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Hyperfocal Distance and Focusing

What is it good for?

Hyperfocal focusing, or focusing at the hyperfocal distance, allows you to maximise your Depth of Field (DOF) and position the Near and Far Limits of your DOF so that all or part of the scene that you are photographing is acceptably sharp.

The Short and Sweet:

If you focus at the hyperfocal distance, then the image will be in focus for half the hyperfocal distance all the way to infinity. For example, if your hyperfocal distance is 5 m, then as long as your focal point is at 5 m from where you stand, your scene will be sharp all the way from 2.5 m to infinity. This is particularly useful in landscape photography, where you often want as much of the scene as possible to appear sharp. You can calculate the focal length and aperture setting for a particular hyperfocal distance with this downloadable hyperfocal chart.

Tell me more:

The hyperfocal distance is quite sensitive, since if you focus only slightly nearer than the hyperfocal distance, then the background in your image can appear too soft. As mentioned in our discussion of DOF , the sharpness of your image falls off with distance from your focal point and is just about acceptable at the Near and Far Limits. If the part of your image that is close to the Near or Far Limit needs to be particularly sharp, you may want to consider focusing at those points and blend the images taken at different focal points.

Depth of Field

What is it good for?

The Depth of Field (DOF) is a crucial concept for controlling the part of your image that appears sharp and in focus.

The short and sweet:

Any discussion of DOF has to include two essential points. Note that the DOF is always defined w.r.t your focal point(s):

1) The DOF distance. This is the distance in the scene you photograph which appears acceptably sharp in the final image. Lets say your DOF is 2 m, then the part of your scene that is acceptably sharp will be the 2 m around your focal point.

2) The portion of the DOF distance which extends in front of and behind the focal point, which also may be referred to as Near Limit  and Far Limit.

Several DOF calculators are available online and you can even download apps for your smartphone.

 The calculations take into account several factors, including:

1) Aperture

2) The distance of your subject from you, i.e. focal point

3) Focal Length

 

An illustration of the central concepts of DOF for an image with acceptable sharpness from foreground to background. Note that the DOF here extends actually extends to infinity, but I decided to indicate the Far Limit as being at the horizon.

 

Tell me more:

You will notice that we used the term “acceptably sharp”. This is because the only part of your image that is close to perfectly sharp is that at your focal point.The remainder is blurry but if the blurriness falls below a certain amount, called the maximum circle of confusion, it will not be perceptible to the viewer. This “circle of confusion” depends on two factors, which fall under the discussion of the DOF, and are thus included as points 4 -6.

4) Camera Sensor Size

5) The final size of the displayed/printed image and the distance you are viewing it from.

6) The eye sight of the viewer.

The Near and Far Limits of your DOF are those points where the circle of confusion has reached the maximum size for acceptable sharpness. There thus always is a gradual increase in blurriness (or size of the circle of confusion) as you move away from your focal point.

For other, detailed discussions of DOF please follow this link.

What is Aperture and Why Should I Care?

A camera’s aperture is the opening through which light, after it has traveled through your camera’s lens, enters the camera body.

The size of your aperture determines:

1)The time it takes for you to expose your image properly

2) The Depth of Field (DOF) of your image, which is the extent to which your image is sharp around the point at which you have focused with your lens.

3) The sharpness of your image, and the ideal aperture size for sharpness depends on the lens you are using.

The aperture size is regulated by a diaphragm, much the same way the eye’s iris functions. One should therefore speak of the effective aperture size.

The opening of the aperture is expressed in terms of an f-number. To calculate the f-number, one takes the ratio of the diameter of the aperture opening  to the focal length used. For example, if the focal length of your lens is set at 100 mm, and the diameter of your aperture opening is 25 mm, then the f-number for the aperture is f/4 since 25 mm/100 mm = 1/4. If you reduce your aperture opening to 12.5 mm, but keep the focal length at 100 mm, then the corresponding f number would be f/8, since 12.5 mm/100 mm = 1/8. For the same focal length, an increase in f-number,e.g. from f/4 to f/8, thus corresponds to a decrease in the aperture opening. Alternatively, if your aperture is at f/4 but you change your focal length from 100 mm to 200 mm then the opening of the aperture increases from 25 mm to 50 mm.

From the figure below, you will note that the f-numbers increase by factors of 1.4.  The area of the aperture is proportional to the square of its opening,and thus a change by a factor of  1.4 in its opening corresponds to a change of 1.4² = 2 in its area. Each step in the f-number is called an f-stop. If you increase the f-number by one stop, e..g from f/1.4 to f/2,then you are halving the amount of light that enters the camera – this is also called stopping down. This is also where the term f-stop comes from – one stop corresponds to a factor 2 change in the amount of light that enters your camera, and this also corresponds to one exposure value (EV).

