Rabu, 18 Februari 2015

Hyperfocal distance - achieving maximum focus in landscape photography

From time to time I receive emails from readers asking pertinent questions about aspects of photography and/or equipment. When I receive one, like this question from reader David, that is probably relevant to many readers, I will make a blog post of my response where I can also add more details. 

Here is David's question:

"My aim is to use the 18-55mm kit lens with the majority of shots taken at the widest end.  I have in mind setting the lens at Hyperfocal distances, based on a crop factor of 1.5 and a circle of confusion of 0.02. I think the first figure is reliable, but I'm not sure about the second in relation to the X-E1 - perhaps you could confirm.

I have already done some testing at home using the attached table (which come from the well respected DOFmaster site).

In my experiment I carefully medewinared distances at apertures of f8 and f11 using a tripod and a printed card as the subject.  I set the lens manually at the hyperfocal distance, using the EVF distance scale. I was disappointed to find that the closest point of focus was not as sharp as I had hoped.  Have you any idea why this may be? 

I did a further test on aperture f11 and this time set the distance scale at 4 feet (2/3 of the way between 3 and 5 feet).  This resulted in a sharp image from 3.5 feet.  This would suggest that the distance scale is not accurate.

Any suggestions you have to overcome the problem would be much appreciated."

Using the extreme depth-of-field by using the hyperfocal distance may not be the most desirable way to achieve what you want. It is often better to come to an understanding of what you want in the scene and work from there. In this image the point of focus was placed on a specific area, the foreground grass, and the background was allowed to drift imperceptibly out of focus. We don't notice this because the sharpness of the foreground detail keeps us thinking that everything is in focus. Had the reverse focus been used with the camera set to infinity for the background mountains, the image would have lost detail in the foreground where it is most noticeable.  This photo was taken at f/11 with a 35mm lens on a Nikon D3X. 
For anyone who might not know what it is, the hyperfocal distance is the focus distance point in a scene that will achieve the maximum over-all focus for the scene at a given lens aperture for the particular lens you are using. The key word here is "maximum". This is not saying that "everything" will be in focus. There is a big difference. Much of the ultimate focus results will depend upon -- and differ -- with the focal length and aperture you use.

At one time all lenses had a depth-of-field scale printed right on them so the photographer would know exactly what was in focus for any given aperture. In this example of a Leica 28mm Summicron lens the focus is set at about 7', and the depth-of-field (DOF) scale indicates that with an aperture of f/11 everything from 4' to infinity will be in focus. The maximum DOF of this lens would be achieved at f/16 and the DOF indicator placed so that the infinity mark is at 16. We can then read the point of focus and the distance closest to the lens that will also be in focus. 
A problem shooting digital lenses is that they do not perform at their best when stopped way down into the f/16 and small range. It is much better in terms of resolution to use the lens at its sweet-spot of around f/5.6 or f/8. This makes achieving a complete focus from foreground to background very difficult. 

I prefer to use work-around solutions to achieve the same effect. 

First, you can use a tilt-shift mechanism with a Nikon lens on the Fuji X. There is one available for the Fuji XF mount. I discussed in a previous blog post here. (You can purchase it here on Amazon.) Of course, this presupposes you have a Nikon lens of the desired focal length available. Not the most practical solution. 

Actually, hyperfocal distance, or what I will call "aparent hyperfocal distance" is dependent more on the level of sharpness we consider to be acceptable. This brings me to the second work-around, which is the most practical:

Rather than simply try to get everything in focus, try narrowing your own mental focus about what is important in the scene and achieve a primary focus on that allowing the rest of the scene to go a bit softer. This is the method I, and many other landscape photographers, often use. It works well on several accounts. First, it forces you to make a decision on what is important in the scene and zero in on it. Second, it allows you to place the focus point closer to the foreground where you can achieve complete foreground focus of the elements in the scene that most benefit from sharp focus. Finally, you are allowing the background scene to go slightly soft, but that is the area with the least actual detail anyway. Plus its softness may not even be noticeable because of the magicians slight-of-and trick to distract your audience into looking at the foreground detail. Let's look at a couple of samples below.

Two variation where the camera was moved in close to foreground scene and focused on an important story-telling detail that leaves the entire background drifting slightly out of focus. The viewers doesn't really notice the lack of sharpness in the background because their attention is distracted to concentrate on the detail in foreground.
In this scene and the one below, focus is placed on important foreground detail and the distant background is allowed to drift to a slight softness. The images appear to be sharp over-all, but in reality they are not. 


If you are really determined to achieve a photo with everything in focus, then you might want to consider this third, alternative approach of a stacked-focus image. To do this, you take a series of photographs while moving the focus point slightly backward with each exposure until you have covered the entire area from front to back. Later the images are assembled with a program like Helicon Focus into a final image where the entire scene is in focus. The final results can be a mind-blowing experience for viewers because we rarely see real life this sharp. The image below is an example of stacked focus.

Over twenty photos were taken to form this image. Each exposure was focused at a slightly different point moving progressively from front to back. All were later assembled to form on over-all sharp image. Click here to download a high res version of this photo. 
Bottom line here is that it more important for the photographer to come to a decision about what is the most important element in a scene and then judiciously relate that area to the whole by using depth-of-field, as opposed to randomly selecting a hyperfocal distance that bears no meaning in and of itself other than achieving a deep focus. As always, it is the photographers aesthetic decisions that are most important in any photograph.  


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