Category: Focus

Post related to all aspects of focus in photography

What is manual focus in photography?

Manual focus

Most modern cameras, including smartphones, have auto focus systems, whereby the camera in various ways automatically selects the focus of the image. It can be a face or a point in the frame selected by the photographer. Manual focus is when you as a photographer bypass the options for automation of the focus and manually choose to focus the lens yourself. The benefits is more control and more freedom to decide the outcome, but it also introduces potential for errors in the shape of out of focus images that were not intended to be out of focus.

The switch for changing from auto focus to manual focus sits on the lens in this case.

In the image above (the Nikon 70-200) there is a switch on the lens that allows you to choose between manual focus (the rightmost option M) and two different flavors of auto focus. When in manual focus, you as a photographer have to turn the focus ring (the rubberized ring top left in the image) to obtain focus.

The Nikon D700 has a switch on the camera body to engage and disengage the auto focus motor sitting on the camera body.

In other cases, typically for older lenses without a focus motor built into the lens and hence dependent on a motor in the camera body, the switch to engage or disengage the auto focus sits on the camera body. I the image above you can switch between continuous auto focus (C), single auto focus (S) and manual focus (M).

When you focus manually, you move the focal plane closer to and further from the camera by turning the focus ring on the lens. You can think of this as a big vertical plate that you push back and forth as you turn the focus ring. All the things the plate “touches” will be in focus. Things just before and just after the focal plane will appear to be in focus as well, subject to the depth of field.

When you focus manually, the camera will typically give you some help to determine if you have the focus that you want. The classic way of doing this is with a small indicator that has to arrows and a focus confirmation dot:

Credit: Nikon D700 manual

With mirrorless systems you also have so called focus peaking highlights, that based on contrast shows you which parts of the frame that are in focus. It does so with a color you can select; in the example below the color is red (notice: there is nothing naturally red in the frame as such – all red is added to the image by the camera as part of helping you obtain focus):

The focus point is the red box in the top of the frame a little to the right of the middle. You can move this point around, typically using either a command wheel or a joystick on the camera. The image above is from the rear LCD of the camera, but the focus point is also visible in the viewfinder, both for DSLRs and mirrorless cameras.

If you look very carefully, bottom left in the LCS, just to the right of the battery indicator, there is an arrow pointing to the right. This tells you that the focal plane needs to be pushed a bit further away to obtain focus in the selected focus point.

Focus confirmation dot is active. 

In the image above, the focal plane has been pushed a bit further away, and you now see that the focus indicator to the right of the battery indicator shows the round dot that is the signal for focus + the focus point top right in the frame has turned green – another way of showing that this point is in focus.

All of the above may sound a bit overwhelming, but I assure you that it is much simpler when you try it out in real life and see how the moving parts work together.

The benefits of manual focus is control. You’re the boss. Often automated systems do not do exactly as you want them to, although it constantly gets better and better with face recognition and other forms of intelligence in the cameras. However, there still are situations where manual focus for some is the preferred way to go, and I recommend that you try it out to see what it can do for you, to decide if it should be part of your photography “arsenal” or you instead want to go for relying on the cameras automatic systems.

Further reading

What is focus shift?

What is focus breathing?

What is focus stacking in photography?

Focus stacking

Focus stacking is a post processing technique where several images of the same subject and scene is combined in post processing, to make all of the image sharp rather than having the sharpness defined by the depth of field.

Focus stacking is especially useful for macro photographers, because the depth of field becomes very very shallow when the lens focuses extremely close to the subject, but also landscape photographers and architecture photographers can benefit from focus stacking.

Example

Look at the silly picture below, taken in my office. In the foreground and in focus you have the mad cow and in the background and out of focus, my glasses, a computer screen and a lamp with a bright light.

Below a picture of exactly the same scene. Nothing has changed, other than the focus has been moved from the foreground, the cow, to the background, my glasses. Notice how blurred the cow in the foreground is.

The trick is now to combine the two so that you pick the parts that are sharp and use these in a combined picture. You can do this in post processing software like Photoshop. I open the two images as layers in photoshop.

First step is to make sure the pictures sit right on top of each other, and Photoshop has a function to secure this (edit, auto-align layers).

Second step is to ask Photoshop to create masks to combine the two images into one (edit, auto-blend layers, stack images). You can see in the two images below how the top one selects the cow, whereas the bottom one selects large parts of the background including the glasses. What is white is included and what is black is masked out.

The resulting image is shown below. As you can see, both the cow and the glasses are now sharp, which is exactly what focus stacking can do for you: it makes it possible to have both objects very close to you and objects very far away appear sharp in the image.

If you study the image carefully, you will notice that the lamp looks a bit funny. It is as if the edge between the light and the dark part suddenly has a half circle to the left – just above the head of the cow. This is due to focus breathing – the lens used here suffers from slight focus breathing, meaning that the angle of view changes ever so slightly when the focus changes. This error makes it impossible for Photoshop to combine the images properly as the size of the lamp varies between the two images. So it is important that there is absolutely no focus breathing for lenses used for focus stacking!

