Focusing in The Digital Era Part Two

[Jack Varney]

The picture of the brick buildings does not appear to my eyes to have been focused at infinity. To me the second or third building seem sharpest. Perhaps the infinity mark was set to the f/16 mark or perhaps my syes are not so good.

Gary could you please clarify?

[Gary Ferguson]

Jack, no the camera was focused at infinity. Maybe because there's simply more detail resolved a little nearer it looks like focus was less than infinity?

[Tim Gray]

Would the "focus on infinity" theory work with 200mm @ 2.8?

For instance, in this specific example - which was 200mm 2.8.



In the demonstration picture in the article, why would you not have simply focussed on the building rather than infinity?  What's the magic of infinity?

I confess I've tried to read the Merklinger article a couple of times, but never "got it".

FWIW I think the problem is that some folks tend to treat DOF as binary "acceptable" = yes or no.  I simply view it as an analog continuum.  

You focus on what you want sharp (not the empty middle space between the sign and the building), decide if front to back sharpeness is important, and if so reconcile yourself to a compromise between diffraction, out of focus, and realistic shutter speeds.

[Rob C]

Would the "focus on infinity" theory work with 200mm @ 2.8?

For instance, in this specific example - which was 200mm 2.8.



In the demonstration picture in the article, why would you not have simply focussed on the building rather than infinity?  What's the magic of infinity?

I confess I've tried to read the Merklinger article a couple of times, but never "got it".

FWIW I think the problem is that some folks tend to treat DOF as binary "acceptable" = yes or no.  I simply view it as an analog continuum.   

You focus on what you want sharp (not the empty middle space between the sign and the building), decide if front to back sharpeness is important, and if so reconcile yourself to a compromise between diffraction, out of focus, and realistic shutter speeds.
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Hi Tim

'You focus on what you want sharp...' I think that you have stated the bottom line: it was ever so and for much photographic work not a great problem.

It seems to me that many people who get involved in landscape photography buy into a very old aesthetic - the everything sharp from front to back - school of thought. Now, why should that be required fact; is there a tablet of stone somewhere  that says so?

Look at much advertising imagery and you will see very clever use of differential focus, a tool that seems to pass many landscape photographers by.  An out-of-focus flower, shrub or whatever can be used to CREATE a sense of depth, never mind easing the self-imposed ordeals of chasing the impossible in optical law!

I was taught very long ago to treat depth of field as imaginary; there is only one, wafer-thin slice of life that is critically sharp and the rest less so to taste. Apart from the fact that seeing pictures printed at different magnifications gives them greater or lesser strengths and weaknesses, there is also the usual subject of viewing distance. So, do you decide what's acceptable by smelling the print or by looking at it at a reasonable walking-past-it distance? And this viewing distance, of course, has a direct bearing on the earlier decision about personal ideas of acceptability in DOF.

Some Saturdays are like this...

Ciao - Rob C

[Gary Ferguson]

Would the "focus on infinity" theory work with 200mm @ 2.8?

I doubt it, anything in the shot less than about 65mm wide would not be resolved! If your personal style is to utilise a limited depth of field then nothing in my article or Harold Merklinger's article will have any relevance to your photography. And that's okay, it was written for those photographers who have taken a different but equally legitimate path, and want front to back sharpness.

[howiesmith]

The article discusses "focus at infinty."  It states:

"What Harold Merklinger did was throw away the traditional focusing approach based on optical theories of circles of confusion, instead he developed a method that concentrates on resolving real objects within the scene. "

This same effect migh be achieved by increasing the hyperfocl distance by decreasing the circle of confusion.

H = F**2/(f*c)
where H is the hyperfocal distance, F is the focal length, f is f/stop and c is the circle of confusion.  Reducing c is reducing what the print designer calls in focus.  This requires a greater H.  So, "focus at infinty" is moving the hyperfocal distance back and focusing there.  Make c zero, H becomes infinity.

[tgphoto]

I took a look at Helicon Filter, and was wondering if anybody knows if a similar product exists for those redheaded stepchildren of us who use Macs?

[Gary Ferguson]

Timothy, I use a Mac and Helicon Focus works find with my "Tiger" OS.

[tgphoto]

Timothy, I use a Mac and Helicon Focus works find with my "Tiger" OS.
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My bad!  I was trying download Helicon Filter, which is Win only.  Downloading Focus now...thanks!

[AdrianW]

A free (GPL) focus stacking option:
CombineZ5

No idea whether it works, I've only recently started exploring the subject myself and haven't shot any test stacks yet...

[Jack Varney]

Jack, no the camera was focused at infinity. Maybe because there's simply more detail resolved a little nearer it looks like focus was less than infinity?
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Thanks, Gary. I think that must be the answer. Good article that will be helpful, BTW.

[jpoll]

I've used the CombineZ5 program for several years to increase the DOF of microscope images and have been impressed.  The Helicon Focus program does use masks which can certainly be useful in cases where some of the frames contain extremely out-of-focus components causing a bleed into the in-focus frames but the CombineZ5 program also has numerous parameter adjustments that can be made if you wish to deviate from the defaults to further correct a difficult image.  For a free program I definitely can't complain (although in the world of microscope imaging software even the Helicon Focus software could be considered inexpensive).  There are other free programs that use similar algorithms but I found the majority of them run slowly whereas the CombineZ5 program while not instantaneous is quick enough.  Recognize that the viewable frame dimensions will change slightly between images and you will occasionally have to crop two of the edges.

