Hyperfocal distance.

Without getting into photography jargon, this one topic has eluded my brain for many many months. I still just don't have a clue what it means. Here's what I think it means:

Despite a wide aperture, everything remains in focus. A shot taken at 1.4 will not blur or cause bokeh. Is this right?

No, it is not..
It is little bit more complicated, I’m afraid:

With this particular aperture, at this particular focal length, when focused at this particular distance, everything between half of that distance and infinity will be in focus.

I think I understand. I'm standing on the 1st yardline of a football field. I focus 5 yards in front of me at f/1.4. Everything from yard 2.5 to infinity will be in focus?

That is correct!
If you focus at ½ of the hyperfocal distance, everything will be in focus.
Note that hyperfocal distance has to be calculated each and every time you change one of the parameters that influence it: aperture, focal length or camera format.

Thanks hermeto! I feel smart now! Thanks a lot!

Play around with a DOF calculator and discover the effects of how hyperfocal distance changes with aperture and focal length.

I've seen DOF calculators and they scare the **** out of me. I have no idea what the hells going on or how to read one.

Nothing scary about DoF calculator.

You simply enter your camera model (which defines Circle of Confusion), focal length of the lens being used, aperture value and distance from camera to subject.
Click Calculate and it spits out all that you have to know about depth of field.

http://dofmaster.com/d​ofjs.htmlhttp://dofmaster.com/d​ofjs.html

Circle ones that you have to rotate are the same thing.
Print one and assembly it, play with it for a while and you’ll see that everything is self explanatory.

http://dofmaster.com/c​ustom.html

Hyperfocal distance is nothing but the fancy name for maximum depth of field - under the circumstances.

Hermeto wrote in post #3054205
http://dofmaster.com/c​ustom.html

nice custom printouts there, thanks for the link.

Customizing your CoC Diameter and avoiding diffraction

Perhaps the greatest source of disappointment when using a DoF calculator like those generated with the DoFMaster software (which I heartily recommend), comes from failing to understand that a single choice of Circle of Confusion diameter can not possibly satisfy every combination of print size and viewing distance you might produce with a given camera. And where is it written that your definition of "sharp" is the same as everyone else's?

Don Fleming has made a valiant effort to simplify the selection of Circle of Confusion diameters, as seen at this page:

http://www.dofmaster.c​om/digital_coc.html

All the values shown there for various makes and models of digital cameras are based on the sometimes tragic assumption that everyone who uses DoFMaster, including you, is absolutely content with the DoF had when using a diameter of 0.03mm when shooting with 35mm (full frame) cameras. All the values are scaled from this reference value. (He says so at the top of the page.)

The online Circle of Confusion calculator he offers at the bottom of that page allows you to input YOUR choice of a CoC diameter for 35mm (full frame), so that it can calculate a CoC diameter that's scaled proportionately for your digital camera.

The problem is that even if you are among that minority that realize you can change this value to suit your needs, Don doesn't tell you how to go about doing so.

Many people would agree that a DoF calculator, or tables, or the engravings on your lenses, calculated using a CoC Diameter of 0.03mm for 35mm (full frame) is simply NOT small enough to produce "sharp" Nears and Fars in prints made as large as the format otherwise permits. The fact is that lots of people have abandoned the use of DoF calculations precisely because they have not been satisfied with the results.

But there is nothing inherently wrong with the mathematics of Depth of Field. The PROBLEM is that most people are treating CoC diameters as a CONSTANT for DoF calculations instead of as a VARIABLE.

If you intend to make 8x10 prints to be viewed at a distance of 10 inches, your DoF calculations can be made using a CoC Diameter that is TWICE the size of the CoC Diameter required for making 16x20 prints from the same camera. For 8x10 prints, this translates to a greater range of subject distances at a given f-Number -OR- a smaller f-Number (wider aperture and faster shutter speed) for a given subject distance.

Similarly, If you intend to make 11x14 prints to be viewed at a distance of 20 inches, your DoF calculations can be made using a CoC Diameter that is TWICE the size of the CoC Diameter required for making 11x14 prints that will survive scrutiny at a viewing distance of only 10 inches. For the 20-inch viewing distance, this translates to a greater range of subject distances at a given f-Number -OR- a smaller f-Number (wider aperture and faster shutter speed) for a given subject distance.

Lastly, if you have a personal requirement for producing prints that retain subject detail right up to the limits of what healthy human vision can resolve (about 8 lp/mm), the CoC Diameter you use for DoF calculations will have to be HALF the size of the CoC Diameter used by someone who is content with a print resolution of 4 lp/mm (all else being the same.)

Wikipedia's article on Circle of Confusion, states that there are three factors affecting the selection of the CoC diameter for use in DoF calculations:

1) The acuity of the human eye
2) The anticipated viewing distance
and
3) The anticipated enlargement factor

See: http://en.wikipedia.or​g/wiki/Circle_of_confu​sion

Here is a formula (which I contributed to that article) that takes all three of these factors into account:

CoC Diameter Limit (mm) = anticipated viewing distance (cm) / desired print resolution (lp/mm) for a 25 cm viewing distance / anticipated enlargement factor / 25

(25 cm is equivalent to about 10 inches.)

