This came up tonight, so thought it may help someone else as well.
What determines what your depth of field is? Most think that the aperture size is the most important factor for the size of the field. This isn’t true at all.
The three factors that determine your depth of field are:
- Your final focal length, by which I mean your lens’s focal length x your sensor magnifier.
If you have a crop sensor, for example a 40D, your magnifier is a 1.6. So a 50mm lens is actually a 80mm lens.
The factor is that the longer the focal length the smaller your depth of field is.
Example: With everything else equal, a 50mm lens has a depth of field of 5 feet, but a 200mm lens at exactly the same situation will have 3.6 inches of depth.
- The distance from you to the subject.
How close the subject is to you is also a very important factor, or rather your focus point is the determining factor.
The closer your focus point (past your minimum focusing distance) is to your lens the smaller the depth of field is going to be.
Example: A 50mm lens focusing at a subject 8.6 feet away (100 inches) will have a depth of ~45 inches. If the same subject was moved closer to the lens, say 16 inches away the depth of field would be reduced from 45 inches to 1 inch.
- Lastly, the aperture size of your lens.
The last option is the size of your aperture, as the smaller the aperture is the more depth of field you will have. Same goes true for the opposite, the larger your aperture size is, the less depth of field you will have.
Example: At f/7.1, the depth of field could be 1.3 feet. However at f/2.8 the depth is going to be reduced to 0.5 feet, and f/32 5.8 feet of depth.
This is also in order of most effectiveness, the longer your focal length the less the aperture size matters. Same is also true for the distance to subject and your aperture. The focal length and the distance to subject are just about neck and neck as far as importance. Both have a huge effect on the final result, however again the change in size of the focal length does more to effect the size of the field than the distance to the subject.
Smart Objects was introduced back in CS2. At the time, I did not find much use for it, but recognized that it can come in handy in some occasions. They do make certain types of changes harder, some functions are not available when using Smart Objects, but they are an excellent tool for non-destructive changes. Here is a case where they came in extremely handy:
I have started doing a lot more with Photobooks lately. The first “real” wedding book that I did, took about 12 hours total from scratch (no templates). If I had not started with objects that time would have been doubled or even tripled. The time savings comes from being able to move images around, resize, and reposition them easily and without having to go back to the source.
What is a smart object?
A smart object is a “copy” of an image, be it a photograph, vector art, or just about anything that can be its own file and layer. The object is inserted, as is, into a layer which can be acted upon without modifying the source.
Why use Smart Objects?
The easiest way to tell you is to show you.
- Find a small image that you would like to test with. Create a file in Photoshop that is the same, or slightly larger. Use “White” as your background. Please note the size of the “test” image. We’ll assume 400 px X 400px.
- Open your image, and Copy its content. Select All (CTRL+A), Copy (CTRL+C).
- Switch to your newly created empty file, and Paste (CTRL+V)
- Notice the smoothness of the image.
- Edit -> Free Transform or CTRL + T
- In the toolbar for the Transform change, change W: 100px, and H: 100px (25% of the original), and Click the Check Mark.
- Now increase the size of the layer back by reversing the process.
- Edit-> Free Transform or CTRL+T
- In the toolbar for the transform tool, change W: 400px and H: 400px back to the original size of the image.
- Notice how badly the image is pixilated. This is because the act of reducing the image is destructive. All extra data after the change is lost. So if you try to increase the size or get a color or part of the image back – it’s gone.
Now repeat the process, except:
Instead of 1a, 1b, 1c … use File -> Place, and insert the “test” insert as a smart Object. Also instead of using “px” as the size you can use 10% as the scale option. When you go back to try to increase the size of the layer again, it knows that it is at 10% and you can use 100% to go back to the original size.