Joel

[gritmarques]

Hi, Gary,

Great article ...

A couple of  questions :

1.  "Now any object in the scene larger than 3mm will be identifiable, provided it’s within the resolution capabilities of the lens and sensor. So even though you’re focused on infinity, a 3mm wide blade of grass in the immediate foreground will still be distinguishable as a discreet and distinct object"

The size of the object you are referring to is the size of the object in the actual scene, and not the size as seen through the viewfinder, am I correct ?  Thanks.

2.  In your example picture of the brick homes with the sign, if I pointed the lens at the sign, all settings the same, will it come out sharp (being only 2 meters away), and still resolve the bricks well in the background ?

Thanks

[norfindel]

Hello,

I readed the article "Focusing in The Digital Era Part Two", which mentions the Merklinger method of Infinity Focus.
At least to me, Merklinger's Book (The INs and OUTs of Focus, available at http://www.trenholm.org/hmmerk/download.html) is confusing, so i decided to do a search in google about Merklinger's method, and found this article: http://www.hobbymaker.narod.ru/English/Art...arpness_eng.htm . It's a long article, but seems well done, and the photographs speak by themselves.
The most interesting paragraph to me is the following (next to fig. 12 in the article):

"The graph in Fig. 12 shows the degree of unsharpness as a function of the distance from the camera. The red curve corresponds to the case when a lens in focused at the hyperfocal distance (h), while the blue curve represents the lens focused at infinity.

As we can see from this graph, if any important objects are closer to the camera than two hyperfocal distances (2h), we should focus our lens at the hyperfocal distance. If all our objects are located behind this point, the focus should be set at infinity."

What do you think?

[Jonathan Wienke]

I think that statement is wrong-headed. As long as objects at infinity are acceptably well-focused, then there is no advantage to be gained by shooting at actual infinity, at least when there is anything in-frame that is not at infinity. I use the sensor pixel pitch as my CoC, and calculate DoF from there. This works very well for digital images, for predicitng what is in focus and not in focus when viewing the image at 100%.

[bobrobert x]

Late last year Colin Prior, a well known Scottish landscape photographer, rubbished the theory of hyperfocal focusing in a national magazine. His method was to focus on infinity and "crank"  ( his word not mine ) up the aperture till he gets the depth of field that he wants. I think that a lot of people will be rethinking their methods after reading what a world renowned photographer does in practise

[Tim Gray]

I think that a lot of people will be rethinking their methods after reading what a world renowned photographer does in practise
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then again, maybe not...

[norfindel]

I use the sensor pixel pitch as my CoC, and calculate DoF from there. This works very well for digital images, for predicitng what is in focus and not in focus when viewing the image at 100%.
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I think you're right. Using the pixel pitch as the CoC, guarantees the biggest area in critical focus. Maybe it's somewhat overkill to use exactly the pixel pitch, but how to be sure of the biggest safe value?

Naturally, as the cameras get more megapixels, this area will diminish, but that's ok. If you want absolute critical focus at the limit of what the camera can give, and you change your camera for one with more resolving power, this is going to happen.

The problem was the determination of the original CoC to be 0.03 mm. The Canon 300D has a pixel pitch of 0.007 mm, clearly, if one uses the original CoC, the same point of light will be replicated on a diameter of 0.03 / 0.007 = 4.2 pixels!!!  .

[BJL]

... if any important objects are closer to the camera than two hyperfocal distances (2h), we should focus our lens at the hyperfocal distance. If all our objects are located behind this point, the focus should be set at infinity."

What do you think?
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I think it would work at least as well to focus at a hyperfocal distance computed with a "pixel based" CoC value, like CoC equal to photo-site diagonal length, which seems to be about the resolution limit for standard CFA sensors. I do see the point in not using a hyperfocal distance based on the lower resolution standard of traditional DOF scales with CoC many times the typical modern pixel size.

What about a variant of another traditional approach: determine the distance to the closest subject that you want sharp, focus at about twice the distance to that subject, and try to stop down enough to get the OOF effects on this nearest subject down to the resolution limit of the sensor. I believe that this gives roughly equal OOF effects for objects at that minimum distance as for objects "at infinity", and less everywhere in between.


But maybe in most situations, that "pixel based" CoC gives a hyperfocal distance so close to infinity that the difference is not worth fussing about, so focusing at infinity is good enough for practical purposes. After all, such sharpness concerns arise mostly in the realm of seeking adequate DOF by using fairly small apertures.

[Jonathan Wienke]

The problem was the determination of the original CoC to be 0.03 mm. The Canon 300D has a pixel pitch of 0.007 mm, clearly, if one uses the original CoC, the same point of light will be replicated on a diameter of 0.03 / 0.007 = 4.2 pixels!!!  .

That is exactly why using traditional film-based CoC values when shooting digital is kinda retarded. Not too many people will accept the notion that a >4-pixel blur is actually "in focus". And yes, the more megapixels your camera has, the more restricted your DoF becomes. As the pixel count goes up and limits overall resolution less, it becomes easier to notice slight focus errors. What passes for "in focus" with a 3MP digicam is revealed to be out of focus when you switch to the 11MP camera.