Help with Depth of Field

[Humbre]

I have soften or blurred out the backgrounds of flowers, faces, etc. But I have never done it on a large subject like a car or motorcycle. I just can not do it or is it possible? I have been up and down the focal length with the zoom with the aperture at 2.8 but I can not soften the background of a car. With the 12x zoom all the way out I am about a good 50 to 60 feet. I can not get any closer and keep the car in the pic. The back ground is about 300 feet away. Is there something I am missing or do not understand. Can you help?

Thanks

 

[jaymc]

If you're using a compact p&s, then you won't have much luck getting the results you want. This is one reason people buy DSLRs.

• Jay

 

[Patrick Wu]

One thing you didn't describe is your lens' focal length.

You don't need to get any closer. You just need longer focal length, the longer the better. Bob Atkins has a DOF calculator. See http://bobatkins.com/photography/technical/dofcalc.html

An alternative is to park it at a location that has a background that you can easily remove with Photoshop.
--
http://wupatrick.com

but I can not soften the background of a car. With the 12x zoom all
the way out I am about a good 50 to 60 feet. I can not get any
closer and keep the car in the pic. The back ground is about 300
feet away. Is there something I am missing or do not understand.
Can you help?

 

[Humbre]

Hey! Thanks for writing. The only answer I can think of that would be logical is, when a camera is in the infinity range and further. The depth of field rules can not be applied because the camera put every thing in focus in infinity. Do you feel there is any merit to my thinking. I can not get any closer and still keep the car in the pic.

 

[Alan Martin256506]

I have soften or blurred out the backgrounds of flowers, faces,
etc. But I have never done it on a large subject like a car or
motorcycle. I just can not do it or is it possible?

With the background so far behind the subject, the amount of blur depends mostly on the size of your lens' entrance pupil relative to the size of the subject. So to get the same effect with a larger subject, you need a lens with a larger pupil.

It sounds like you're using an FZ20, which has a 26 mm pupil at maximum zoom and maximum aperture - that's as good as it gets with small-sensor digicams. Some SLR lenses feature pupils as large as 150 mm, but they're not cheap!

You could try focusing on something closer than the car, trading off a little softness for more background blur. But it won't help very much.

You could also blur the background in postprocessing, but it's very difficult to do a good job. It's relatively easy to draw an accurate outline for a car, but it won't look natural if the ground under the wheels is blurred as heavily as the distant background.

--
Alan Martin

 

[SMC2002]

of P&S cameras. The advantage is you get a nice deep DOF, all the time. The disadvantage is that it's very difficult to get a shallow DOF. Your lens needs to be wide open and your subject needs to fill most of the viewfinder to even have a chance.

As mentioned, if you want shallow DOF's, get a Dslr.

Steve

--
Everyone has a photgraphic memory......some just don't have any film

http://www.pbase.com/slo2k
http://freezeframephotography.smugmug.com
http://www.photobird.com/steve

 

[tko]

DOF decrease as the subject magnification becomes larger. We've all seen this effect - take a picture of an ant and you have hardly any DOF, take a picture of a building and you have all the DOF in the world.

DOF also changes with sensor size. Double the sensor size, cut the DOF in half.

Lastly, DOF changes with aperture, as we all know.

There is nothing else you can do to change DOF. Subject to the above, nothing else changes DOF - not the lens, the perpective, or the zoom.

So, you really want a smaller DOF w/your car you need either 1.) a larger sensor size or 2.) a larger aperture. If your already using full frame and say, F1.4 there is nothing more you can do.

In the case of your car it's probably easier to simulate DOF using Photoshop or equivalent.

 

[Klipsen]

DOF decrease as the subject magnification becomes larger. We've all
seen this effect - take a picture of an ant and you have hardly any
DOF, take a picture of a building and you have all the DOF in the
world.

Exactly. Magnification is a combination of subject distance and focal length. That, and only that, determines DOF.

DOF also changes with sensor size. Double the sensor size, cut the
DOF in half.

Wrong. Only correct if you make the subject fill the same proportion of the sensor. For the same magnification, DOF is the same.

Lastly, DOF changes with aperture, as we all know.

True.

There is nothing else you can do to change DOF. Subject to the
above, nothing else changes DOF - not the lens, the perpective, or
the zoom.

So, you really want a smaller DOF w/your car you need either 1.) a
larger sensor size or 2.) a larger aperture. If your already using
full frame and say, F1.4 there is nothing more you can do.

Except make enough distance between the subject and the background.

In the case of your car it's probably easier to simulate DOF using
Photoshop or equivalent.

True.

 

[jaymc]

... especially the "CLARIFICATION: FOCAL LENGTH AND DEPTH OF FIELD" paragraph?

• Jay

 

[jaymc]

oops, here's the page:

http://www.cambridgeincolour.com/tutorials/depth-of-field.htm

 

[Alan Martin256506]

DOF also changes with sensor size. Double the sensor size, cut the
DOF in half.

