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Hyperfocal distances and Merklinger's method in landscape photography
This article describes and compares two different methods for
optimizing depth-of-field in traditional landscape photography, where
both near and distant objects are expected to be in reasonable
focus. The use of hyerfocal distance has the benefit of long usage,
and is well-understood. Merklinger's method is less widely used,
but is much easier to apply in the field.
In this article I've assumed a basic familiarity with photographic
concepts such as aperture, exposure, and focus. I haven't presented
any of the mathematical analysis, only the results, because the
math is well-established and easy to find elsewhere on the Web.
The problem stated
The problem, in essence, is to find camera settings — lens selection, aperture, etc. — that will allow both
near and distant objects to be in focus. To have
objects sharp over a wide distance range is often desirable in
landscape photography, because subjects close to the camera
give a sense of depth and scale to the image, which might be
lacking if the whole scene is distant.
The diagram below shows a typical situation, and one that will be
used to illustrate the rest of this article.
A common approach to photographing this kind scene is to focus on the distant
mountains — which are usually "at infinity" so far as photography is
concerned, and hope that the foreground will take care of itself. If
one uses a small-ish aperture — f/8 or smaller — and a wide-ish angle
lens, very often everything will work out fine (see below for
an explanation why this is). However, having the
nearest subject at only 5m from the camera is a challenge with this
The classic depth-of-field problem in landscape photography: how to
set the aperture and focus distance such that the foreground objects
and the very distant objects are both still in acceptable focus?
The traditional best-practice method for dealing with the challenge
illustrated above is to make use of hyperfocal distance. Hyperfocal
distance is defined in two, somewhat related ways; both will be important
in the discussion that follows, so I will quote both.
Hyperfocal distance is the closet point at which, if a lens is focused,
objects at infinity are acceptably sharp. When so focused,
the range of acceptable sharpness extends back from the focus distance
to a point half the focus distance from the camera (see the diagram below).
The first of these formulations of hyperfocal distance is the one
that most photographers know about, and is
Hyperfocal distance is the distance from the camera at which
objects just become acceptably sharp, when a lens is
focused at initity.
There are a few points to note about hyperfocal distance.
being sloppy when using terms like "distance from the camera". It's
reasonable to ask what part of the camera; but for landscape photography
where the scene depth runs to miles, this isn't a significant objection.
Second, these two definitions give distances which differ only by a focal
length and, again, that difference is irrelevant in landscape work.
Third, it's reasonable to ask what "acceptable focus" means. A lens
has at best one plane of perfect focus — only objects at one
exact horizontal distance from the lens axis can ever be truly in focus.
The uncertainty in how to specify acceptable focus
leads to significant contention, and is a point that I will take up again
Fourth, the point of focus is a surprisingly short distance into the
scene. It strikes many photographers as counter-intuitive
that, in a scene where
distant objects may be miles away, the hyperfocal method tells them
to set the focus at, say, ten metres. The diagram above does not really
show how peculiar this sitation really is, because I can't draw it
to scale. No other diagram I've seen of hyperfocal distance does
any better — there's an intractable problem of scale here. But
the hyperfocal distance really is generally as short as the math
tells us it is.
Fifth, and this is a direct consequence of the previous point,
the distant objects are typically at the far boundary of the zone
of acceptable focus. Your distant mountains will just be sharp,
according to the definition of sharpness you've adopted (see below).
The point of best focus is, of course, the hyperfocal distance and,
very likely, there's nothing in particular of interest at that
distance. That's just a statistical matter — if your scene extends
from (say) five metres to five miles, odds are that there's nothing
much going on at the exact point of focus.
When comparing with Merklinger's method, this last point is particularly
significant, because Merklinger would have us focus on the distant
objects, which will therefore be at the point of best focus.
The hyperfocal method generally offers sharpest focus in the
foreground regions of the scene. More on this, somewhat controverial,
Hyperfocal distance as it is traditionally employed in landscape
photography — focusing at the hyperfocal distance ensures a
depth-of-field from half the hyperfocal distance to infinity
The hyperfocal 'circle of confusion'
The hyperfocal method turns on being able to define what "acceptable focus"
means. Only objects at one distance (broadly) are in perfect focus;
everything else will be out of focus, to some extent. The notion of
circle of confusion is an attempt to objectify the subjective notion
of acceptable focus. The circle of confusion is (broadly) how close two
features can be, before they can no longer be resolved as separate features.
