Is this hyperfocal calculator wrong?

Tamron SP AF 17-50mm f/2.8 Di II LD Aspherical (IF) for Nikon

07/31/2007 08:17:44 PM · #1

I understood two things about hyperfocal distance. If you focus at the hyperfocal distance, then:
1)the DOF runs from half the hyperfocal distance to infinity and
2) the DOF is as deep as possible (total range in focus is the largest)

Yet two hyperfocal distance calculators online say otherwise.

For example, look at this one.

Plug in Nikon D200, 280mm focal length, and F/5.6, and you get a hyperfocal distance of 2274.4 feet. So if you plug that distance into the subject distance, indeed, the DOF goes from 1137.2 to infinity. So far, so good.

But if instead I use 1900 feet for the subject distance, it says the DOF goes from 1035.2 feet to infinity. In other words, the DOF is now more than 100 feet larger, and closer.

Is this just an approximate formula breaking down, or am I misunderstanding something?

BTW, this calculator gives exactly the same results.

Thanks.

ETA: I found the actual equations, so I think the online calculators are just set to call pretty far distances infinite even when they're not really.

Message edited by author 2007-07-31 20:23:36.

jrdawson

Canon EOS-350D Rebel XT

Canon EF 17-40mm f/4.0L USM

07/31/2007 08:22:52 PM · #2

Odd... my understand is the same as yours. I'm not sure what's going on.

Tamron SP AF 17-50mm f/2.8 Di II LD Aspherical (IF) for Nikon

07/31/2007 08:24:02 PM · #3

I think the calculators are just calling far distances infinity even when they're not, so no real problem.

Canon EF 17-40mm f/4.0L USM

07/31/2007 08:30:49 PM · #4

From the page explaining the calculations:

Originally posted by "Nikonians":

NEAR FOCUS LIMIT
This is the distance from where acceptable focus starts, when you focus at a given distance, whether that distance is the Hyperfocal or not.

FAR FOCUS LIMIT
This is the distance where acceptable focus ends, when you focus at a given distance, whether that distance is the Hyperfocal or not.

DEPTH OF FIELD
The distance between the farthest and nearest points which are in focus

DOF = FF - NF
Where:
FF = Far Focus Limit (millimeters)
NF = Near Focus Limit (millimeters)

So, if I'm reading this correctly, your DOF when focused at the hyperfocal begins at half the distance from the camera to the hyperfocal and extends to infinity. And when focused at the near focus limit begins at the NF and continues to the FF....which could be larger than the Hyperfocal DOF in some cases. (Clear as mud?)

Message edited by author 2007-07-31 20:31:40.

jrdawson

Canon EOS-350D Rebel XT

07/31/2007 08:32:38 PM · #5

Yeah, if you play with the numbers a bit, it seems that any 'far limit' over 10,000 feet gets changed to infinity.

Try 1853 feet and 1854 feet as subject distance values and you'll see.

Tamron SP AF 17-50mm f/2.8 Di II LD Aspherical (IF) for Nikon

07/31/2007 08:37:41 PM · #6

Originally posted by KaDi:

DOF when focused at the near focus limit begins at the NF and continues to the FF....which could be larger than the Hyperfocal DOF in some cases. (Clear as mud?)

Kadi, the term "near focus limit" and "far focus limit" mean that once you select a focus point, items between those distances will be sharp. They have no meaning until you focus somewhere, so you can't "focus at the near focus limit."

Tamron SP AF 17-50mm f/2.8 Di II LD Aspherical (IF) for Nikon

07/31/2007 08:38:37 PM · #7

Originally posted by jrdawson:

Yeah, if you play with the numbers a bit, it seems that any 'far limit' over 10,000 feet gets changed to infinity.

Try 1853 feet and 1854 feet as subject distance values and you'll see.

Thanks. For me in this instance, I need infinity to be infinity, not 10,000 feet, because I have objects up to 3 miles away. But it's no sweat; the closest object will be further than the hyperfocal distance anyway.