 

 

Besides controlling the amount of light that enters your camera, the aperture opening is critical to the Depth of Field (DOF) of your image. The smaller the aperture, the greater the DOF and the less blurry your image is around your focal point. However, this can negatively influence the sharpness of your image (not related to DOF), due to an optical effect called diffraction. For each lens, there is a so-called sweet spot aperture opening, where the image is the sharpest. If your aperture is larger than that, the sharpness is negatively affected by aberration effects. If it is smaller than that, the sharpness is negatively affected by diffraction effects.

The ideal aperture for most lenses unfortunately allows for a rather shallow depth of field. However, nowadays one can still achieve  almost perfect DOF for rather large aperture openings by being able to blend a series of images taken at different focal points.

 

For more detailed information, please visit  http://en.wikipedia.org/wiki/Aperture

 

 

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Nikon D800 vs Canon 5D Mark III – Choosing an advanced SLR

Well, after some extensive research I finally have purchased a new camera . My trusty Canon 5D now is more than 6 years old and besides the fact that, after a few hard falls, it is about to draw its last breath, there is also some amazing technology out there which greatly expands what is doable and opens up a whole world of creative opportunities.

For me, one of the most important developments is the ability to shoot relatively clean images at very high ISO (film sensitivity), something which would have been unthinkable 5 years ago. This has resulted in a surge of night photography where spectacular images of the milky way abound. The sensitivity of the sensors is so high, and the noise so low, that taking high ISO images for as little as 10 s reveals detail not visible to the eye. In addition, a 10 s exposure is short enough for the motion of the stars to be imperceptible – no more need for star trails!

As concerns reasonably affordable cameras for the serious amateur or professional, there are two frontrunners in my opinion: The Nikon D800 and the Canon 5D MK III.

Nikon originally priced their D800 at $ 3000 as compared to the $ 3500 5D MK III. The price for the MK III has now dropped to around $ 3000. The D800 boasts a substantially higher pixel count, 36 MP vs 22 MP, thus catapulting it into the domain of medium format cameras. Its high dynamic range (the amount of separation between highlights and shadows it can capture without blacking out the shadows or blowing out the highlights) is comparable to the MKIII, it has very good high ISO performance, only slightly less than the MKIII, and it excels in shadow noise (the amount by which one can boost the exposure in the shadows in postprocessing without introducing excessive noise). In addition, the best ultrawide lens out there is the Nikon 14-24 and when used with a Canon, the automatic functions such as exposure and focus do not work.

So I chose the D800, right?

The D800 is too slow for my purposes. I like to shoot wildlife and I am constantly adding to my adventure portfolio. This often requires shooting many frames at as high a rate as possible. The relevant technical citeria for this would be the burst rate (the maximum number of frames per second), the number of frames until the camera’s buffer is full, the burst rate when the buffer is full, and, very importantly, the time it takes for the files to be written to the memory card and the buffer to clear out. It is in the two latter criteria where the MKIII truly excels: The time for files to be written to memory is 4s for the MKIII compared to 21 s, and the frame rate at full buffer is 2.7/s continously while that of the D800 is 1/s for 3 shots before one has to wait another 0.9s to repeat. For full details, please see the test results for the MKIII and the D800. I have often been in situtations where I had to wait several seconds before I could shoot again at the full rate, and by that time the scene I wanted to capture would already be over.

Choosing between the D800 and MKIII was not easy, but the MK III clinched the speed category by a long shot. The reduced price helped too!

You can find reviews for the MK III here and its sensor here.

For the D 800 see here and the review focused on its sensor, see here.

 

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Exposure Blending Part I

In this post, I will write about what I feel is one of the main strengths of digital photography: Exposure blending. As we know, the digital sensor/photographic film can capture both shadow and highlight detail as long as the range in exposure values falls within its dynamic range. In cases such as sunrises or sunsets, with the sun included, this is almost never possible. In those cases, if exposing for the sun, shadows will be blacked out and detail lost, while exposing for the shadows, the sun will be blown out.

Although a significant number of digital and, by implication, film camera users, swear on Neutral density gradient filters (NDGs), I prefer exposure blending in most cases, since I feel it gives the photographer a much richer tool set for technical perfection and creative outlet.

