Potential dead horse: how bad is FF's deep DoF disadvantage?

Started Mar 5, 2014 | Discussions thread
Ontario Gone
Ontario Gone Senior Member • Posts: 4,183
Re: SmartPhones and Shallow DoF - no large sensors needed

joejack951 wrote:

Ontario Gone wrote:

Here is a simple illustration. Two shots, same 45 degree angle, one shot a bit further than the other. Notice how even though they are both at F1.7, and they are of differing distances from the wall, the DOF makes up the same portion of the frame. Perhaps 15% the width of the frame. So no, if i want a subject to fill my frame and i need to use a lens at fast apertures like F1.7, distance ins't the culprit. In this case, FF will not give any advantage.

I don't believe you understand what you are saying (and I'm not so sure I fully understand it either). You are shooting with a 50/1.7 on m4/3 which equates to a 100/3.4 on full frame. I could frame exactly the same as you using a 105/2 or 105/2.8 lens on a full frame camera and create thinner DOF than your shots by virtue of the larger aperture.

Trust me, i fully understand what im saying, i will try to help you to as well.

PS- I know there is a formula for actual DOF for a given subject distance and a formula to equate that to the degree of FOV it matches to, i just don't care to look it up.


When you go there, you'll see that the DOF numbers are all distances, not percentages of the frame. Photographically, having some percentage of the frame in focus is quite meaningless.

Lets say your subject is a brick wall, and it is 5' away. Using a 100mm FOV lens (50mm on a MFT camera), at F2.4, you DOF is 2 inches (all these numbers are made up for the sake of the conversation). With your focal plane set to 5' in front of the lens (centered on the wall, and extending 1 inch in front and behind that as well), the distance from side to side of that focal plane will only be a certain length, perhaps 20 inches.

This all means that the DOF is going to be 1/10 of what the width of the in focus portion of the frame is. 2 inches is 1/10 of 20 inches. If you step forward or back x steps, the same ratio will exist. Take a shot 50 feet from a giant wall, with the width of your viewable DOF being 20' maybe. The DOF would be 1/10, or, 2 feet. These numbers are based on percentages and they don't change.

If you think about it, as you change your focal plane from near to far by adjusting your focus ring, the width of the scene's in focus area gets wider and wider, and the depth of that also gets deeper and deeper. They are connected, by percentage, and moving closer or further doesn't change that. Yes people refer to DOF by measurements, but there is also a percentage ratio that relates to the width of the focal plane.

I wish i could test this and prove it, perhaps i can to some extent but it is very difficult to illustrate exactly where DOF begins and ends, let alone define it the same among different people. The point still stands and it is correct.

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"Run to the light, Carol Anne. Run as fast as you can!"

 Ontario Gone's gear list:Ontario Gone's gear list
Nikon D7000 Canon EOS 70D Nikon AF-S DX Nikkor 35mm F1.8G Nikon AF-S Nikkor 50mm f/1.8G Canon EF 40mm f/2.8 STM
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