This is, in principle, an objective measure because it depends on the
resolution of the film emulsion or digital sensor. However, in modern
practice these resolutions are generally higher than the resolution of the
human eye, when frames are printed at common sizes. Therefore, most
photographers have adopted a conventional circle of confusion of 0.02mm, which
is derived from the resolving ability of the human eye when looking at
a regular print at arm's length. Many computer programs or smartphone apps
that provide hyperfocal calculations purport to be able to use a
circle of confusion that is tailored to a specific camera; but how
they can do that with no knowledge of how the images will be post-processed
and presented, I really couldn't say. The conventional figure of 0.02mm is
pretty arbitrary, to be honest, but it is well established. All the
calculations used in this article are based on this figure.
For the record, hyperfocal distance is calculated using the following
where H is the hyperfocal distance, l is the focal length
of the lens, c is the circle of confusion, and f is
the f-number (5.6, 8, 11...). Be aware that if you specify the focal
length in millimetres, the hyperfocal distance will also be in millimetres.
Note that the '+l' term in this expression may usually be ommitted
as it is small, and
it is this small term that forms the (small) difference between the two
different definitions of hyperfocal distance I gave earlier.
There are similar expressions for working out the nearest and furthest
points of focus, but I'm not going to give them, as they are well-known — just do a Web search for 'depth of field formulae.'
H = ( l2 / (c f) ) + l
Harold Merklinger describes his method for optimizing depth of
So far as this article is concerned, his method for dealing with
scenes that extend to infinity (or, at least, for miles) can be expressed
When this method is applied, I will refer to the aperture selected
as the Merklinger aperture for simplicity. I should point
out that Merklinger's treatise deals with more situations than
simply maximizing depth-of-field, and is mathematically rigorous.
Merklinger's method replaces the notion of 'circle of confusion' with
what he calls a 'disk of confusion'. The difference is that Merklinger
is concerned with features in the world, rather than in the
resulting image. A disk of confusion is no less arbitrary than a circle of
confusion, and does not have the benefit of fifty years of practical
experience to back up the conventional values used. In principle the
disk of confusion does not depend on the way that the image is post-processed
and displayed, provided that the resolution of the camera sensor, printer,
etc., are adequate (and they probably are with modern equipment).
In practice, images are often displayed at less than life-size, and
a feature that could be resolved in life might only be resolved using
a magnifying glass in a printed image. So there is a risk that the
method might be too conservative — that it might force the use of a
smaller aperture than is really needed. However, as I will show,
in practice this does not seem to be the case, at least with
values of disk of confusion commonly used.
In practice, photographers using Merklinger's method seem to have settled
on a disk of confusion of 5mm-6mm, rather as many who use hyperfocal
distance have settled on a circle of confusion of 0.02mm. 6mm is sufficient
to distinguish individual blades of grass, or two facial moles from
one another, or texture lines in a rock. However, if the nearest subject
is very close, setting a lower value of disk of confusion might be
The tables below show the aperture that needs to be
set for two different disks of confusion values: 2mm-4mm and 5mm-6mm.
The reason there are ranges here is because in practice
we can't set an arbitrary f-stop: we're limited to the values provided
by lens and camera manufacturers. Consequently, it doesn't make
any difference whether the disk of confusion adopted is 5mm or 6mm — the
calculated apperture rounds up to the same f-stop (we need to round
the f-number up, rather than down, because we want to err on the side
of a smaller aperature and increased depth of field. Probably.)
Merklinger's method for scenes with distant objects
Focus on the most distant object in the scene, and set an aperture
whose diameter is equivalent to the disk of confusion. The
disk of confusion is the smallest distance between objects in the
scene that need to be resolved.
Lens focal length
Nearest point of acceptable focus
Merklinger's aperture for a disk of confusion of 5mm-6mm, for various
lens focal lengths. With this aperture, and the lens focused at infinity,
then features 5mm or larger will be distinguishable. The nearest
point of acceptable focus according to the conventional depth-of-field
formula is shown for comparison.
These tables tell us, for example, that if we want to use a 27mm lens,
and will accept a 6mm disk of confusion,
then we should set f/5.6 (or smaller aperture) and focus at infinity.
Conventional depth-of-field formulae tell us that the point of
nearest acceptable focus is 4m at this point. We can't find out the
point of nearest focus using Merklinger's method, but we can
determine that features at least as large as 6mm will be resolvable.
An interesting, and coincindental, feature of the 6mm disk of
confusion is that the point of nearest focus is, within a metre,
the same as the f-number. So in a sense, Merklinger's method
does give us a way to estimate the point of nearest focus. Sadly,
there's no simple correspondence (that I could find) between f-number
and the near point with any other disk of confusion. However, I've
point of nearest focus easily enough because it is by definition
the same as the hyperfocal distance with the lens focused at
infinity (see Definition 1 above.)
