Depth of Field

[BlueFightingCat]

Hi,

Here's the situation. I have 2 persons sitting on a sofa. I am taking the photo at 90 degrees to get a profile of both persons. One person is leaning back against the sofa and one is leaning forward. What I want to achieve is that have one of the persons perfectly focused and the other one blurred.
I have my camera set to Apreture priority mode and I have it set to the smallest: 3.5. (I use a Tamron 18-270mm lens) and I use the 18mm (~29mm effective).

But I simply can't get the one of the subjects to blur. Can somebody explain how I can get the person in front to be in focus and the person behind to be blurred. And how do I get the person in front to be blurred and the one at the back to be focused?

BFC

[SandeeWig]

Hi BFC

Sounds like you are shooting at the wide end of your lens and even with the open aperture, your depth of field is way to deep.

Check this site out

Put in your camera, 18mm, f3.5 and approximately how far away from your subjects you are shooting.

I entered - just to test - Canon XSi, 18mm, f3.6 and and distance of 5 feet and it told me my total DoF was almost 3.5 feet!

So...in order to decrease your DoF with that lens, you would need to back up and zoom in to a longer focal length. Play with the focal length to figure out how much you would need to zoom in order to get the short DoF you want.

[ttosifa]

Get close or have the subjects move apart.

[kirbinster]

You either need a faster lens, or need to move further away and use a longer focal length to accomplish the effect you want.

[ttosifa]

Originally Posted by ttosifa

Get close or have the subjects move apart.

I could have been clearer -- for a fixed focal length, move in closer or have the subjects move apart. My bad!

[b3nj1]

As others noted, focal length is a good option if you have the room to play with. Larger focal lengths will shrink the depth of field.

Another trick of depth of field is to focus closer to shrink and shift the depth of field. Depth of field is roughly 1/3 in front of the focal distance and 2/3 behind the focal distance. So, you can manually focus in front of your first subject to try to keep them in the range and push the farther person out of the depth of field. This has the added benefit that focusing closer also shrinks the depth of field. Since you're shooting wide-open and the camera is also wide-open when focusing, what you see in terms of focus through the viewfinder is what you'll get. So, you should be able pull the focus forward until you either hit the stop or get the first person just within the depth of focus.

Let us know how it goes.

- Benjamin