Depth of Field (DOF) - A discussion by Example

[r_fredrick_smith]

Since another thread spun out of control on this subject, I thought I would introduce it here in the proper forum for further discussion. It is the subject of DOF and how to use it, control it, and so forth. Here is an example of extreme DOF (in this case a macro shot):



This shot is with a Canon 100mm F2.8 Macro lens, shot at F2.8. What you are seeing is about a 1" x 1.5" section of a circuit board. I am shooting down on the board. The highest component is about 3/8" inch high. You will notice that you get areas that are very out of focus. On the other hand, here is the same shot at f35:



I think you will see the incredible difference that DOF can make.

There are a number of good online links to calculators and discussions. One that I like and many others have pointed to is:

http://www.dofmaster.com/dofjs.html

Another interesting article is at:

http://www.bobatkins.com/photography...l/dofcalc.html

So how do you make good use of DOF? When might you want to have parts of your images out of focus? What is the best way to judge DOF? And other questions. These are all things we can discuss and show examples of. Another topic is how to "simulate" DOF in Photoshop. There are good, bad and indifferent ways. CS3 has some better techniques possible because of some new filters.

Cheers,
rfs

[PhotosbyChuck]

Above is a great demonstration of optical DOF using a wide open aperture. Sometimes, you may not have the option and so post processing to create the effect is required.

Here is a simple example of a selective blur to simulate a shallower DOF in PS:

Before: While focus is falling off at the background, the wrinkles are noticeable. I also didn't like the look of the rose over her shoulder as sharp as it appears. I felt the lines competed with the model's outline.

After: The background blur has preserved basic shape of the rose and smoothed out the wrinkles. (I made a contrast adjustment at the same time).



In this kind of shot, since the background is at a constant depth from the camera, the blur applied to it should also be constant. That is, don't blur parts of it more than others. Also, careful selection to extract the model from the background is critical to avoid blurring the model in places while getting all of the background. I'm not an extract pro by any means -- so you can probably find a few places I could have done better!

[RSStory]

Originally Posted by PhotosbyChuck

In this kind of shot, since the background is at a constant depth from the camera, the blur applied to it should also be constant. That is, don't blur parts of it more than others. Also, careful selection to extract the model from the background is critical to avoid blurring the model in places while getting all of the background. I'm not an extract pro by any means -- so you can probably find a few places I could have done better!

I think you did a very good job. Notice how much more the model pops off the screen? That is the best part of a properly used DOF. Doesnt matter if it is in camera or in post. The effect is still the same. It takes an ok shot and makes it a very good shot.

[r_fredrick_smith]

Nice work. I usually use a fairly straightforward method when I want to do selective blurring or DOF. I create an Alpha channel mask which starts all black. I then use a white brush to paint the area I want to keep in sharp focus. I then choose the lens blur filter and choose the Alpha channel as the Source. I then click on Invert and then choose the exact type of blur I want and even a bit of bokeh. I find the Alpha channel method one of the fastest ways to make quick selections. I also use the same idea for using Save for Web and then the Alpha channel mask becomes the area that gets the minimum JPG compression and the rest of the photo gets the maximum compression. I have an article on that subject on G1.
Cheers,
rfs

[RSStory]

Originally Posted by r_fredrick_smith

Nice work. I usually use a fairly straightforward method when I want to do selective blurring or DOF. I create an Alpha channel mask which starts all black. I then use a white brush to paint the area I want to keep in sharp focus. I then choose the lens blur filter and choose the Alpha channel as the Source. I then click on Invert and then choose the exact type of blur I want and even a bit of bokeh. I find the Alpha channel method one of the fastest ways to make quick selections. I also use the same idea for using Save for Web and then the Alpha channel mask becomes the area that gets the minimum JPG compression and the rest of the photo gets the maximum compression. I have an article on that subject on G1.
Cheers,
rfs

I for one would like to see that posted here as well.... If you are so inclined.

Scott

[r_fredrick_smith]

Originally Posted by RSStory

I for one would like to see that posted here as well.... If you are so inclined.

Scott

I can just provide the link to the article:

http://www.glamour1.com/forums/artic...ion-magic.html

Keep in mind that this article shows a different way of creating and using a Alpha Channel Mask that is used for JPG compression. I don't have a article yet on using it for DOF purposes, but if I get the time, I can probably put one together for ShotCritic. But I wonder where articles would go here?

Cheers,
rfs

[RSStory]

Originally Posted by r_fredrick_smith

I can just provide the link to the article:

http://www.glamour1.com/forums/artic...ion-magic.html

Keep in mind that this article shows a different way of creating and using a Alpha Channel Mask that is used for JPG compression. I don't have a article yet on using it for DOF purposes, but if I get the time, I can probably put one together for ShotCritic. But I wonder where articles would go here?

Cheers,
rfs

Great, thanks. I would say put it in this same forum and if there is ever a different location for articles then we can just move it...

[Arbib]

I am not very good at using Alpha Channels, or complicated masking.
So I went a simpler route to ADD DOF in PP...I select the areas with a 2-4pixel feather and added a gaussian blur..
Here is a example I took last year at my wife's company picnic.
I used a XTI with a 28-105 at 105 at 7.1 (I wanted the cards and face in focus)..
So the Background was still too detailed to what I wanted as the final result..
Hence the added PP DOF effect

I think I was successful in the added DOF to create a more isalated subject from the BG. I may have desatuated the BG a bit too..can't remember, but it looks like it..

[RSStory]

Originally Posted by Arbib

I am not very good at using Alpha Channels, or complicated masking.
So I went a simpler route to ADD DOF in PP...I select the areas with a 2-4pixel feather and added a gaussian blur..
Here is a example I took last year at my wife's company picnic.
I used a XTI with a 28-105 at 105 at 7.1 (I wanted the cards and face in focus)..
So the Background was still too detailed to what I wanted as the final result..
Hence the added PP DOF effect

I think I was successful in the added DOF to create a more isalated subject from the BG. I may have desatuated the BG a bit too..can't remember, but it looks like it..

For my taste I would say the gaussian blur is a little too heavily done. And I think a slight contrast adjustment would help a bit as well... Your technique for doing this is pretty close to what I use most of the time.

[Arbib]

Originally Posted by RSStory

For my taste I would say the gaussian blur is a little too heavily done. And I think a slight contrast adjustment would help a bit as well... Your technique for doing this is pretty close to what I use most of the time.

Yes, you are right, it was set quite high...And may look unnatural..I have learned to be more conservative now. Thanks