Determining aperture for amount of DOF desired

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Determining aperture for amount of DOF desired

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David

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Sorry if I hijacked the PAD thread so here is a thread to discuss DOF.

First, let me recap my question for those that didn't see it. I asked the question if anybody uses any sort of technique or guideline to determine what aperture they need to set a DOF of a certain size for a give focal length.

Let me start of by asking is their a difference between DOF and bokeh? In my mind they are the same. DOF is the area you want clear in the shot while bokeh is the area you want blurred. If I want a 1 foot area around my focus point clear versus the image to start to blur 1 foot after my focus point am I talking about the same thing? In some discussions it seems that DOF and bokeh are referred to as two separate things. Is my understanding correct?

Below is two examples of different DOF. The first shot of the bird is at 220mm f/5.3. It seems to have a very narrow DOF and I wanted to keep the focus on the bird (I know the focus seems to be behind the bird instead on it but hopefully this still illustrates my point). How have you'll come to learn that if you are going to take a 200mm shot at a bird you need to set an f stop of x.

In the second picture is a shot of two swans (i guess they are swans???). This was taken at 85mm f/4.5 but seems to have a much larger DOF. If I was able to take this at 2.8 or 1.4 do you'll just happen to know where the DOF would end if my focus point is the closes swan? If so, how did you'll go about learning this? Just through repetition or by some other means.

** I'm not sure on the rules on posting multiple images so I made them smaller then what we post on PAD. If I need to use smaller images let me know. Thanks

Posted 6 months ago #
golf007sd

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Let me start by saying that there is a big difference between DOF and bokeh. Please read this tread first and see if it helps a bit.

http://nikonrumors.com/forum/topic.php?id=2243

Cheers

Posted 6 months ago #
David

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golf007sd said:
Let me start by saying that there is a big difference between DOF and bokeh. Please read this tread first and see if it helps a bit.

http://nikonrumors.com/forum/topic.php?id=2243

Cheers

Thanks golf, I found the link very informative. So, a lot of variables go into how strong you want the bokeh to be regardless of our DOF. To recap that thread the below is a snip-it from studio460 of all the variables involved to determine how strong a bokeh you want.

studio460 said:
There are five variables which affect the degree of "bokeh:"

1. Aperture: the larger the aperture (numerically, lower, e.g., f/1.4), the less depth-of-field, and the greater the bokeh effect.
2. Field-of-view (angle-of-view): the narrower your angle-of-view (i.e., the more telephoto), the shallower the apparent depth-of-field, and the more pronounced the bokeh effect will be.
3. Size of image sensor: the larger the sensor, the shallower the apparent depth-of-field, and the greater the amount of bokeh.
4. Distance: A. Focal plane-to-subject distance: the shorter the focused distance is to your subject, the greater the amount of bokeh effect on your background.
5. Distance: B. Subject-to-background distance: the further away your background is from your subject, the more pronounced the bokeh is on your background.

You can employ any or all of these techniques to maximize the bokeh effect on your background. For example, say you don't have the budget for that fancy 300mm f/2.8, but what you do have is a 300mm or 400mm f/5.6, maximum-aperture zoom. In this case, you can exploit the telephoto lens' inherent, narrow angle-of-view, use close-focus technique, and choose a really, really far away background to maximize the bokeh effect, even though its maximum aperture isn't that large (see examples, below).

Posted 6 months ago #
donaldejose

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DOF is the area in focus. It depends upon distance from the camera and f-stop.

Bokeh is not just the area out of focus; the area outside the DOF. Bokeh is the quality of the "blur" in the area out of focus. It depends upon the f-stop, the distance from the subject in focus to the background, and the characteristics of the lens. Given identical f-stops and distances involved some lenses will produce better (or at least different bokeh) than others.

The quality of the bokeh which people consider "better bokeh" is a matter of personal preference. Some like to see those big fuzzy circles produced by highlight spots. I don't. I think those highlight circles are distracting. I don't like the white circles msmoto posted as a great bokeh example. I like "creamy, hazy" bokeh in which the colors blend together like you see in a pastel water color painting. Just a matter of preference.

In the two photos above the better bokeh in the top photo exists primarily because of the much greater distance between the subject and those background objects. In the photo of the swans you don't have good bokeh because the out of focus area behind the swans is too close to be greatly out of focus. Think, greater out of focus due to more distance between subject and background = better bokeh as one starting point. And think f1.4, f1.8, f2 or f2.8 = better bokeh as another starting point. Then shoot with those concepts in mind and gain experience.

Posted 6 months ago #
golf007sd

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David which lenses do you own?

Posted 6 months ago #
David

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Here are my lens.

Nikkor 18-105 VR 3.5-5.6
Nikkor 70-300 VR 4.5-5.6
Nikkor 50MM 1.8D

Posted 6 months ago #
donaldejose

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Try shooting the 50mm 1.8D at f1.8 and f2 for bokeh.

Posted 6 months ago #
David

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donaldejose said:
Try shooting the 50mm 1.8D at f1.8 and f2 for bokeh.

Earlier in the month I was doing some testing with fill flash while also testing bokeh. My objective in the below pics was to get the front of the plant to the flag in focus while blurring everything else out as much as possible. To help with scale the curtains in the first two pics are 11 feet behind the plant. In the third pic the railing for the stairs is 15 feet behind the plant. The first shot is 50mm f/1.8 while the second shot is 220mm f/5.3. The 50mm shot has way to small a DOF while the 220mm is close to what I am looking for. Also, I think the 220mm shot has a stronger bokeh then the 50mm f/1.8. This surprises me because at that large an aperture I would expect the 50mm to be better here. Now lets take into account the third picture. It is at 50mm f/4. Seems to have about the same DOF as the 220mm (50mm I think a tad bigger) but the bokeh seems weak compared to the 220mm and given that the railing is further way then the curtains.

