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Old Nov 17, 2011, 4:53 PM   #1
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Default exact depth of sharpness

hello, i am new to digicams!

i want to learn how to make pictures with a low depth of sharpness. so only the face from my model (Susi), a few centimeters backwards all is blurish.
see example picture attached.

how can i do this?
do i need a special lens or can i do this with an olympus model Pen-Lite Ebl3 with lens 14-42mm or lens 40-150mm.
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Old Nov 17, 2011, 5:19 PM   #2
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There are a number of things you can do to get a shallow Depth of Field.

The easiest is to use as large an aperture as possible. With the two lenses you mentioned, that won't actually get you very far. Another is to position your subject so that the background is far away. The farther away it is, the more out of focus it will be. Lastly, get as close as possible to your subject. That will increase the relative distance between the subject and the background.
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Old Nov 18, 2011, 2:32 AM   #3
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oh, so its not about the cam, its more about the lens. the lens should let in a lot of light.

does someone know which (affordable) lens would fit to my cam to realise this or which specification the lens needs to do this?
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Old Nov 18, 2011, 8:40 AM   #4
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Depth Of Field is controlled by 4 factors.
  • Lens focal length
  • aperture size
  • sensor size
  • distance to subject.

The longer the lens and the wider/bigger the aperture and the closer the distance all work together to set a shallow depth of field.

This site will let you calculate the exact DOF for any camera / lens / aperture / distance combination

From it I get these numbers for a 80mm lens and your camera.
On your body a 80mm f/4 lens at 24 inches will get about 0.24inch of sharp DOF
same lens at 36 inches to subject will give about 0.56 inch of sharp DOF

A 80mm lens at f/2.8 at 24 inches will give about 0.17 inch of sharp DOF
and at 36 inches it will give about 0.4inch of sharp DOF

An issue is many lenses will not focus that close.without extension tubes unless it is a specialized macro lens.

Note that:
Your 40-150mm set at 150mm @ f/5.6 and focused at 120 inches (10 feet) will get a DOF of 2.62 inches,
and focused at 60 inches (5 feet) gets a DOF of only 0.62 inch!

I would look into obtaining a set of extension tubes for your system if they exist.
These fit between your lens and camera and allow you to focus closer than normal.
They are usually much cheaper than a lens with a wide aperture.

These numbers show the area of sharp DOF, sharpness falls off gradually as you move away from the area focused on, it is not an instant sharp/blurred boundary.

Imaging is all about light and your ability to sculpt it.
Equipment is just a secondary nuisance.

Last edited by PeterP; Nov 18, 2011 at 8:56 AM.
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Old Nov 18, 2011, 10:05 AM   #5
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Originally Posted by PeterP View Post
Note that:
Your 40-150mm set at 150mm @ f/5.6 and focused at 120 inches (10 feet) will get a DOF of 2.62 inches,
and focused at 60 inches (5 feet) gets a DOF of only 0.62 inch!


These numbers show the area of sharp DOF, sharpness falls off gradually as you move away from the area focused on, it is not an instant sharp/blurred boundary.
If what you want to do is have something in sharp focus, the depth of field Peter quotes is the relevant fact. But, when you want to have a nicely-blurred background, the qualitative aspect in the last sentence is the real point. You may have something with a DOF of two inches where the background is still too much in focus at ten feet.

Further, the notion of "bokeh" is relevant here. OOF backgrounds are often objectionable because of the astigmatism of the lens, even if you would be perfectly OK with how OOF the background is otherwise. So looking at the DOF will only get you so far in evaluating whether a given lens is what you want for your photography. And, in my experience, bokeh is really hard to evaluate. Sample photos are less helpful than you would think -- bokeh is heavily dependent upon the color of the particular background, how far back the OOF object is, etc. The other very common thing to look at to evaluate bokeh is the MTF graph for a lens. The "gotchas" with that are first, AFAIK only Canon and Nikon actually provide MTF graphs any more. And second, MTF graphs are only loosely correlated to bokeh in my experience (although maybe I'm just not good enough at reading them.) My own experience is that even such objective points as the number of blades on the aperture are not as helpful as you might think. A curved 7-bladed aperture on a lens with low astigmatism might well blow the doors off the bokeh of a 9-bladed aperture lens with trickier astigmatism. And the problem is location-dependent -- if the corners of the photo have OOF objects that are tricky in this regard, the whole photo may look like crap, whereas a virtually identical photo that doesn't contain those corner elements might make the same lens look like a winner.

It is perfectly reasonable to want a good portrait lens, but deciding what that is is very hard. The Nikkor 70-200 f/2.8 VRII that TCav suggested is widely appreciated for portrait work, but it is a very expensive lens. The Nikkor 24-70 f/2.8 is also well-regarded for this work, but again it is quite costly. I use the Tamron 28-75 f/2.8 as my main lens for general photography and portrait work, and like it a lot. However, it does not have the best bokeh (although it is not bad) and f/2.8 is about as stopped down as you would often want to go in portrait work. Fortunately, the Tamron is very good wide open, so f/2.8 is quite usable with that lens.

Most of the primes in the 80-120 range are often suggested for portrait work. I have the Tamron 90, which is highly regarded by some for that purpose. I think the bokeh is wonderful on that lens, but it really isn't my favorite for these things.The lens has a bit of a back focus issue and has serious LoCA in many contexts that drives me crazy These decisions are so individual that it is really hard to make recommendations that other people will be pleased with. When it comes to portraits, it seems that the range of what people look for in a lens is even wider than with lenses generally.

All of which is a long way to go to say that I can't offer any advice worth taking on this subject...

Last edited by tclune; Nov 18, 2011 at 10:12 AM.
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Old Nov 18, 2011, 10:53 AM   #6
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As you are interested in portraits, the Depth of Field is just one of the issues you have to deal with. Another is the Angle of View. To get the same angle of view as an 85mm portrait lens on a 35mm camera, you will be using a focal length of 42.5mm. The DOF at this focal length will be more than it would if using the 35mm camera. This is why TCav mentioned positioning your subject with more distance to the background.
Portrait photographers will often focus on the eyes of the subject in order to get the nice 'sparkle' effect from reflections, and to more evenly center the DOF. With the 4/3 sensor, you may want to try focusing on the tip of your subject's nose, to bring the sharpest part of the photo nearer the camera.
Usually, there is more than one way to accomplish the effect you want to achieve, so a combination of these techniques should work.

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Old Nov 18, 2011, 11:36 PM   #7
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exact depth of sharpness
ain't no such thing as "exact depth of sharpness"

As many folks have said it depends on many physical things like distance, focal length, ... Beyond the circle of confusion, it also depends on the viewing distance, subject (fog vs. butterfly wing), size of print/screen, ...

Exact just don't exist in all that.
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Old Nov 19, 2011, 2:49 PM   #8
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G'day Dex

Welcome to Steve's
As you say - you have a lot to learn & those replies above are starting to fill you in with the 'possibles' of it all

I do lots of portraits with my Panny 12x zoom camera. Here's one as a sample

Just an ordinary pic shot at 10x zoom, camera to subject distance about 2 metres, camera set to "A"perture mode at f5,6

If I came in closer to get just the face, then the background would be much more blurry

Hope this helps a bit with a practical example of what can be done
Regards, Phil
Has Fuji & Lumix superzoom cameras and loves their amazing capabilities
Google me at Travelling School of Photography Australia
Recent images at http://www.flickr.com/photos/ozzie_traveller/sets/
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