I was mostly just curious what was up with the calculators.

07/31/2007 08:42:34 PM · #8

Originally posted by levyj413:

Originally posted by KaDi:
DOF when focused at the near focus limit begins at the NF and continues to the FF....which could be larger than the Hyperfocal DOF in some cases. (Clear as mud?)

Kadi, the term "near focus limit" and "far focus limit" mean that once you select a focus point, items between those distances will be sharp. They have no meaning until you focus somewhere, so you can't "focus at the near focus limit."

The calculation uses the Hyperfocal Distance to calculate NF:

NF = (H x D) / (H + (D - L))

Where:
NF = Near Focus Limit (millimeters)
H = Hyperfocal Distance (in millimeters, from above equation)
D = Distance at which the lens is focused
L = lens focal length (i.e. 24mm, 28mm, 35mm, 45)

Since you don't have to focus at the HD the NF can actually be nearer to the camera than 1/2 camera to HD point.

(And, therefore the Maximum DOF can be greater than the Hyperfocal DOF.)

Message edited by author 2007-07-31 20:44:03.

07/31/2007 08:46:38 PM · #9

Or my math could just be screwy...
;/

Tamron SP AF 17-50mm f/2.8 Di II LD Aspherical (IF) for Nikon

07/31/2007 08:55:08 PM · #10

Originally posted by KaDi:

Or my math could just be screwy...
;/

I really do appreciate your posting all of that. :)

I think that the hyperfocal distance is not the only distance at which the far focus limit is infinity, but rather, it's the closest such distance. Since the DOF then stretches from half the HD to infinity, the total DOF is infinite.

If you focus closer than the HD, the DOF is less than infinite. If you focus further than the HD, the far limit can't get any further, but the near limit does, so the DOF again gets smaller.

Thus, focusing at the HD gives you the greatest DOF.

kirbic

Canon EOS R5

Canon RF 24-70mm f/2.8 L IS

07/31/2007 09:00:34 PM · #11

Originally posted by KaDi:

...
(And, therefore the Maximum DOF can be greater than the Hyperfocal DOF.)

In theory, DOF *is* maximized at the hyperfocal distance. You can't increase it by focusing somewhere else. The real question is, what numbers do you use to calculate the hyperfocal distance?
Jeffrey, if you use *any* of the online calculators, keep in mind that the CoC that they assign is based on the very old number of 0.030mm (30Âµm) for 35mm film. Divide 0.030mm by 1.5 (your crop factor) and you get 0.020mm, which is what they are using for the D200. Problem is, it's too large, and if you focus where it tells you, objects at infinity will be slightly soft. Better to use 2 times the pixel pitch of your camera. The pixel pitch of the D200 is 6.1Âµm, so use 12Âµm (0.012mm). On the DOFMaster online calculator, do this by scrolling way to the bottom of the list, it will allow you to choose a specific number. If you do this for your example of 280mm @ f/5.6, you'll get a hyperfocal distance of 3790 feet. Try both, and see what you get. :-)

electrolost

Nikon D200

Nikon AF Nikkor 28-85mm 1:3.5-4.5

07/31/2007 09:08:01 PM · #12

wow I think my brain is gonna explode

thegrandwazoo

Nikon D750

Nikon AF-S NIKKOR 24-70mm f/2.8G ED

07/31/2007 09:11:39 PM · #13

Originally posted by electrolost:

wow I think my brain is gonna explode

Yeah Fritz can do that to ya! :-D

07/31/2007 09:34:56 PM · #14

Originally posted by levyj413:

Originally posted by KaDi:
Or my math could just be screwy...
;/

I really do appreciate your posting all of that. :)

And I appreciate your raising the question...it got me thinking again. :)

If your mind isn't benumbed yet, there's a couple of good articles here:
Understanding the relationship between Maximum DOF and hyperfocal distance(alternate title misleading, content good)

What is HD and why should I care? (I like the explanation of when not to use HD. And also be sure to see the gadget for the Technically Obsessed!)