Hi René,
René Damkot wrote in post #3141718
Sorry, I don't agree: I prefer to focus on infinity.
Click Harold M.Merklinger’s article, "Depth of Field Revisited," as seen at the link you provided, is an overview of a focusing method Merklinger details in his out-of-print book, "The INs and OUTs of Focus". He is generally regarded to be the originator of the idea that focusing at Infinity can offer some benefits over focusing at the hyperfocal distance when the subject space includes objects at Infinity in addition to objects that are closer than Infinity.
A free PDF edition of Merklinger's book can be downloaded here: "The INs and OUTs of Focus".
Many people who read this book somehow come away with the conviction that focusing at Infinity yields a superior (or at least an equivalent) image quality to that had when focusing at the hyperfocal distance. This is not the case. You have to read the entire book to understand that Merklinger is only pitching his "focus at Infinity" method as a convenient way to avoid the effort required to focus at the hyperfocal distance, BUT Merklinger makes it clear that this convenience is had at the expense of image quality (in foreground sharpness), or at the expense of shutter speed, or both.
You can find evidence that despite his having invented this idea of just focusing at Infinity, Merklinger understands that there is useful DoF beyond the plane of sharpest focus (when you focus at Infinity, you are not making use of the very precious DoF available beyond where you've focused) -AND- he understands that CoC diameters can be made small enough to produce sharp images while hyperfocusing (you don't have to treat CoC diameters as a constant and be disatisfied with the results had when hyperfocusing). His book does not at all dismiss the fact that hyperfocusing really can produce sharp images. Best of all, his book proves that HE KNOWS his focus at Infinity technique produces compromised images. Stay with me...
Consider his Rule of Thumb #6 (page 37): "The zone of acceptable delineation of the subject falls equally in front of and behind the point of exact focus (not 1/3, 2/3!)."
Which prompts me to ask this question: Why would you want to throw away the "acceptable delineation of the subject" that's available BEYOND the plane of focus when focusing at Infinity? Hold that thought as we continue...
Or his Rule of Thumb #20 (page 71): "The usual depth-of-field scale is calculated for a 1/30 mm circle-of-confusion. Typical 35 mm films and lenses are capable of delivering a 1/150 mm standard. To convert an existing depth-of-field scale to a new (higher, more demanding) standard, all we have to do is multiply the numbers on the depth-of-field scale by the improvement factor we desire. To go for that five-fold possible improvement, multiply all the numbers by 5: Instead of f/2, read f/10. Alternatively, divide the f-number you are actually using by 5 and look for that spot on the existing depth-of-field scale: if you are using f/11, look for the f/2.2 depth-of-field mark. And, if you wish, you can use different standards for the far limit of depth-of-field and for the near limit."
That last sentence from his Rule of Thumb #20 reveals that Merklinger acknowledges that DoF calculations can be tailored to be as aggressive as we need them - by choosing a Circle of Confusion diameter that smartly accommodates the anticipated enlargement factor and viewing distance.
But you can also find statements like this:
From page 21: "In general, I have found the results obtained using the time-honored methods usually yield backgrounds which are on the fuzzy side."
Here's where he begins to get silly in an effort to sell his novel focusing method. I have to ask the question: Is he pretending there's only one CoC diameter we can use for hyperfocusing? If not, there's no excuse for fuzzy backgrounds when using "time-honored methods!" (See his Rule of Thumb #20!)
Rule of Thumb #4 (page 36): "If we want anything at infinity to be critically sharp, focus at Infinity."
That doesn't jive with Rule of Thumb #6! Why would you focus at Infinity if "The zone of ACCEPTABLE delineation of the subject falls equally in front of and behind the point of exact focus?" If you find the DoF in the foreground produces acceptably small CoC's (or disks of confusion, as Merklinger calls them), why wouldn't these same sized CoC's be acceptable beyond the plane of exact focus - in the background?
And his Rule of Thumb #23 (page 72): "A gentle repeat reminder: when you focus at the hyperfocal distance, you are guaranteeing that subjects in the distance will be resolved no better than your specified minimum standard. In order to improve upon this, you must focus beyond the hyperfocal distance."
