Hi, As I understand it Hyperfocal distance should in theory give you an image from 1/2 behind your focus point to infinity, so focus 12' would be 6' to infinity and from what I have found out apart from focus stacking this should give as stated a sharp in focus image but what I cannot see is that if you use like I am trying to do the DOF master app and it says for example set your lens to 2ft for your distance for everything to be in sharp focus but on my lens (Canon 17-40mm) the scale 1ft, 1.5ft then 3ft if you have to guess where the 2ft is on the lens then what is the point in having the app or even a scale sheet?
What am I missing please?
Many Thanks
Russ
Hyper-focal distance is just that distance a lens of a particular focal length and selected aperture needs to be focused such that 'infinity' will be in focus. Due to optical properties, everything from 1/2 the hyper-focal distance (focused distance of the lens) and infinity will be in focus. Rolled in there are assumptions on the amount of enlargement and preciseness of focus required as expressed in the Circle of Confusion (CoC) used in the calculation.
First, I recommend you do some tests in the back yard or somewhere using different CoCs for your camera until you find a number that works for you and your needs. You can start with printed numbers for different cameras/sensor size. But you may or may not be satisfied with these generalized numbers. Nothing beats seeing it for yourself. You will never understand fully until you do. And once you do, it will start to be second nature. You will start looking at a scene and just know, Damn, I'm going to need f/16 or better for this.
In the field, don't get bent around the axle. Identify the closest object you need in focus. Determine the distance by whatever means possible; camera auto or manual range finder, tape measure, stepping it off, etc. Now from a set of tables or printed charts or phone HF calculator, determine the necessary aperture needed such that the hyper-focal distance is less than or equal to 2x the nearest object distance. I wrote my own that takes the near distance, focal length and my CoC and gives me the required aperture. I also use the Depth of Field Preview feature of my camera, alot!
Here is where the photographic decisions start coming in. First, you know how 'critical' your DoF will be based on the CoC you have established. You can alter the aperture one way or the other based on the current needs versus your 'standard'. In addition, you need to look at ISO and shutter speed. Can you make the aperture work given the lighting, movement, quality needs. Finally, you need to be aware that as you stop down the lens, you are trading focus blur against diffraction blur. It is usually a pretty good trade off, but it is there, especially if your camera has tiny pixels like the 24MP DX Nikon D7100 I shoot with sometimes at 3.9 microns versus 5.9 microns of the 24MP FX format D750.
Here I will put a plug in for my pet lament. If only cameras would allow loading and running 3rd party apps. A little app that would take the focused distance of the lens (as focused on the near object), the focal length the camera is reporting, my pre-loaded CoC and not only tell me the aperture to use, but set it on the camera! The 1st camera maker that understands how valuable they can make their cameras by allowing extensibility and specialization is going to make a bundle. Unfortunately, I doubt it will be either Canon or Nikon!