Wrong. Only correct if you make the subject fill the same
proportion of the sensor. For the same magnification, DOF is the
same.

As has been explained in many previous threads, for the same magnification a larger sensor actually has more DOF. Remember, the DOF formula is not format-independent, it requires a "circle of confusion" value that should be proportional to the format size. That's because the notion of DOF is based on perceptions of sharpness in a print.

However, keeping the same magnification rather than the same framing is clearly irrelevant to the OP's question.

--
Alan Martin

 

[tko]

DOF also changes with sensor size. Double the sensor size, cut the
DOF in half.

Wrong. Only correct if you make the subject fill the same
proportion of the sensor. For the same magnification, DOF is the
same.

Well, yes, depends on your definition of magnification. For object to image size, you are correct, sensor size doesn't matter. But for object to same percentage fill of sensor, it does matter. An important distiction.

Most people would say, fill the sensor with a persons face, regardless of sensor size, so from the practical viewpoint it does change w/sensor size.

 

[Patrick Wu]

Lest it becomes too complicated, all things being equal here are three things you can do to decrease the depth of field:
(1) Use a larger aperture (i.e., open it wide, e.g., f1.8);
(2) Use a longer-focal-length lens (e.g., 800mm);
(3) Move closer to the subject.

For more info, see International Center of Photography’s Encyclopedia of Photography on Depth of Field.

--
http://wupatrick.com

 

[Alan Martin256506]

DOF decrease as the subject magnification becomes larger. We've all
seen this effect - take a picture of an ant and you have hardly any
DOF, take a picture of a building and you have all the DOF in the
world.

DOF also changes with sensor size. Double the sensor size, cut the
DOF in half.

Lastly, DOF changes with aperture, as we all know.

There is nothing else you can do to change DOF. Subject to the
above, nothing else changes DOF - not the lens, the perpective, or
the zoom.

This analysis is only an approximation, valid when the DOF is shallow as compared with the camera-to-subject distance. When DOF is large, or when considering background blur rather than DOF per se, perspective does make a difference.

Paul van Walree has a long web page about DOF, and another with the details of the calculations. Here's what he has to say about background blur:
http://www.vanwalree.com/optics/dof.html#backgroundblur

I believe that the OP wants to maximize what this page calls "absolute blur", i.e., would prefer photo A to photo B even though particular objects in the background can be seen with the same level of detail.

It is of course possible to work this out in terms of focal length, aperture, magnification, etc., but for a background much more distant than the subject, it all boils down to pupil size vs. subject size as I explained. The size of the pupil (which can be seen by looking into the front of the lens) is the focal length divided by the f-number.

--
Alan Martin

 

[Klipsen]

However, keeping the same magnification rather than the same
framing is clearly irrelevant to the OP's question.

Firstly, I commented on another post.

Secondly, it is very relevant, inasmuch as it explains why he cannot get more DOF by changing lens, only magnification. If he want's the car to fill 80 % of the frame, then with any lens DOF will be the same at a given aperture.

I really can't see the relevance of bringing sensor sizes into this debate, simply because I can't imagine anyone changing camera body to obtain an increase or decrease in DOF.

 

[Klipsen]

DOF also changes with sensor size. Double the sensor size, cut the
DOF in half.

Wrong. Only correct if you make the subject fill the same
proportion of the sensor. For the same magnification, DOF is the
same.

Well, yes, depends on your definition of magnification. For object
to image size, you are correct, sensor size doesn't matter. But for
object to same percentage fill of sensor, it does matter. An
important distiction.

And that's why I make it. You started out talking about magnification, but then switched to fill-grade; and the two should not be confused, although they often are.

 

[Klipsen]

If you're asking me: It is exactly the same things that I said.

 

[Alan Martin256506]

However, keeping the same magnification rather than the same
framing is clearly irrelevant to the OP's question.

Firstly, I commented on another post.

Yes, and you objected to the statement that DOF is smaller on a larger sensor, which is true when you keep the same framing as the OP clearly intended.

Secondly, it is very relevant, inasmuch as it explains why he
cannot get more DOF by changing lens, only magnification. If he
want's the car to fill 80 % of the frame, then with any lens DOF
will be the same at a given aperture.

This is a good approximation when DOF is shallow as compared with camera-to-subject distance, and sensor size is fixed. But it is not true in general, and it certainly doesn't apply to blurring a distant background.

You can see the advantage of a longer lens for background blur in photos A and B here, both taken at f/4:
http://www.vanwalree.com/optics/dof.html#backgroundblur

--
Alan Martin

 

[nickleback]

If your already using
full frame and say, F1.4 there is nothing more you can do.

If by full frame you mean 35mm, there is something you can do... go to a larger format.

--
Seen in a fortune cookie:
Fear is the darkroom where negatives are developed

 

[tko]

Neither lens focal length nor subject distance will change DOF providing magnification stays the same. If you want the car to say, occupy 75% of the image, the DOF only varies with sensor size and aperture.