Depth of Field and Hyperfocal Distance Scales on Irix Lenses

Not long after Irix lenses became available to photographers in the USA, we posted an article explaining the markings on our lenses for Depth of Field and Hyperfocal Distance. It also explained how to use both scales without much emphasis on why. 

In this article, we'll revisit those features, how to use them, and how they can help you create more engaging photos. We will also provide some examples to demonstrate how effective they can be as creative tools.

Coming to Terms with the Terms

Most readers will understand the term "depth of field (DOF)." Hyperfocal distance may seem more complex, but we're hoping to show you in this article that it's only complicated if you actually need to "do the math”, and with Irix lenses, there's no need for that.

Let's take an in-depth look at these two optical phenomena (without the physics lesson) and how they relate to each other, as well as what each can do for your photos.

What is Depth of Field?

Before we can define DOF, it's important to understand the meaning of "focus" from two different perspectives:

1. From an objective point of view, it describes the sharpness of an element or elements in an image. An object is said to be in focus if the edges and details are clearly defined.
2. When considering the overall image, an object within the frame can be emphasized to draw viewers to focus on it. That focal point can be created in various ways, and one of the most effective is to isolate, aka separate, the subject from the other elements with careful control of depth of field.

With that in mind, DOF can be defined as the distance between the closest element in focus and the furthest element in focus in an image. You can think of it as a band of sharpness between the camera and infinity or the most distant object in view. That band can move toward or away from the camera and grow larger or smaller, depending on several factors, which we'll explain in a moment.

Focus Limits

The beginning and end of the band are defined by a Near Focus Limit and a Far Focus Limit, the distances at which the sharpness of objects starts to become unacceptable.

It's also important to know that sharpness increases or decreases gradually around each end of the band, rather than abruptly. Focus, therefore, is progressive within the image, instead of having a sharply defined beginning or end.

NOTE: Don't confuse the Near Focus Limit with the Minimum Focusing Distance of a lens. The latter is a lens specification that describes how far away an object needs to be from the focal plane of the camera, in order for that lens to bring it into focus. It will come into play, but it's a limiting factor that doesn't change, while the Close Focus Limit can.

Factors that Affect Depth of Field

Three major factors affect DOF, any and all of which we can use to control it in our images:

• The current aperture setting of the lens. The wider the aperture, the narrower the DoF
• The focal length of the lens, or the current focal length for a zoom lens. The longer the focal length, the shallower the depth of field.
• The camera-to-subject distance. More distance increases the depth of field.

There is a fourth factor, which is somewhat out of our control, known as the Circle of Confusion (CoC). While we won't go into detail about this, it has to do with imperfect focusing of light rays and it varies with camera sensor format. This means that the depth of field will change slightly when using a full-frame lens on a crop-sensor camera.

Irix Lens Focus and Depth of Field Scales

It's easy to see how determining the depth of field in a photo can be difficult without some sort of aid. The focus and depth of field scales on Irix lenses are the tools you need to establish the area and range of sharpness you want in your image.

The photo below shows the DOF scale on the Irix 15mm f2.4 Blackstone lens . We've added some graphics to help illustrate talking points. (Depending on the make of camera your lens is for, the scales may be reversed but will function the same way.)

For the moment, let's ignore the scale marked "hyperfocal." We'll be using that in a while. Just below that scale, you'll see markings that represent feet (ft) and meters (m). This is the focus scale and since we're in the US, we'll use feet in these examples. The large center mark on the stationary ring below the focus scale is the focus indicator. Note that it's currently aligned with the 8 ft mark on the focus ring, meaning that the lens is focused at a point 8 feet away from the focal plane of the camera.

We've marked the depth of field scale with a rectangle in the photo for convenience. The numbers to the left and right of the focus indicator represent aperture settings and will show you the Near Focus Limit and Far Focus Limit for a given aperture setting. For instance, looking at where the f/16 indicators align with the numbers on the focusing scale, you can see that the range of best focus will extend from about 3.2 feet to beyond infinity.

Now, remembering that a wider aperture will decrease the depth of field, you'll notice that the indicators for f/ll show a much narrower range of focus; about 4 ft almost to infinity. Finally, of course, the f/8 indicators show an even narrower range.

