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:

For the record the above shot was actually F1.7, 1/320 SS, ISO 125, used flash. I did however take several others before this one without flash using silent mode so as not to wake her while i chimp composition. This was the last shot, taken with bounce flash, but it still illustrates the DOF issues.

The only "issue" I see is that you have only just achieved your minimum tolerable DOF at close to the minimum focus distance of your lens. At any greater distance, you will lack DOF control that you could likely tolerate. Your example is akin to posting a macro shot with a P&S and talking about how much of an "issue" thin DOF is.

DOF isn't any thinner for macro than for a portrait, as a % of the frame, as long as both subjects are filling the frame. The reason macro "seems" thinner is because the scale is different compared to distance. In other words, your movement affects it more because you are closer, but the DOF is no different. If we are going to fill the frame with any common subject, like a car or a person's head/shoulders, the DOF will still be the same for the frame. DOF is going to cover a % of the frame, regardless of distance. Unless you know a 500' human that can fill the frame from far enough away to shoot at infinity, the point still stands.

Or do you never fill the frame with subjects when you shoot? If you don't then you will be further from the subject to match the DOF/ISO/F-stop, but then you have to crop every time, which lowers your affective ISO making the whole process moot. Ask around, look it up, it's the truth.

If you have a 10' tall giant with a huge head, and you have a small child with a much smaller head, you of course will have to stand at different distances to frame them the same (full head shot). But, shooting both at F2, you will have the same amount of each's face in focus, perhaps just the eyes, or the eyes and nose. Why? Because even though you are farther away from the giant, his features are also bigger.

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.

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.

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