Related reading

What is focus breathing?

What is Depth-Of-Field?

What is focus shift?

When your DSLR focuses, it typically does so by opening the aperture up as much as possible to allow all the available light to flow to the auto focus system. So if for example you are shooting with a f/1.8 lens at f/8, the camera will open up to f/1.8 to focus and then shift down to f/8 to take the picture.

Some lenses, especially lenses that can go very wide, i.e. a low f-stop number, suffer from focus shift, which means that the lens moves the focal plane as a consequence of changing the aperture.

This is nothing short of a catastrophe for an auto focus system, as the camera gets the focus sharp at f/1.8, but then when the image is taken at f/8 the subject is no longer in tac sharp focus.

There are a few ways to mitigate focus shift, as you can of course shoot at the maximum aperture – then the focus aperture and the shoot aperture is one and the same. You can also shoot in live view on your DSLR, as it the uses a different focus system than when not shooting in live view mode. The best option of course is to get a lens that does not suffer from focus shift!

What is the circle of confusion?

Short not-too-technical definition of the circle of confusion.

Lets say that a dot in reality is represented by a dot in your picture.  Your eyes and brain in combination will form an opinion about how well the picture shows the dot, and if it is in focus or not. The shape and the size of the dot is the deciding factor.

Here is the thing: Your evaluation is not binary! In other words, you don’t make a “flip a switch” assessment, rather you accept some minor deviations in the way the dot is shown in your image. Sometimes the dot is spot on (he-he) and other times it is a bit oval or a bit larger that the real thing.

The interval in which you accept the dot to be sharp is known as the circle of confusion. Don’t ask me how this term came about, but the point is that accept small variations and still think of it as sharp.

It is the circle of confusion that gives us depth of field! The fact that minor variations in how the dot in reality is represented in the picture, gives us some wiggle room before and after the focus plane and this is exactly the DoF. Without a circle of confusion there would be no DoF!

Related reading

What is aperture? And why important?

What is Depth-Of-Field?

What is lens distortion?

What is focus breathing?

When you zoom in and zoom out you expect the effect to be a change in angle of view, i.e. that the subject moves closer to you or further away.

When you turn the focus ring on your lens, you expect the lens to move the focal plane back and forth to focus on different subjects in the frame.

Focus breathing is when your lens does both at the same time! As you turn the focus ring the angle of view changes as well. In other words, the closer to yourself you zoom, the shorter your lens becomes! For example the Nikon 70-200mm f/2.8 is actually a 120mm when it focuses to minimum focus distance at 200mm!

Focus breathing is for most of us not an issue, but in two cases it can cause you a headache:

  • In a scene where you have two persons in the frame talking to each other and you want to focus back and forth between the two as they speak, you really don’t want to change the angle of view. It needs to be constant, otherwise the viewer gets confused at best, and a bit seasick at worst. You want that framing to be constant. For this reason, videographers absolutely do not like focus breathing.
  • Macro photographers struggle with focus breathing when doing image stacking, that aims to compensate for a very shallow DOF by blending images that have been shot of the same subject with varying focus points. Here you absolutely need the framing and angle of view to be constant, otherwise the image will look very strange or at worst your post processing software wont be able to blend the images.

So should you worry about focus breathing? Not really, if you ask me. Only in the two above specific cases would I worry.

Of course it can be annoying to know that your wonderful lens has focus breathing, but now that you know what it is and in which cases it is a problem, in all other cases you can disregard focus breathing.

Thank you for reading this far! Comments and questions more than welcome!

What is hyperfocal distance?

The hyped distance…

Although the name sounds very advanced and almost like something from a galaxy far far away, it is really very simple: to make the most of your dept-of-field (DOF).

Notice the “distance” in the term “hyperfocal distance” – it is all about the distance between your camera and the focus point. When you focus at the hyperfocal distance, everything between that point and to infinity is in focus. Or I should say, appears to be in focus. There is a lot of technical details here that I omit, but I want to give you a drivers license to shooting at the hyperfocal distance – not turn you into an engineer.

Your depth-of-field (DOF) is an interval before and after the focus point where things appear to be in focus. I normally think about it so that 1/3 of the depth-of-field (DOF) lies before the focus point, and 2/3rds lies after the focus point. This is not very accurate, but a good operational way to think about it. So when your focus point is so that the far end of the DOF just reaches infinity, then there is also a good part before the focus point that is in focus. If your hyperfocal distance for example is 10 meters away, then the space between the focus point and halfway back to you also appears to be in focus. In other words, only what is between you and 5 meters out will be out of focus. From 5 meters out and to infinity is in focus.