These two scales, when used together, provide a perfect example of the relationship between focusing distance, aperture setting and depth of field. And, of course, they're the perfect aid for visualizing the area of focus within a photo before it's taken.

A Few Examples

For a photographer, a picture is worth much more than a thousand words, so we're going to provide you some visual examples of how this DOF thing works. We'll be borrowing the following exercises from Irix Ambassador, Alberto Bouzón:

"On the table I have an element that I want to take a photo of and it is located 1 meter from me. I rotate the ring until the 1 meter mark is on the center focus line or mark. I press the shutter and wait for confirmation of focus. If everything is properly configured, a click should sound, which is one of the most important features that the Irix lens also has.

When taking the photo, and regardless of which aperture we have [selected for] the photo (regardless of the correct exposure or not), the element we have focused on must be perfectly in focus.

Now what happens if we have taken the photo at an aperture of f/2.4? Well, the main element is in focus, but the elements that are a little in front of the element or behind it are already out of focus. And this is because the depth of field is very small when using very wide diaphragms.

We are going to take the same photograph now. Without moving the focus ring, it stays at the 1 meter mark, but this time at f/11.

What do we observe now?

Well, the main element is in focus and the rest of the elements in front and behind also have an acceptable level of focus.

How far?

We look at the focus ring again and see that the main mark is above the 1 meter mark. We see that the mark on the left of f/11 drops almost 0.7m, and the mark on the right of f/11 is a little short of the 2 meter mark.

What does this mean?

Well, the depth of field in a photo of an element that is located 1 meter away, with the Irix 15 mm at f/11, ranges from 0.7 or 0.8 to almost 1.75 or 1.85 meters. We have a depth of field of approximately 100 centimeters.

What would happen if we took the photo at f/16?

Well, without looking at the marks, we can already assume that that depth of field is greater since we have closed the diaphragm more.

How much deeper is it now?

Now let's look at the f/16 marks, and we will see that the one on the left is closer than 0.7, and the one on the right is between 2 and 3 meters. That is to say, now the depth of field is almost around 200 centimeters. Almost 2 meters of depth of field gained by just closing the diaphragm 1 full stop.

And what about the diaphragms that are not marked?

The operation is similar. But, as the diaphragms open, the depth of field gets much smaller. There would not be much room for marking, and it would be difficult to establish those distances. Additionally, these wide-angle lenses are primarily used for landscapes with values ​​between f/8 and f/16. 

If you still want to know exactly the depth of field values ​​for any aperture and any distance from the main subject, you can use a series of tables or programs that make the exact calculations, taking into account the camera, the focal length, the aperture and the rest of the parameters in a personalized way."

We hope this explanation and the examples provided will help illustrate the concept of depth of field and the ease with which it can be established in your photos with Irix Lenses. Now, let's move on to that next term:

What is Hyperfocal Distance?

When it comes to maximizing the depth of field in a photo, hyperfocal distance is your best friend. In fact, that's exactly what it's for, and knowing how to use it is a blessing for landscape photography. We'll be showing you why in a bit, but first, let's define it in a way that's easy to understand.

The definition that best fits outdoor photography is "the distance from the camera where all objects beyond that point will be rendered at maximum sharpness." It's important to add that, like depth of field, the hyperfocal distance changes with the focal length or selected focal length of your lens and your aperture setting. (You already figured that out, didn't you?)

So to translate all of that into simple terms, hyperfocal distance is: The point where you should focus your lens to maximize the depth of field in a photo at a specific focal length and aperture setting. (There are other definitions and explanations, and the formulas for calculating it will make your head explode.)

There are tables and charts, and apps to help you calculate it. Many of us old-timers used our depth of field scales to determine the approximate setting. Fortunately, Irix has given all of us photographers a much simpler way!

The Hyperfocal Distance Scale

In the image below, we're again looking at the scales on the Irix 15mm Blackstone lens, this time focused at infinity. Now let's look at that top scale, marked "hyperfocal." (We would have given it the full name of "hyperfocal distance," but it would have taken up too much space.)

