Help me to understand Hyperfocal Distance

[Dooglla]

Can someone tell me in simple terms how to understand about Hyperfocal Distance? I been looking and found charts and all but, still I am lost. Here is one I found but, can't figure it out for the life of me. And no, I am not dumb. hahahahaha

http://www.dofmaster.com/charts.html

[Scottes]

That link is not very informative. Here's one that may help a little bit: http://johnlind.tripod.com/art/artdof.html (the last section).
I have to say that I had a very tough time finding a decent explanation, but that article was the best I found.


My attempt at explaining it...
It is, simply put, the focal distance at which everything from one-half that distance to infinity is in focus.

So with a Hyperfocal Distance of 10 feet, everything from 5 feet to infinity is in focus, and sharp.

Although it's not always true, many/most people consider the Depth Of Field to extend about 1/3 in front of the focus point and 2/3 behind it. So if you set the camera to have a DoF of 3 feet then everything would be sharp from about 1 foot in front of the focus point to 2 feet behind the focus point.

Again, the "1/3 - 2/3" isn't entirely accurate but it's not a bad rule of thumb as long as you're not doing macro work or focusing on very distant objects.

We know that Depth Of Field extends somewhat in front of the focal point, and more DoF extends behind the focal point. So the Hyperfocal Distance is the focal point which still allows "infinity" to remain sharp. And now we see where the 1/3 - 2/3 rule breaks down, because when focused at the Hyperfocal Distance then everything from 1/2 that distance out to infinity remains sharp.


This link (http://www.johnhendry.com/gadget/hf.php) will allow you to make a custom Hyperfocal Distance chart for your lens. If you're using a 10D/20D/DRebel enter 0.019 for the Circle Of Confusion. Make one, print it, study it. Just vaguely remembering the values will help you in the field.


Sometimes this is tough in the field, especially when you forget the chart. So another rule of thumb is to focus on something slightly further away than the closest object you want to be in focus. As that distance lessens increase aperture. That is, f/8 is OK when the closest object is 10 feet away, but go down to f/22 if that object is 3 feet away.

Note that the above paragraph is very loose, and really pertains to wide angle lenses only. Don't attempt this rule of thumb until you create a custom HypFoc chart and get an idea of the numbers used for the focal length you use. Things are VERY different if you compare 17mm to 50mm, let alone 100mm.

The chart is definitive. The rules of thumb break down quickly.

[Dooglla]

Thanks Scottes...appreciate that much. I want to understand this to get the best pictures when I take them. I understand a little now from reading the article of what to do and using the chart will help. Thanks again.

[aam1234]

Thank you Scottes very much for the explanation. I copied & pasted it for future reference.

I have one question if I may.

"Again, the "1/3 - 2/3" isn't entirely accurate but it's not a bad rule of thumb as long as you're not doing macro work or focusing on very distant objects."

It's about macro. Does the above mean that the rule doesn't apply to macro or it's trickier to apply to macro.

Thanks again.

[Scottes]

It's about macro. Does the above mean that the rule doesn't apply to macro or it's trickier to apply to macro.

It really doesn't apply to macro, or to distant focus points. When doing macro it's better to think of the DoF being about 50% in front and 50% behind. When focusing on distant subjects you find that the far focus (furthest distance that's still sharp) is infinity. What is 1/3 of infinity?

Using this Custom DoF Chart Maker (http://www.johnhendry.com/gadget/dof.php) I used a 10D/20D with a 50mm lens at f/8 and calculated the DoFs for a subject at a distance of 0.5m, 1m, 2.5m, 5m, 7.5m, 10m, 15m, and 20m.

http://www.itsanadventure.com/postimages/dofchart.gif

At 0.5m we have 0.01m of DoF in front of the focus point, 0.01 behind, or 50% / 50%.
At 1m it's 45% / 55%
At 2.5m it's 42% / 58%
At 5m it's 35% / 65% (the 1/3 - 2/3 rule of thumb)
At 7.5 it's 27% / 73%
At 10m it's 20% / 80%
at 15m it's 5% / 95%
At 20m far focus is now at infinity, and can no longer be described as a percentage.

So you can see how sloppy the 1/3 - 2/3 rule is. In fact, now that I've calculated these percentages I'm going to throw that rule of thumb right out the window. It's a lousy rule. :grin:

[aam1234]

So you can see how sloppy the 1/3 - 2/3 rule is. In fact, now that I've calculated these percentages I'm going to throw that rule of thumb right out the window. It's a lousy rule. :grin:

Yeah! that's what I was thinking.

Thanks again for your effort.

[Dooglla]

Let me see if I got this right...if I have an 85mm lens, do I count also the 1.6 crop which would make it a 136 mm. I use the 136 to figure out the Hyperfocal Distance with 136 or just 85. And the CoC is 0.019.

[Scottes]

Let me see if I got this right...if I have an 85mm lens, do I count also the 1.6 crop which would make it a 136 mm. I use the 136 to figure out the Hyperfocal Distance with 136 or just 85. And the CoC is 0.019.

No. The Circle of Confusion of 0.019 takes the sensor size into account for 10D, 20D, and DRebel. A CoC of 0.025 would be for the MkII with 1.3 crop, and 0.030 for full frame (film and the full-frame 1D cameras). Use the appropriate CoC and the actual lens length of 85mm.

[Dooglla]

Ok...thanks again. I did it wrong and I am glad you were here to help me get it right. Also can I ask...with a lens that is 70-200 I use the longest length of 200 to figure out the HF?

[Scottes]

Depends on what you're zoomed to. Run a chart at 70mm and run the same exact chart at 200mm. You'll see a lot of difference!

IMHO HypFoc at 200mm isn't even worthwhile. Well, maybe I'm wrong. 200mm at f/22 it's 305 feet, so everything from 152 to infinity will be in focus. So it has some value.

As a comparison, at 70mm HypFoc is 37.4 feet. That's a heck of a difference.