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

Started 6 months ago | Discussions thread
joejack951
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Re: SmartPhones and Shallow DoF - no large sensors needed
In reply to Ontario Gone, 6 months ago

Ontario Gone wrote:

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.

Your percentage of the frame argument has little to do with photography. I want a specific subject in focus, not a percentage of the frame regardless of framing. And your percentage of the frame at a 45 degree angle equates to a specific distance (also known as the depth of field) and it decreases as you focus more closely (everything else held equal).

Regardless, with a larger format, for the same composition, I can get thinner DOF than I could with m4/3. As I've explained, if you've only hit the point of too little DOF at the minimum focus distance of your lens, backing up more to change framing will mean that you now have more DOF than you need/want.

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.

I understand the effect of cropping. I frame to capture the scene I want, which may or may not fill the frame with the subject. Unless I'm focal length constrained or make a mistake in my framing choice, I don't shoot with the intent to crop later.

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.

Ok. I'm not sure what point you are trying to make here. Maybe I want only one eyeball in focus. Maybe I want to be further away and still only have one eyeball in focus versus the whole body. Or, more commonly, maybe I'm further away still but only want the whole body in focus instead of the whole body and background.

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.

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.

www.dofmaster.com

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.

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