Camera Parameters: F/Stop and Depth of Field

Author:

robert952

Tools Needed

* DAZ Studio

Support Files

* FStopSupport.zip

While there are some basic tutorials around for the F/Stop and Depth of Field, I felt that a different approach would be useful. Instruction manuals and books on photography usually illustrate how different settings affect your image. I took that same approach for this tutorial. To assist your learning, there is a support file so that you can experiment and follow along with this tutorial and apply the exact steps outlined. I will use this file throughout this tutorial. The file is nothing spectacular, just a variation on the famous (or infamous) 'faerie tutorial' of the manual. Of course, the role of the faerie will be played by the ever so versatile Vicky and our well trained dragonfly joins the scene. Vicky is dressed and posed for the scene and lit with a spotlight on her face and a distant light overhead. Everything is locked except for the Camera controls of 'Main View' so that you don't inadvertently move something. Feel free to unlock anything you want to play with during your learning experience. You can always reopen (or download another copy) of the file. You may find it useful to follow the examples for of this file. Or you can easily create your own and follow along using the appropriate parameters from your composition.

As I learn about DAZ Studio, I find it helpful to tie what happens in the software to real world items. For those who find such background useful here are some definitions and theory around the Depth of Field and F/Stop controls.

F/Stop: In the real world, F-Stop (or F/Stop) is a ratio (which is why it is written with a slash) of the length of a lens over the size of the aperture letting the light through. A lens of 50mm length with an aperture opening of 25 mm has an F/2 setting. If the aperture is smaller, say 10mm, then the F/Stop is 50/10 or F/5.

Focal Distance: The distance from an object or point you are focusing on through the lens to the film plane of a camera (or focal point). In Studio, you cannot actually focus on an object like you can with a real world camera. The next section covers this critical parameter in using Depth of Field to your advantage.

Depth of Field: All lenses have a depth of field where the subject and items in front of and behind the subject are all in what is called the 'range of acceptable focuses. This range of focus (where everything is in focus) falls 1/3 of the distance in front of the subject to 2/3 the distance behind the subject for any given F/Stop. This area is the Depth of Field. Anything outside of that Depth of Field becomes out of focus and appears fuzzy in photographs (and, we'll see, in your 3D renders).

Putting this all together allows a photographer (and DAZ Studio artists) to control how much of a scene is in focus. Increasing the F/Stop increases the depth of field within the focal distance. The higher you set the F/Stop the more of the scene that is in focus. The figure below should help put this together for you in general terms.

The important issue is that as you increase the F/Stop to a higher number, the greater the depth of field and the more elements are in focus in your scene.

When you render in DAZ Studio with no Depth of Field everything is in focus as you can see from the render below. From her fingertips to the wing in the background, every point is in focus. So, distance is not critical.

But, to use the Depth of Field options, you need a decent idea of where your focal point falls in the scene in relation to the camera. You have to have a Focal Distance that is a specific distance from your camera.

Using a 'Null Point' and a bit of math, you can determine the Focal Distance to a point in front of your camera. The standard 'Windows' calculator is all you need since it has a square root key (sqrt).

Any two points in a 3D space have coordinates:

Point A = (Ax; Ay; Az)

Point B = (Bx; By; Bz)

Calculate the difference between each respective coordinate (dX = difference of X coordinates and so forth).

dX = Ax – Bx

dY = Ay – By

dZ = Az – Bz

Then, Distance = the square root of (dX * dX) + (dY*dY) + (dZ * dZ)

(To be clear of the math required, I thought it better to show the math instead of simply saying 'dX squared' above. The '*' means multiply.)

I created a Null Point (using File Menu: Create/New Null Point) and placed it at Vicky's nose:

X = 7; Y = 169; Z = 28

All renders are from the camera called 'Main View' at coordinates:

X = 75; Y = 133; Z = 85.

Applying the math:

dX = 7 – 75 = (- 68)

dY = 169 – 133 = 36

dZ = 85 – 28 = 57

(Note: the negative sign for dX goes away in the next step, so don't fret over it.)

dX squared = 4624

dY squared = 1296

dZ squared = 3249

The sum of the above 'squares' = 9169.