For example, to support a print resolution equivalent to 5 lp/mm for a 25 cm viewing distance when the anticipated viewing distance is 50 cm and the anticipated enlargement factor is 8:

CoC Diameter Limit = 50 / 5 / 8 / 25 = 0.05 mm

If you are among those who always want your prints to survive scrutiny at a distance of 10 inches (25 cm), you can use a simpler version of this formula:

CoC Diameter Limit (mm) = 1 / desired print resolution (lp/mm) / anticipated enlargement factor

For desired print resolution, I recommend a value in the range of 3 to 8 lp/mm. As you increase this value for use in the DoF calculator of choice, the CoC diameters in your final print, after enlargement, will become smaller - less visible at the Near and Far extremes of the subject space.

Enlargement factor is simply the diagonal of your intended print dimensions divided by the diagonal of your digital sensor or film frame.

I recommend you create a DoFMaster spinning disk calculator for every combination of focal length and print size (and anticipated viewing distance) you intend to produce. I carry several in my camera bag - they weigh next to nothing and they don't consume any space to speak of, so why not?

If you have no intention of making prints at more than one size, you should at least do yourself the favor of customizing your CoC diameter to satisfy your one combination of desired print resolution, anticipated enlargement factor, and anticipated viewing distance - INSTEAD of naively using a CoC diameter that's scaled from the archaic 0.03mm standard CoC diameter used for 35mm cameras.

While you're at it, consider doing one more calculation for each of the DoF calculators you produce: Determine the f-Number at which diffraction will inhibit your desired print resolution. There is no point stopping down for additional DoF if doing so will force diffraction's Airy disks to become larger than your chosen Maximum Permissible CoC Diameter. Diffraction degrades the entire print uniformly. It makes no sense to visibly reduce the resolution of the entire image in an attempt to make the Near and Far sharps of the subject space acceptably sharp.

Here's a formula for determining the f-Number at which diffraction will inhibit your desired print resolution, having previously calculated the Max. Permissible CoC Diameter using one of the formulas I've provided above:

N = Max. Permissible CoC Diameter / 0.00135383

For example, if you are using a CoC Diameter of 0.015 mm for DoF calculations, the f-Number at which diffraction will begin to inhibit your desired print resolution would be:

N = 0.015 / 0.00135383 = 11 (or f/11)

I recommend you write this diffraction limit f-Number on the DoF calculator that was produced using the specified CoC Diameter, then, whenever your DoF calculator suggests that your subject space requires an f-Number GREATER than the calculated diffraction limit f-Number, you'll know that the DoF requirements of the subject space are too great for your specified combination of desired print resolution, enlargement factor, and anticipated viewing distance. You'll then be confronted with these choices:

1) Compromise your standards by shooting at the DoF calculator's recommended f-Number even though it exceeds the f-Number at which diffraction will begin to inhibit your desired print resolution. (Yuck!)

2) Move away from the nearest subject to decrease your DoF requirement until the DoF calculator indicates that you're far enough away to get sufficient DoF with the calculated diffraction limit f-Number.

3) Don't move the camera, but decrease your focal length until your DoF calculator (for the new focal length) indicates that you can use the calculated diffraction limit f-Number for sufficient DoF.

4) Resign yourself to making a smaller print, until the DoF calculator for that combination of focal length and print size indicates that the diffraction limit f-Number will provide sufficient DoF.

-or-

5) Put your camera back in the bag without shooting.

Mike Davis
http://www.accessz.com

Hyperfocal distance is that focusing distance that, for a given aperture and sensor size, will just barely place the far limit of the depth of field at infinity. The near limit of the depth of field will then be at approximately 1/2 the hyperfocal distance.

That means, when a lens is set to its hyperfocal distance, everything from about one-half that distance to infinity will be in acceptable focus. This is the greatest possible depth of field for that focal length, that aperture, and that sensor size.

This is how they set the focus of pre-focused cameras (box cameras) so that the greatest possible depth of field is obtained.

In the days of manual-only cameras, many professional photographers, especially photojournalists, would set their cameras for walk-around with the aperture at f/8, the shutter speed at daylight with the film they were using, and the focus at the hyperfocal distance for the focal length of the lens. This left the camera ready to point and shoot instantly, thus enabling the capture of shots that would have been lost if the photographer had to fiddle around with focus. (The famous shot of a jet coming down in flames over San Diego comes to mind.)

These days, hyperfocal distance is best determined by a DoF calculator. In the old days, it could be obtained directly from the lens DoF scales. This is an "advancement" that I personally deplore.

zilch0md wrote in post #3057782
... where is it written that your definition of "sharp" is the same as everyone else's?

... you should at least do yourself the favor of customizing your CoC diameter to satisfy your one combination of desired print resolution, anticipated enlargement factor, and anticipated viewing distance - INSTEAD of naively using a CoC diameter that's scaled from the archaic 0.03mm standard CoC diameter used for 35mm cameras.

Wow. Thanks for the post, Mike. I thought I understood DOF and I don't have any trouble following the maths that's involved here, but you made a couple of very good points that had passed me by. I shall certainly bear this in mind from now on. Thanks again.

StewartR wrote in post #3062140
Wow. Thanks for the post, Mike. I thought I understood DOF and I don't have any trouble following the maths that's involved here, but you made a couple of very good points that had passed me by. I shall certainly bear this in mind from now on. Thanks again.

You're very welcome! It's always nice to discover that someone agrees with what you've written, whatever the topic, but I'm especially appreciative of your feedback here. You give evidence that a dent has been made in the nearly universal failure to appreciate the impact of CoC selection on DoF calculations.

Mike Davis
http://www.accessz.com

It was certainly an awful lot easier when the DOF scale was on the lens itself. But that's not really practical with zoom lenses. Easier with a prime, but even they don't have a decently readable scale anymore.