Calculations are not necessary

So should you calculate the (DOF)? You can if you want to, but what I do is to focus to infinity with manual focus, and then pull the focus point back towards me until infinity becomes out of focus, and then revert just a little bit until infinity becomes sharp again, and then I have the focus point hyper focal distance. If you have a mirrorless camera with focus peak highlights, this is a brilliant illustration of how your focus plane and the (DOF) works you can find the hyper focal distance using the method I just described, but supported by the focus peaking highlights.

Learning from old lenses…

On old lenses, there was markings showing the (DOF). The black dot just above the blue “11” shows that the lens is at f/11 aperture . The same blue color as the “11” is used for the (DOF) markings on the zoom ring. You can see that to the left, the blue mark is at infinity, and to the right the other blue mark is between 3 and 5, i.e. around 4, the precision is not that great. The focus point is between 5 meters and infinity (the tilted 8 to the left just above the black dot). The blue mark to the left is the far end of the (DOF) whereas the blue mark to the right is the near end of the (DOF).

DOF indicator on the Nikkor 50mm f/1.2
DOF indicator on the Nikkor 50mm f/1.2

Is the lens at the hyper focal distance? Yes, it is as the far end of the DOF touches infinity. Had I focused closer, then infinity would be out of focus (which every portrait photographer knows), had I focused further away, I would have wasted DOF beyond infinity.

The distance is not linear

Also notice the distance scale: You can see it (in meters) top right is at 1.2 meters, then 1.5, 2, 3, 5 and infinity! So it is almost is if the distance “explodes” when you get beyond 5 meters, i.e. a very small turn on the focus ring gives a big jump in the distance. That is why it is vital that you get the far end of the DOF to touch infinity, because you then work with the part of the distance scale where you cover a lot of ground!

DOF calculator

If you put the above example into a DOF calculator (credit: Photopills) then you will get a hyperfocal distance of 7.42 meters, DOF near limit to the half of that and the DOF far limit to infinity. In this example we have got the most out of the DOF and only the distance from the camera and 3.7 meters out is out of focus.

DOF calculator from Photopills
DOF calculator from Photopills

Notice that the DOF depends on several factors, such as the sensor size, the aperture you shoot at, the focal length of your lens, distance to the subject etc. But no matter what DOF you are working with, the hyperfocal distance is the focus distance where you make the most of what you got.

Related reading

What is manual focus in photography?

What is the focal plane in photography?

 

What is the focal plane in photography?

In this short blog I will give a non-scientific layman terms explanation of how I see the focal plane in photography. You can find more technical and advanced explanations out there, but this one focuses on what you need to know to make use of the focal plane.

A big umbrella

The focal plane is the plane where your lens and camera in combination has your subject in focus. So when you zoom in and out, different things will appear sharp in your viewfinder. If you take a picture of a person, you risk that the eyes are out of focus if you focus on the ears or the nose. Eyes are super important in portrait photography, and hence all portrait photographers and advanced auto focus systems make sure to zoom in on and detect the eyes. It is less of a problem if the nose or ear is slightly blurred or out of focus.

You can think of the focal plane as one big virtual umbrella that you push back and forth as you turn the focus ring on your lens. Exactly where the fabric from the umbrella touches the subject, the subject will be sharp.

In the picture below, you can see the glasses that I have put in focus are almost the only thing in focus. Both before and after the glasses, everything is out of focus:

Only one focal plane

It is important to understand that there is only one focal plane. No matter how advanced a camera you have and how much intelligence there is in the auto focus system of your camera, the physics and mechanics do not change. There is only one focal plane. You can only push one “umbrella” back and forth. You can do this with auto focus or manual focus, but there is only one.

I say this because when you see or read some of the camera manufacturers adds for the latest and greatest in auto focus technology, you get the impression that the intelligent systems have overcome all focus and sharpness issues. They have not, because they cannot fundamentally change the fact that only one plane can be in focus at a time.

There is some good news…

The good news – and what has saved me a lot of times – is that a little before and some after the focal plane, there is an additional area where the subject appears to be sharp. This is known as the depth of field. Good news is that you can increase (or decrease) the depth of field if you change the aperture. A small aperture (large f-stop number) gives large depth of field. In other words, there is some room for slack if you have a small aperture (large f-stop number like f/16) .

There is no such thing as a free lunch in photography. So the price for a small aperture is that it lets in very little light, which means you need to bump up either the ISO or leave the shutter open for a longer time or both. This introduces the risk of camera shake and subject blur, meaning your pictures will appear not-so-sharp anyway. So you have to strike a balance, find a compromise. General advice is hard to give in this regard, but try to start out with a middle-of-the-road aperture (say f/5.6) and work your way up or down until you find a good compromise.

Depth of field is also depends on your distance to the subject, so the closer you are to your subject, the more shallow the depth of field will be in absolute terms. This is what causes a lot of headache for for example flower photographers. This is where focus stacking comes into play, but that is the subject for a different blog.

Questions and comments

Thank you for reading this far. I hope you found this blog useful. Questions and comments (and likes!) are more than welcome!