You'll notice there's a relationship here between the hyperfocal distance and the f-numbers on the depth of field scale, just as there is with the actual aperture settings. Now, let's rotate the focus ring until the number 16 on the hyperfocal scale aligns with the focus indicator:

This focuses the lens at the hyperfocal distance when you've set the aperture at f/16 with your camera's controls. At this setting, everything in the frame from half of this distance to infinity will be sharp. (In this case, about 5.8/2, or roughly 2.9 feet.)

As you can see, the correct focus is easily set for f/11 and f/8 in the same manner. There's no need to focus visually to make sure that you'll have the maximum depth of field in the photo you're about to take!

"So, why not just focus on a foreground element?" Remember that the farther away your focal point (subject) is, the greater the depth of field becomes. Focusing on an element too close to you may result in blurring in the midrange and background.

By using the hyperfocal scale on Irix lenses to set your point of focus for maximum depth of field at the aperture you're using, you can be sure your photo will have the maximum possible sharpness, which is exactly what you'll want in your landscape photos.

Alright, that's a lot of information to process. Let's use some diagrams, to help illustrate how all of this comes together.

Using the Irix Hyperfocal Distance Scale to Maximize DOF

Let's assume you're setting up to photograph a landscape that includes an ancient water well with flowers in the foreground, trees in the distance and a snow-capped mountain range on the horizon. Quite an idyllic setting for an amazing photo, right?

Shooting in Auto Mode

The average novice photographer might shoot a landscape like this in full autoexposure mode and use an autofocus point to focus on the well. Let's asssume the light's a little low, so the camera selects the widest aperture setting - let's say f/2.8 and a shutter speed to match. Here's what they result might look like:

Because the wide aperture shortened the depth of field, the band of focus is very narrow. The distance to the subject isn't far enough to expand that band, so with these settings, the well is nicely focused, but the narrow DOF blurs everything in front of and behind the well. The photo really doesn't do the scene justice.

Stopping Down

Now, let's assume you're not the average novice, and you've followed our blog posts for some time, so you know that you can increase the depth of field by stopping down the lens diaphragm. So, you switch the camera exposure mode to AV or A (Aperture Priority) and stop down to a nice, average aperture of f/8. Once again, you let the camera focus on the well, because that's your point of interest. Your result might look something like this:

The depth of field has increased, but not nearly enough. The flowers and trees are beginning to come into focus. The mountains, however, aren't anywhere close to sharp! You're a smart photographer, and remember that increasing the distance between the camera and the focal point increases the depth of field. Maybe you can fix the problem by focusing at infinity! You switch to manual focus and dial it in. Here's the result:

What happened? Well, the depth of field increased - a lot. However, remember that infinity isn't a tangible number. You've focused the lens to it's most distant point, and that band of sharpness has moved with it as it's expanded. So, where's the Far Focus Limit? Theoretically, it's off the chart. It's going to bring not only the mountains, but the sky and anything else behind it into focus. Pro tip: That's why focusing at infinity works so well for shooting the night sky!

Alright, so now let's consider what two different photographers might do to resolve this:

Photographer #1 grabs his cell phone and opens his favorite photography app; for instance he might use Photopills. He brings up the hyperfocal function and enters his the make and focal length of his lens and the aperture he's shooting at: f/8. The app gives him the hyperfocal distance and he carefully sets it as close as the markings on his lens will allow. (If he doesn't have manual focus or distance markings, he'll focus on something in the frame at the correct distance.)

Photographer #2 uses his Irix lens and aligns the 8 on the hyperfocal distance scale with the focus indicator.

After taking the shot, both photographers might see something like this:

Consistent with what you now know about hyperfocal distance, everything from half the hyperfocal distance out to infinity - as far as you can see - will be sharp. That's great depth of field, but it's not quite enough to bring all of those flowers in to focus. Looking back at the factors that control DOF, what choices are available to get the rest of those flowers in focus?

• Move the out of focus elements far enough away from the camera to be in focus. We don't recommend this option in this case, since digging up flowers is probably going to be frowned upon.
• Move back. Remember that increasing the distance between you and your subject increases depth of field. Moving back several steps might increase it enough to bring all the flowers into focus. Unfortunately, that also changes your framing and may or may not be convenient. In our example above, the photographer would fall off the edge of his world. Tragic, don't you think?
• Stop down. The simple and most practical solution is to decrease the aperture diameter by increasing the f-number. This will increase the depth of field and decrease the hyperfocal distance.

