Depth of field with the GH3... What am I missing?

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kieranvyas

I am using the Panny GH3 for video and trying to creating a shallow depth of field. I am not obsessed with creating a ridiculously blurred background, but I'm more concerned with creating some blur at a certain proximity from my subject.

In this video, at 03:08 the subjects entire upper body is in frame and a significantly shallow depth of field is still achieved.
http://youtu.be/MT-2VF3-fWo

In this picture, again a large amount of the subjects upper body is in frame with great shallow results. This is using the leica 45mm lens at f2.8
http://www.bestmirrorlesscamerarevi...2013/11/Leica-45mm-macro-sample-images-24.jpg

Now, I have the Panasonic 25mm 1.4 lens, and cannot achieve anything near these results at such a proximity from the subject. Even with the larger aperture.

What am I missing? Thank you!
 
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do you have any sample images we can view? it could be that your prime lens is too wide to create super shallow DOF. i am relatively sure that the longer the focal length, the shallower the DOF. 25mm is pretty wide so perhaps something around an 85mm would give better results.
 
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That makes perfect sense! However, I posted this question on a different forum and received a rather technical answer, now I'm confused again! Their answer was:

The same f-ratio will give you the same DOF for the same framing on the same format. For example, if you took a photo of someone 9 ft away at 45mm f/2.8 and from 5 ft away at 25mm f/2.8, the DOF will be the same.

However, the background blur for the portions of the scene "near" infinity will be proportional to the aperture diameter. Using the example above, the background blur for portions of the scene "near" infinity will be 1.8x more at 45mm f/2.8 than at 25mm f/2.8, since the aperture diameter at 45mm f/2.8 (45mm / 2.8 = 16mm) is 1.8x the aperture diameter at 25mm f/2.8 (25mm / 2.8 = 9mm).

But, the aperture diameter at 25mm f/1.4 (25mm / 1.4 = 18mm) is larger than the aperture diameter at 45mm f2.8, so it will both a more shallow DOF and a greater background blur for the same framing.

So, I'm at a loss as to why you are unable to get the shallow DOF and/or background blur you want with a 25 / 1.4, unless it is because you are framing wider.
Click to expand...

So will a longer focal length create a more blurred background?
 
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When I said
"The wider a lens, the greater DOF"

You can also interpret that to mean

"The longer a lens, the shallower DOF"

There is a ton of technical stuff, math equations, etc. I read about all of that in Cinematography by Blain brown
 
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Sensor size also plays a factor... but here's a little list of how to think about things as you're looking at your scene and it's just not what you're picturing in your head:

You think to yourself...
"Hmm, I would like shallower depth of field"

Your options are:
1. Open the iris more
"But.. I can't, because:"​
  • It's as far open as it can be
    Get a different lens (see option 2)​
  • My image will blow out!
    Add some ND filtration​

2. Use a longer lens
"But..wait a second..."​
  • Now the framing is all wrong
    Move back to maintain the framing you want​
  • It's still not enough and/or I can't move back any farther
    Settle for deeper focus than you were thinking, or try to find an alternate location that will allow you to get further from your subject and your subject further from the background.. and get an even longer lens if necessary.​


You think to yourself...
"Hmm, I would like deeper depth of field.. more in focus as the same time"
1. User a wider lens
"But.. I can't, because:"​
  • I can't get any wider of a lens
    Close the iris (see option 2)​
  • Framing is wrong again
    Move closer to reframe​

2. Close the iris
"Wait a second, now it's too dark!"
Your camera is a glutton for photons and you're feeding it tiny table scrap amounts... Seriously.. Do you understand, at the most basic fundamental level, how a camera produces an image? Turn some lights on! :D
​
 
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kieranvyas said:
So will a longer focal length create a more blurred background?
Click to expand...
What happens is that you are magnifying everything, including magnifying the blur.


Think about it this way: if you're up close to the actors using a wide lens, you are using a wider angle and will see more of the background. If you're farther away, the angle decreases (to keep them actors in the same positions) and you won't see as much of the background... but that means the smaller amount you can see is stretched across the screen. Stretching it out more will cause it to blur more. You do need to be more careful in some ways... the DOF increases as you get farther away. (Obviously, the fullest extent of that is if they are so far that infinity is also in focus.)

The closer you are, the shallower the DOF will be for any lens. Except for maybe pinhole cameras... but then again, pinhole is not a lens.
 
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