**Moderators, I apologies if I am posting to many pics but don't know how else to illustrate my point. To make up for this I will avoid posting to PAD for a little while.

Posted 6 months ago #
roombarobot

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David, you can also get a sense for the depth of field by playing around with some of the online calculators, like this one:
http://www.dofmaster.com/dofjs.html
Just put in your variables and it will tell you the depth of field.

Posted 6 months ago #
TaoTeJared

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DOF is very different from Bokeh, but they are related to each other. Another topic you may want to do some research on is "Circle of Confusion."

Sharp area (in focus):
Focus distance when locked on a subject-sharp range = 1/3 of DOF in front of the focus point, & 2/3 behind the focus point is sharp. That is the DOF or Sharp range. From there, the sharpness falls off.

Posted 6 months ago #
msmoto

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Something not really mentioned is the relationship of apparent DOF to the viewing distance and size of the final image. As we enlarge an image, what may appear sharp in one size, falls apart as it gets larger at the limits of the initial apparent area of sharpness.

On NRF in the PAD, viewed at 1000 px on Flickr and image may be sharp due to the finite amount of sharpness available on a monitor. But, as one views the image at sizes which approach the full size image, one might notice the areas of the image which were sharp in the smaller versions are now slightly fuzzy. And these are near the limits of the DOF calculations.

All of the above assumes an image which is "sharp" in the sense of lens resolution and dos not show any motion blurring.

Here is an example at the 800 px size

And, when one looks at the 3000 px size it becomes apparent the DOF is "apparently" less http://www.flickr.com/photos/fantinesfotos/8114147211/sizes/o/in/photostream/

In fact while the DOF initially is possibly 8 inches (20 cm) it is seen in the larger view to be maybe 2 inches or 5 cm.

D4, 24mm f/1.4 Nikkor 1/160 sec, f/11 - 0.7 ev, ISO 220

Please note, the actual DOF is not changing, only the ability to see the image more clearly enlarged and understand that in this image, fairly close focusing, the DOF is very small even with a 24mm lens at f/11. And, this is one of the many factors which make the discussion of DOF difficult as there are multiple variables in the final analysis.

Posted 6 months ago #
spraynpray

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Depth of Field is points of light becoming discs or circles of confusion and gets shallower by:

Getting closer with the same lens,

Using a longer lens at the same distance,

Using a larger aperture,

Blowing up the image larger,

Viewing from closer.

Obviously the DoF gets deeper in the opposite circumstances.

Contrary to what some think, if you keep the image size the same when changing lens length by zooming with your feet, the DoF stays very nearly exactly the same.

http://www.parkwoodcameraclub.co.uk/articles/dof.htm

Posted 6 months ago #
donaldejose

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David: You are doing what you need to do. Practice changing variables to learn how to achieve what you are seeking. Apparently, what you want is to have the subject in sharp focus while the background blurs away. In order to keep the entire subject in focus at f1.4 you need a flat subject. Look at the fern photo I posted a few days ago on PAD. I deliberately selected a flat fern because I knew I was limiting myself to f1.4. You are also learning that to blur the background at 220mm that background will have to be about 15 feet away from your subject. These are just the physical/optical constraints required to produce the effect you seek. Notice that these constraints are not met in the photo you posted of the penguin. You simply cannot blur the birds body as you wanted to do because that body is not 15 feet behind the head. If you had a 400 f2.8 lens you might be able to keep the head all in focus and blur the body more.

Posted 6 months ago #
golf007sd

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Here is an example of what donaldejose is trying to explain to you David. My focus is on the paw, see how the cat's body is completely blown-out. Keep in mind this shot was taken from like 2 feet away!

D4 24 1.4G 1/200 ISO 800 @ f/1.4

Posted 6 months ago #
David

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What I have been working on is controlling the amount of bokeh while maintaining a certain DOF. After playing with the DOF calculator I ran some test on the different ways you control bokeh. In my test I used the plant from above and place the flag 1/3 way back from the front flower. I set the focus point on the flag and used the DOF calculator to maintain 4" of DOF. The reason I want a fix DOF is because this how I think about the shot. I look at what I want to shot and try to figure out how much of it I want in focus and how fast I want to drop out of focus after that point. I don't know if everybody thinks about shots like that.

For the close up test I used 18mm f/6.3 from 15" to get my 4" of DOF.

For aperture test I used 50mm f/1.8 from 75".

For telephoto I used 230mm f/5.6 from 17 feet.

While the DOF calculator says the DOF is the same between the shots the pics say a different story. 230mm gave a bigger DOF while giving a stronger bokeh. 50mm shot came a close second with a little less DOF and a little less bokeh. 18mm was the worse with a lot shallower DOF with a weak bokeh. What this seems to tell me is that telephoto is king if you want a strong bokeh. It gave me a bigger DOF and strong bokeh if you can get far enough way from your target. Aperture came in second if you have enough megapixels to compensate for the large crop needed for the size of the object I was shooting. Close up shot maybe just isn't close enough to matter or that 4" DOF is just to big for a close up shot. So, is this correct if you want a strong bokeh while maintaining a certain DOF nothing beats telephoto???

Posted 6 months ago #
SquamishPhoto

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Depending upon your subject and how much of your scene is being rendered in focus you can shoot two frames, each at the optimal aperture for focus and also for bokeh, and then blend them in post.

Posted 6 months ago #