Photographer #1 stops down to f/16, recalculates the hyperfocal distance and refocuses at that distance by whatever means he needs to use to judge it.

Photographer #2 (We're hoping that's you) simply changes the aperture setting to f/16 using the camera controls and aligns the 16 on his hyperfocal distance scale with the focus indicator.

Here's how the final image looks:

As the diagram above shows, the change in aperture extended the depth of field and shortened the hyperfocal distance. By now, you should begin to see how DOF and hyperfocal distance affect your photos as well as how easy the scales on Irix lenses make using them.

Consider this: If you're photographer #2 in the above scenario, you would simply attach your Irix wide-angle lens and rotate the hyperfocal distance scale, checking the distances on the depth of field scale to determine what aperture setting would produce enough depth of field using that hyperfocal distance (f/16 in this case), set the aperture to f/16 and leave the hyperfocal distance scale set at that distance. That's all you'd need to do in order to focus and ensure the greatest range of sharpness in the photo!

Practical Examples

Diagrams are fun and an easy way to visualize theses concepts, but as we've already mentioned, photographers prefer photos. So we're once again going to use a few of Alberto Bouzón's photos to walk you through the process of using the hyperfocal distance scale, using the Irix 15mm f/2.4 lens.

"Start with a test for the right aperture. If, for example, you place the hyperfocal mark of f/8 (which is the one that I use the most) in line with the focus point, you will see how the depth of field marks that we talked about at the beginning of this article are located as follows:

• The one on the right over infinity marking the far limit. 
• The one on the left is about 2.5 m 

Therefore, at f/8 and with the Irix 15mm focused at the hyperfocal distance for f/8, the focused area will be from two and a half meters [8.5 ft] to infinity. Ideal for [almost] any landscape. And if something we want in focus is outside the near limit, either we change the diaphragm to f/11 or f/16 and the hyperfocal scale to the corresponding number, or we [do some gardening.] (hahaha)

For example, at f/16 the focus bandwidth extends from almost 0.75 or 0.80 meters [2.5 ft] to infinity, adding almost a meter and a half [4.9 ft] more margin to the close limit."

"What About apertures wider than f/8?"

When conditions call for opening the aperture wider, the hyperfocal distance scale doesn't have those numbers. In these situations, the hyperfocal distance is often too far from the camera to be practical for landscape photos.

In this situation, we'll want to weight the pros and cons of opening the diaphragm further or changing the focus point. Hyperfocal distance may not always be the best choice, depending on the intent of your photo.

For instance, as mentioned in the Pro Tip earlier in this article, the preferred focus point for night sky photography will almost always be infinity. Irix lenses incorporate a very convenient "click stop" at infinity to make that a snap!

For further information on photographing the Milky Way, We recommend our 3-part series that starts with this tutorial: An Updated, Comprehensive Guide to Photographing the Milky Way.

If you love landscape photography, it's essential to understand depth of field and hyperfocal distance. As we've shown in the content above, being an Irix shooter means the definition of hyperfocal distance can be simplified as: "The setting I choose on my hyperfocal scale to ensure maximum depth of field in a landscape image."

Other Uses for the Irix Lens Depth of Field and Hyperfocal Distance Scales

Naturally, Hyperfocal Distance focusing has more uses than just landscape photography. This method works well for any genre that calls for maximum DOF. Architecture and large interior spaces, for instance, are good candidates for focusing this way.

The depth of field scale on Irix lenses has a multitude of uses, of course. One in particular that you may have overlooked is focus stacking. Check out this article for a step-by-step tutorial: Focus Bracketing and Stacking Landscape Photos with Irix Lenses (This method can also help improve your macro images.)

Conclusion

As an innovator in the world of photographic equipment, Irix constantly considers the needs of photographers in the design and engineering of our products. Given the need for attention to depth of field and hyperfocal distance, we incorporated markings and scales for both in our lenses. These two features work together seamlessly to help you easily achieve the maximum depth of field in your photos when it's called for.

Together with our focus lock, infinity "click" and other design innovations, Irix lenses put more creative power in your hands!

See you next time!