm image would have

So I assume you won't argue the point above, and agree that it's correct. Moving on...

However if you crop the FF shot to be the same FOV as the aps-c shot and display both at the same size (screen, print wherever) then they both do have the same DOF. Correct? Let's consult the bible:

* If you use the same lens on an APS-C crop sensor camera and a 35mm full frame body and crop the full frame 35mm image to give the same view as the APS-C crop image, the depth of field is IDENTICAL

So, you'll have to accept that. Let's move on to the question:

What changed? At first, the FF image had less DOF, now it has the same - what changed? You cropped the FF image and enlarged - thus, cropping changed it's DOF!

You keep saying that cropping cannot change DOF, but it demonstrably does - unless you say the above is false.

You were making the exact same mistakes in that thread from three months ago, which is why I keep referencing it - I'm making the same arguments, as is Ian and others, and you keep saying "cropping cannot change DOF" when we keep showing you otherwise.

In fact I know where you're getting it wrong, and have tried to point it out, but you won't listen - you keep looking at the cropped piece and not fully realizing that what you've done is enlarge them to the same dimensions, thus equalizing DOF. And I don't know how to make you 'hear' that, because at this point I don't think you want to hear 2 + 2 = 4 from me. Maybe someone else can give it a shot and you'll listen to them.


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