And the square root of 9169 = 95 (rounding off the fraction part to get a whole number that's close enough for our need.)

Now, let's apply that number.

Now before we get too far along, let's decide what we want to accomplish in our image. Our original scene is Vicky (in the role of the faerie) and a dragonfly. We want to create an image where there is a visual relationship between Vicky and friendly insect. We are going to use the Depth of Field to do that. (And, of course, we want to learn how to use the tools we have in Studio.)

Select the Main View camera in the Scene tab. Once that is done, you will find the camera controls at the bottom of the Parameters tab. There are five controls for a camera.

The first control (Perspective) should be left on.

The Focal Length represents the lens. We will use this 'normal' 50 mm lens for our image.

The next control turns on the Depth of Field of our camera and the rendering software. It is a toggle, clicking on it turns it On and Off. Be sure it is 'On'.

Focal distance is the central focusing point of our image. Click the number field and type in 95 (the Distance we calculated earlier).

F/Stop is the last control. The default setting of 22 is a good starting point for our image.

Now, render away. And you will get the following:

The software (as expected) rendered Vicky's face in sharp detail. The out of focus wing in the background adds depth to the image as does the blurred hands in the foreground.

Our dragonfly is a bit out of focus and we want to bring him into focus. But before we do that, let's look at a couple more renders to see what the F/Stop does with different settings.

Let's open up a couple of stops and use F/Stop of 11.

Well, if we wanted a tight relationship between Vicky and the dragonfly, this render isn't going to do it. But, we do see less focus on her wing (which could be a good thing) and a lot less focus on the dragonfly and her hand. That's want I wanted you to see.

So, one more render at F/Stop of 64 and we get'

An image that is almost the same as that with no Depth of Field. Her hand is a bit out of focus but not by much. The lesson here is that there is a point of diminishing returns on the higher depth of field which for this exercise is around F/Stop 64. (Also, in the real world, there is an infinity mark on a lens that falls over the highest F/Stop for that lens.)

But, let's return to original thoughts for the image.

The intent was to create a visual relationship between Vicky and the dragonfly. The first attempt at F/22 and Distance of 95 was not too far off for a first attempt. So, let's look at that one again.

We want to bring the dragonfly into focus more. There were three ways to achieve our desired goal: change the F/Stop, change the Focal Distance, and a combination of both.

Let's do the first and change the F/Stop to something more than 22 and less than 64. So, let's try F/Stop 45. For those with a photography background, you'll note I use the standard settings' old habits are hard to break. You can use any value for the F/Stop you want in Studio and are not tied to the real world.

But at f/45, we get this result:

Hmm-not bad. But the background wing seems a bit too sharp and the dragonfly needs to be sharpened up some more.

So, for this final render let's move the Focus Distance forward a bit to a point between Vicky and the dragonfly. Let's also adjust the F/Stop. No math, just a guess as to where might it just 'seems' right. After all, we're artists and allowed to do that kind of thinking.

I picked distance of 80 (15 cm closer to the camera) and F/Stop of 40.

And this meets my objective quite nicely. We could play with the settings more. But, by now you see what you can do with Depth of Field.

As I said early in the tutorial, you can use depth of field to draw attention to a specific part of your image.

You can use depth of field to add mystery to your image.

In the above image, we see our talented faerie dancing in the forest. Adding a foreground figure and blurring the focus adds depth to the image' and mystery. Who is that watching her? Does Vicky know she has an audience? Is there danger lurking?

Also, as one final example, you can use soft focus to save some post rendering work.

In this image, I created the candle flames using a couple of conical primitives with a point lights inside the primitives. Of course, they look unrealistic.

I could do some post work on the flames in Paint Shop Pro or Photoshop. But I can also improve the image with Depth of Field control. Using the same steps as shown in this tutorial (create a Null Point near Vicky, calculate the distance from camera to Null Point and applying the factors to the camera controls) I made the flames softer, as well as blurring the foreground and background).

So, you see the power of the camera controls and how they can help you with your DAZ Studio compositions. And you'll find this methodology works whether you want to focus on an object in your scene or a part of the anatomy of your favorite figure.

Have fun with your new found knowledge.