Merklinger's method is extremely simple to apply in the field — you don't need to calculate anything, you just need to remember a handful
of numbers. If you're content to work with a 5mm-6mm disk of confusion,
you just have to remember one f-number for each lens: f/4 for 18mm,
f/5.6 for 27mm, f/8 for 35mm, f/11 for 50mm, and so on. Of course
you can use an aperture smaller than any of these, so long as
Lens focal length
Nearest point of acceptable focus
Merklinger's aperture for a disk of confusion of 2mm-4mm, for various
lens focal lengths. With this aperture, and the lens focused at infinity,
then features 2mm (or so) or larger will be distinguishable. The nearest
point of acceptable focus according to the conventional depth-of-field
formula is shown for comparison.
lens focal lengths are the real focal lengths, not SLR-equivalent
focal lengths. Broadly, a 35mm lens on a camera with an APC-S sensor will
have an angle of view roughly the same as a 50mm lens on a full-frame
sensor. This fact is completely irrelevant to Merklinger's method — we
use the focal length engraved on the lens.
With the 6mm disk of confusion value, we need also to remember not
to have in the scene anything closer in metres than the f-number; again,
this is an easy rule of thumb to remember.
Hyperfocal and Merklinger compared in practice
If we focus at the hyperfocal distance, then objects at infinity
will always (just) be in focus. So with the hyperfocal method
we need to consider particularly how
the near point (point of closest focus) varies with aperture.
This is illustrated for a range of lens focal lengths in the
With this method, even with the closest object in the scene only
5m away, most lenses will offer a range of apertures that will
keep the whole scene sharp. In fact, any lens with a focal length
up to 35mm will be sharp from about 5m to infinity with any
aperture setting f/5.6 or smaller.
How does this compare with the Merklinger method? Using the 6mm disk
of confusion value, looking at the table above we see that we should
focus at infinity, and set an aperture of f/4 for the 18mm lens,
f/5.6 for the 27mm, and f/8 for the 35mm. Using the hyperfocal distance,
these settings give near focus points of 4m, 6.5m, and 7.7m respectively.
With this method, only the 18mm lens will put the 5m object in the
zone of focus. However, the other lenses only put the near point
a few metres away, which might matter little in practice — since
we don't know how comparable the circle of confusion and disk of confusion
What the hyperfocal method gives us, however, is the knowledge that we
could open up to f/2.8 with the 18mm lens, rather than the f/4 offered
by Merklinger, and still have the 5m object in the focus zone.
So, arguably, the hyperfocal method gives is a bit of extra flexibility
where keeping near objects sharp is concerned. This is hardly a surprise — we would be focusing only 10m-20m into the scene with this method.
Focusing with the Merklinger method is trivial — in practice we
focus (automatically or manually) on the most distant point of the scene,
or just set manual focus to the infinity stop, or as near as the
lens will get to it. Focusing on distant objects, rather than infinity,
is probably a little better in landscape work, because this will
tend to move the near point a bit closer to the camera. In practice,
however, it's unlikely to make a discernable distance.
Focusing at the hyperfocal length, however, is a different matter,
particularly if your lens does not have a distance scale, or the
scale is not particularly precise (not unusual). It's worth thinking
about how the near and far focus points will be affected by errors in
focus. As an example, for the 35mm lens at f/5.6, the following
graphs show the variation in near and far points. The
vertical dotted line in each graph shows the hyperfocal point — the place we ought to be focusing.
This graph shows how the point of nearest focus varies with
apperture, when focused at the hyperfocal distance, for various
lens focal lengths. Notice that to be sharp at 5m, an aperture
of f/8 will suffice for any of the lenses. However, the 18mm
lens should be sharp from about 5m to infinity for any
aperture setting. It's hard to take an out-of-focus landscape shot
with lens if you set the focus manually to something reasonably
close to the hyperfocal distance (which, of course, varies with
aperture). For all other lenses, more care is required
The near point varies only slightly with focus distance — in fact it
varies less than the focus distance error in this case: focusing
five metres too far into the scene only moves the near point one metre
away. However, the far point is a different story. Focusing too
far into the scene does not move the far point back (as it is already
at infinity), but focusing too close has a dramatic effect on
the far point. Focusing even one metre too close reduces the
far point from infinity to only about 100m. This could well
ruin the shot. Most likely your lens or camera will not allow focus
to be manually set with a precision of one metre, so you'd have
to compensate for this error (as photographers generally do).
One stop down (smaller aperture) will nearly always fix the problem
with far point when
focus distance is uncertain, and will bring the near point closer, too.
But this won't help when the lens is already fully stopped down, or there
isn't enough light to stop down further. In addition, some lenses will lose
sharpness owing to diffraction at smaller aperture than f/11 or so.
The Merklinger method is unaffected by focus position errors, because
focus and the far point are always at infinity.
