Problem with depth of field

[beantowner2]

I have a Canon PowerShot G12 and haven’t been able to vary the depth of field in my photos.  When I set it to aperture priority with a low f stop, the depth of field looks the same as if I use a high f stop.  It also looks the same as if I shoot the picture on Auto.  What’s wrong?

[Waddizzle]

Most likely distances between camera, subject, and background.

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

To use this table effectively, look up your camera model in the drop down list.  It's way down the list with other compact cameras.

[jrhoffman75]

If you are shooting at the wide angle rangle of the camera the depth of field will be very great even with a wide open aperture.

[diverhank]

To maximize the depth of field:

1. set largest aperture (lowest Av value)

2. Put your object farther away from the background

3. Move your camera as close to subject as possible

4. Zoom in as much as possible (if your lens is a zoom lens). The higher the Focal Length, the more depth of field you'll get.

For wide angle focal length, depth of field is deep and you might not be able to blur the background enough.

[ScottyP]

Also, the smaller sensors of the Powershots naturally give more DOF than a larger sensor.   You may need to use most if not all the 4 strategies listed above at the same time to get the shallow DOF look you want. 

[beantowner2]

For the photos I'm doing, I usually don't have any control over how close I am to the subject.  What size sensor do I need in order to get reasonable control over dof - preferably equivalent to what I got with my old Olympus film camera?

[Waddizzle]

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@beantowner2 wrote:

For the photos I'm doing, I usually don't have any control over how close I am to the subject.  What size sensor do I need in order to get reasonable control over dof - preferably equivalent to what I got with my old Olympus film camera?

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Without knowing specific distances or focal lengths, there is no way to give you a specific answer. 

If you have not taken a look at the link that I posted above, I strongly encourage you to do so.  You will be able to compare apparent DoF between different cameras, distances, and focal lengths with just a few clicks.  While film cameras are not listed in the database, select any full frame camera body, and it should give you equivalent results.

[beantowner2]

I did check the link you posted.  Thanks for that information. (Sorry to take so long replying.)  I didn't know where to start looking in the data to find what I wanted, so was hoping for a seat-of-the-pants answer.

[jrhoffman75]

You will get the shallowest DOF your camera can provide  by setting the aperture as wide as possible, the zoom setting as long as possible, and using the closest focus for your lens.

"As a practical matter, these are the the things that affect depth of field:

the f/stop
The smaller the f/stop (the larger the number, the smaller the diameter of the aperture), the more depth of field there is. At f/2 (small number, big aperture), you will have comparatively narrow depth of field, with little in focus on either side of your focus point; at f/16 (big number, small aperture), you will have comparatively more depth of field, with more subject matter in focus on either side of your focus point. I say "comparatively" for a reason. If you've read my f/stop page, you know that from a brightness point of view, measuring the amount of light hitting the film or sensor, f/2 is f/2 regardless of the lens. This isn't the case with depth of field. The amount of depth of field at f/2 will also depend on...

...the focal length of the lens
The shorter your focal length, the more depth of field you will have. A 20mm lens will have more depth of field than a 50mm will have more than a 100mm. With really short lenses, like 4 mm, you will have immense depth of field. With long lenses, like 400mm, you will have miniscule depth of field.

the distance to the subject
The closer you are to your subject, the less depth of field there will be. The further away you are, the more depth of field you will have."   From - "http://www.uscoles.com/depthoffield.html"

Whether or not that is an acceptable DOF for your purposes only you can decide.

[jrhoffman75]

Hi diverhank. I think you have some errors.

Minimize DOF, not maximize. 

Higher the focal length less DOF.