I prefer exposure blending for two reasons:

1) Mind the line: No transition lines/obviously darkened areas of the image. Although NDGs keep exposure in check, in tricky scenes, which arise surprisingly often, the NDG line (the border between coated and uncoated regions of the filter) may be obvious in the final image. This is especially so for hard stop NDGs. These lines can be very hard and time consuming, if not impossible, to remove in post processing. Alternatively, you would have to be very skilled, since such lines could be avoided with 2 or 3 carefully arranged NDG’s, a time consuming effort. With exposure blending one can carefully combine exposures that were taken. One only needs to use the proper masks (which will be a topic of future posts). I manually blend my images and avoid the HDR approach, which in my opinion is seriously lacking, especially for landscapes.

2) Chase the light: With transition lines no longer a worry, you can now follow rapidly changing light conditions from different vantage points and with varying compositions, and still end up with technically excellent images. You won’t loose out on precious seconds of beautiful light as you fidget around with filters. You only need to ensure that the highlights and shadows are captured in correctly bracketed exposures, which can easily be checked with the exposure histograms on your camera LCD. The uninitiated will be pleasantly surprised by how rapid and simple this procedure is.

The two images below illustrate particularly tricky scenes which I was able to capture within a matter of seconds, allowing me to move on to the next subject/composition, and still come away with technically sound images. This would have been very difficult and lengthy, if not impossible, to achieve with NDGs, unless I was happy with some fat transition line through my work.

Canon 5D, Canon EF17-40 mm f/4L @ 17 mm, 1/30 s, 1/8 s and 0.5 s @ f/22, ISO 50.

The image above was taken on the frozen shores of Lake Ontario, Canada. This scene had a rather high dynamic range, from shadows within the “ice cave” to strong highlights associated with the rising sun and the bright snow. Had I used a NDG to keep the sky and shadows in check, a transition line likely would have passed through the top of the cave and/or part of the frozen lake surface. Instead, I took three exposures to capture the dynamic range, and then was able to blend these images with suitable masks in a way which I felt best reflected the scene as I remembered it.

Canon 5D, Canon EF 17-40 mm f/4L @ 23 mm, f/20 @ 1/50 and 1/13 s, ISO 50.

The second image, above, is an image of High Falls on the East Side of Algonquin Provincial Park in Ontario, Canada. This scene exhibited an extreme dynamic range, since it was taken in the late afternoon when the sun was still strong, and a number of areas in the image were in deep afternoon shadows. In this case, a strong NDG filter would have put parts of the trees on the top of the waterfall in deep shadow and artificially darkened the sky, just to keep the sun in check. The transition from the lighter bottom part of the trees to the darker top part would have been particularly obvious. In this image I blended only two exposures, but had to double process one exposure and tripple process the other. Although it was a lot of work, it certainly was worth it!

There are however cases where blending exposures may not be the best approach. When bracketing for exposure, images are taken at different points in time. This is problematic if there are areas of the image which incorporate moving objects and which need to be blended. Typical examples would be moving clouds or water; even a lake’s shimmering surface would be a case in point. For this a NDG comes out tops, since the exposure is kept in check in one single shot.

A strength of the NDG that is often overlooked, is the fact that it reduces flare in the camera. By flare I do not mean the obvious streaks or lines that are introduced, but the more subtle aspect of light bouncing around in the lens, thereby reducing contrast and sometimes seemingly changing the color temperature of the scene – light will appear a lot warmer than what it actually was. This can happen even if the sun is not included in the scene. The photographer will place the darker areas of the NDG over the brighter region of the sky and thereby will reduce the total amount of light hitting the lens, reducing flare. With exposure bracketing one needs to be particularly careful, since when one exposes for the shadows a large amount of light from the brighter part of the scene will enter the lens and thereby introduce flare, even in the shadows! One should shade the lens from the brighter part of the sky with one’s hand (flare caps as supplied by lens manufacturers are in my opinion quite useless), and then blend accordingly. If there is flare, the effect of blocking out the light can easily be seen in the view finder. The image below is an example where I used my hand to block out the sun when exposing for the shadows.

The image above is a view, taken in later afternoon, of islands surrounding the Greek Island Amorgos, which forms part of the Cyclades in the Mediterranean. This also is a blended exposure. However, when exposing for the foreground, a significant amount of light from the setting sun entered the lens and introduced flare throughout the image. This killed the contrast necessary to convey the beautiful golden glow on the foreground shrubs. By shielding the lens from the sun (this meant my hand was blocking the top part of the image), I eliminated flare, and by blending with an exposure for the sky and sun I was able to realize this image. In future posts I will describe in detail how this image came about.

That’s all for this post. In the next series of posts I will give some examples of manual blending, mask generation and will introduce the reader to an extremely powerful tool, luminosity masks.

 

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