Help me calculate/understand the physics of aperture, DOF and BG blur -

Started 7 months ago | Discussions thread
Darren James New Member • Posts: 12
Re: Help me calculate/understand the physics of aperture, DOF and BG blur -

Alright, now I’m cranky. Content warning: shade

I did the test. I stacked and aligned in photoshop. The D500 image lines up exactly perfectly over the middle of the D850 image. The overlapping results are identical. Same acceptable distance in focus in front of focal plane, same acceptable distance in focus behind. Same out of focus highlights. Same bokehballs.

Same samey same same. Again: the same.

If what you are actually telling me is that you’re blowing up the crop image to the same absolute size as the full frame image, printing them out, sticking them beside each other and standing 10 ft away, and therefore the out of focus highlights are physically bigger in the one image because you enlarged it, then all I have to say is DUH.

You can get the same results walking toward or away from a photo. Looks bigger up close. Why would anyone think that’s what anyone means when they say depth of field? Clearly, or I guess not so clearly, when a guy talks about depth of field in a photo it’s about what depth of field is acceptably in focus.


Depth of Field

  • n.In photography, the distance in front of and behind the subject that appears to be in focus.

But if what you meant to say was: enlarging a cropped image makes the things in the image larger compared to that same image where things are smaller then I guess I can’t argue with that 🤷‍♂️

sybersitizen wrote:

Darren James wrote:

If I understand correctly:

You’re saying if I take my D850 and any given lens, and stick it on a tripod and take a photo, then stick my D500 on the same lens changing nothing else, absolutely every factor the same, that the Depth Of Field changes?

I hope that’s not what you’re saying because that is completely incorrect. Wildly incorrect.

It's absolutely correct when you view both results at the same final viewing size, and from the same distance.

 Darren James's gear list:Darren James's gear list
Nikon Coolpix S33 Canon EOS 5D Mark III Canon EOS 6D Nikon 1 V2 Canon EOS 70D +12 more
Post (hide subjects) Posted by
Keyboard shortcuts:
FForum PPrevious NNext WNext unread UUpvote SSubscribe RReply QQuote BBookmark MMy threads
Color scheme? Blue / Yellow