Here he suggests the possibility that we can use a standard of our own choosing - "your specified minimum standard" (a la Rule #20) - but when he suggests that we focus beyond the hyperfocal distance to improve the sharpness of distant subjects, he NEGLECTS to mention a critical point: If our chosen standard were aggressive enough to begin with (if we had smaller CoC's), we wouldn't feel moved to sacrifice foreground sharpness just to obtain acceptable background sharpness!
And in his Summary, Chapter 11 (page 73): "The traditional depth-of-field philosophy usually ends with the advice: to maximize depth-of-field, choose a moderately small lens opening, set the focus to the hyperfocal distance, and shoot. My parting advice would be a little different. For typical normal and wide-angle lenses, especially lenses having focal lengths less than about 50 mm no matter what the camera format, set the lens opening to somewhere in the 2 mm to 5 mm range, set the focus at infinity, and shoot. For lens openings larger than 5 mm, and for longer lenses that tends to mean all normal working f-stops, focus on what is critically important."
Focusing at infinity can not be done without forfeiting the DoF that resides beyond the plane of focus (Merklinger's Rule # 6!), thus the aperture you must chose to adequately resolve foreground subjects when focusing at Infinity will be smaller than that which could be used if hyperfocusing instead! Merklinger chooses not to stop down that far and thus suffers UNSHARP foregrounds. Where does he say that? Keep reading...
Under a photograph of a church with flowers very near in the foreground (page 60), he writes: "Taken with a 28 mm lens at f/11, infinity focus provided all the depth-of-field necessary."
Without question, if he's content with the CoC diameters in the foreground subjects, he could have hyperfocused and been just as content with his infinity subjects at something like f/8 (where the DoF that resides beyond the plane of focus could have been pressed into service instead of wasted!)
And on page 68: "Since working out these details, I find I do a lot of photography with the lens simply focused at infinity."
How convenient! But don't miss this: Merklinger admits that the convenience comes at a price...
From page 22: "Objects photographed up close can still be recognized even if they are a little fuzzy. Objects in the distance may need to be very sharply imaged if they are to be recognized at all."
From page 48, under the infamous cannon and village picture: "The cannon, the grass, the gravel, and the trees are clearly a bit fuzzy, but we have no difficulty in recognizing them." You've got to laugh at that: "clearly a bit fuzzy".
From page 66: "Experimenting, I learned that with the lens focused at infinity, things up close still seemed to be adequately sharp."
So Merklinger admits that his infinity focus method produces foregrounds that are "a bit fuzzy", "a little fuzzy" or "seemed to be adequately sharp."
Merklinger's method is clearly a compromise that is acceptable only if you are willing to suffer "fuzzy" foregrounds in favor of sharp Infinity subjects and a very convenient way to set focus and select aperture. The fact remains that everything in the shot can be made at least as sharp as his Nears at a wider aperture (faster shutter speed) than he's using - by focusing more closely than at Infinity. And, despite his negative comments about hyperfocal focusing, his own Rules #6 and #20 reveal that he knows one can achieve acceptably sharp Nears AND Fars by hyperfocusing for a smaller CoC diameter.
Merklinger's method boils down to this: If you're willing to take a hit in foreground sharpness and waste the DoF that lies beyond the plane of focus, you can put convenience ahead of quality by focusing at Infinity and selecting an aperture that's just small enough to make foreground subjects only "recognizable". If you want the convenience of focusing at Infinity AND the foreground sharpness had when hyperfocal focusing, you'll have to stop down further than you would with hyperfocal focusing (because you're throwing away all the DoF that lies beyond the plane of sharpest focus), suffer the slower shutter speed that comes with using the smaller aperture, and increase your risk of inducing visible degradation due to diffraction across the entire image.
No thanks! I'll stick with using depth of field calculations that have been customised with a smartly chosen CoC diameter - per the formula documented in Wikipedia's article on Circle of Confusion.
The half a minute required to use a depth of field calculator will not only tell me at what distance to focus, but will also give me the widest aperture (and therefore, the fastest shutter speed) capable of delivering the CoC diameters necessary to support my desired print resolution for an anticipated enlargement factor and viewing distance.
Mike Davis
http://www.AccessZ.com
