Can't get my head around DOF...

MagicMynx · May 31, 2009

I can do DOF where the background is blurry, that's no problem, or where the whole picture is in focus, again, no problem, but I can't seem to get the foreground blurry and the background in ocus ... well, not intentionally anyway.

Could anyone advise please?

Jaszek · May 31, 2009

just set your autofocus point at the background, if you have it set to automatically chose a focus point for you set it to select a focus point manually, or focus manually. What camera do you have?

MagicMynx · Jun 1, 2009

I'm using a Sony Alpha 350. Also have a fuji finepix s8100fd which isn't a DSLR.

Am I right in thinking that I'm simply relying on the computer too much - waiting for the little green light to tell me that it's correctly in focus?

Big Mike · Jun 1, 2009

The DOF of a photo, extends 2/3 behind your focus point and 1/3 back toward you.

So for example, if you subject is 10 feet away and you aperture is set to give you a 3 foot deep DOF...you DOF will be from 9 feet to 12 feet.

So if you want your subject to be in focus while having the foreground blurry, you just need to ensure that your DOF is shallow enough and most importantly, that you are accurately focusing on your subject.

It's not uncommon that the camera's AF system will pick up something that is closer or brighter than you subject, which is why it's important to take notice of what the camera is focusing on.

The way I do it, is to separate my focusing from the shutter release button, and I only use one focus point at a time (usually the middle point). So I put my active point on my subject and activate the AF. When I'm sure that my subject is in focus, I deactivate the AF and take the shot, recomposing if I have to.
A similar method would be to lock your AF after focusing on your subject. Some cameras do this when you half press the shutter/AF button for a half second or so.

Of course, you could just switch off the AF and focus manually.

SouthEastFirePhoto · Jun 1, 2009

Take a look at this......

Online Depth of Field Calculator

It is a great tool to get a look at some different lenses and how the focal distance and aperture will affect DOF.

bigtwinky · Jun 1, 2009

1- Try getting off the auto focus points and set a single focus point to the middle/centre dot on in your viewfinder. Not sure how to do this on your Sony

From there, put that point on something in the background and half press the shutter button. Your camera should then focus on this one point.

Still holding the butter half way, recompose your shot... ie move the camera, keeping the button pressed, to what you want to shoot.

Then shoot.

2- There is a switch on your lens to go from Autofocus to Manual Focus. Switch it to manual. This disables the autofocusing in your lens and allows you to use your focus ring on your lens to set the focus yourself.

While looking through the view finder, turn the ring and look at the effect on the what is in focus. One extremety has whatever is closest to the camera in focus, the other has the background in focus.

Hobbes · Jun 1, 2009

Does your camera have DOF preview button?
If it does then it's pretty easy to see it through the viewfinder.

MagicMynx · Jun 2, 2009

Thanks everyone.

Just for the record - I hate auto focus for stuff like that, on my DSLR I rarely use the auto anything and it's usually set on manual. I know that I can do stuff on auto...but I prefer not to.

MagicMynx · Jun 2, 2009

Hobbes said:
Does your camera have DOF preview button?
If it does then it's pretty easy to see it through the viewfinder.

I don't think so

jbhaferkamp · Jun 2, 2009

SouthEastFirePhoto said:
Take a look at this......

Online Depth of Field Calculator

It is a great tool to get a look at some different lenses and how the focal distance and aperture will affect DOF.

@SouthEastFirePhoto

That's a great tool. Thanks for sharing it.

jbhaferkamp · Jun 2, 2009

MagicMynx said:
I can do DOF where the background is blurry, that's no problem, or where the whole picture is in focus, again, no problem, but I can't seem to get the foreground blurry and the background in ocus ... well, not intentionally anyway.

Could anyone advise please?

If it's a person that is the subject you want to be blurred, then have them set up where they will be in the shot and then ask them to take a step to one side or the other to get them out of the frame. Then set the focus on the background and have the person step back into the frame. Release the shutter and voila!

If it's a manual focus camera it should be easy. If it's auto focus, there should be a way to press the shutter half way and then recompose. On my Nikon, there is a focus/exposure lock button that has to be held down simultaneously to perform this type of shot. Check out your camera's manual, it should tell you how to do it.

farmerj · Jun 2, 2009

jbhaferkamp said:
On my Nikon, there is a focus/exposure lock button that has to be held down simultaneously to perform this type of shot. Check out your camera's manual, it should tell you how to do it.

You can also place it on AF-S, focus on a distant item, recompose and then take the picture.

You can use the AE-L button to set and hold the exposure, the AF-S to set the focus on a specific point.

Just like computers, several different ways to do the same task.