Because there is no long-standing convention about how to choose
the disk of confusion in Merklinger's method, it's interesting to
see how the near focus point varies as different values are chosen.
Because the Merklinger method always has sharp focus at infinity,
we don't need to consider the far point. The results for a 27mm
lens are shown below.
How the nearest and furthest points of focus vary with
focus point, with aperture f/5.6 and a 35mm lens. The hyperfocal
distance with this configuration is 10.98m (dashed vertical line).
The crucial point here is how rapidly the far point collapses
if the lens is focused too close: focusing even at 10m (about
1m too close) reduces the far point to 100m
As we might expect, the larger we choose the disk of confusion, and
thus the larger the aperture, the near point moves further away and
depth-of-field decreases. The relationship between near point and
disk of confusion is a linear one so, although choosing 'wrongly'
will affect which near objects are sharp (as it should) it won't
affect it disproportionately, in the way that focus position errors
do with the far point using the hyperfocal method.
It's worth bearing in mind that a disk of confusion of 1mm is probably
not achievable with any common lens — common lenses won't stop down
to 1mm diameter.
How the near point varies with the chosen disk of confusion in
Merklinger's method. This graph is for a 27mm lens and,
although the gradient of the line is different for other lenses,
it is always a straight line.
"f/8 and be there"
It's worth wondering how much any of this complexity is actually
necessary. Suppose we just set f/8 and focus at infinity? Of course
distant objects will be sharp, so we need to consider only
the near point.
This combination, f/8-infinity, will produce good results for a
range of lens focal lengths, and very good results for
wide-angle lenses, and requires no calculation or even a lot of thinking.
What's more, the f/8 aperture is likely to correspond to a workable
shutter speed in a whole range of lighting conditions in a way
that f/16, for example, won't.
What we have to be careful not to do, in landscape work at least,
is to set f/8 and focus on the nearest object in the scene, if
that object is only 5m away. We'll get away with it with lenses
27mm or shorter; but for 35mm and up the far point will be less
than 30m away.
With aperture at f/8 and focus at infinity, objects as
close as 16m are sharp, with any lens up to 50mm.
For more wide-angle lenses, the near point is even closer
The key difference between the hyperfocal and Merklinger
methods is that the hyperfocal method
tends to emphasise sharp focus for near objects, whilst Merklinger
favours distant objects. Since we have chosen a circle of confusion or
disk of confusion, the methods should, in principle, produce comparable
focus results, because in both cases both near and far objects will
be 'in focus'
within the criteria chosen of in-focus-ness. However, because we can't
focus exactly at a particular point (hyperfocal method), and because
we don't really have much experience of choosing a disk of
confusion (Merklinger method), the near/far object distinction may
well be relevant in the field.
So which to use? As always, it depends on the circumstances.
In the end the choice of method might come down to
a simple question: which is more important — confidence in close focus or
confidence in distant focus? In practice, in landscape photography
distant objects are often unsharp anyway, owing to atmospheric
haze. Close objects, however, are usual capable of sharp focus.
In really demanding situations, where the nearest subject is only a few
metres from the camera, then there's probably no alternative to
using the hyperfocal distance calculation. This is particularly
true if the foreground is clear and well lit, and the background
dark or hazy. However, some care needs to be taken to ensure that
you don't set the focus point too close. In most other situations,
Merklinger's method is likely to produce perfectly decent results,
with a whole lot less math.
- Setting f/8 and focusing on the most distant object in the
scene will produce acceptable
depth of field for most lenses commonly used in landscape
photography. It requires
no calculation or even much thinking, and will suit a range of
different lighting conditions. We have to be careful, however,
to focus on the most distant object and not some foreground subject
- Provided we don't obsess too much about the size of the disk of
confusion, and are happy with a working value of 5mm-6mm, then
Merklinger is trivially easy to apply. You don't need to make any
in-the-field calculations — just remember which Merklinger aperture
goes with which lens, and focus on the most distant object in the scene.
You can even use auto-focus, or just turn the manual focus ring to
- Merklinger's method will produce results at least as good as simply
setting f/8, although for some lenses the Merklinger method will,
in fact, tell you to use f/8 (see the various tables above.)
Merklinger might be better than simply setting f/8 because you might
be able to use a brigher aperture than f/8, which might be an advantage
in low light or low-ISO situations
- When using the hyperfocal method, it's advisable to calculate the
hyperfocal point for a particular f-stop, and then stop down one
position, as otherwise small errors in the focus position can have
dramatic effects on the far point. If you can't do that, it's better to
set the focus distance too long rather than too short as, although this
will affect the near point, the effect on the near point is
far less pronounced
- With Merklinger, distant objects will always be sharp, even if
errors are made in setting the aperture. With hyperfocal, near
objects will nearly always be sharp, even if errors are made in