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Image taken with the E-M5 fitted with a 45mm f1,8 lens

So often I read people "talking about" depth of Field (DOF) on forums making statements like, M43 sensor cameras cannot produce a proper DOF like full frame cameras can, plus plus plus. What is DOF and is it correct to say M43 sensor cameras cannot produce good background blur? You see guys displaying images trying to explain depth of field and when you look a little closer, then it is clear that the poster does not know either. How is background blur linked to DOF and can I achieve background blur with my M43 camera? I decided to write this short article, first to give a very basic explanation of what depth of field is, and secondly to discuss how to create a small depth of field or a good background blur.

What is Depth of Field (DOF)?

First, lets have a look at Depth Of Field (DOF). If you look at the above image you will see it has a clear focal point, blur in the foreground and blur in the background. Point B is the point of focus, Sharp and thus in Focus (Focal Point), point A is the start of the "in-focus" range and point C the end of the" in-focus" range. Before point A, and behind point C one can see the out of focus area or the blur range. The depth of field (DOF) range from point A to point C. Before and after the depth of field range, the image blur increase as a result of the increasing "out of focus". DOF therefore is that part of the image that falls between the points A and C and that is in focus. People generally refer to increasing or decreasing the DOF. It simply means we move point A and C further away from each other or we move them closer to each other.

Background blur is that part of the image behind point C which is not in focus. We as photographers are often more interested in background blur and less in DOF. I said often because this will be different for landscape and portrait photographers. In landscape photography we like to increase the part of the image that is in focus (DOF) and in portrait work we like to limit the in-focus range (small DOF) so that we can see a background blur. If I have a model with me I would place her in-between points B and C knowing that behind point C the "blur" starts.

See this article over at
DPReview on DOF. If you really want to see more in-depth theory on this subject get yourself a copy of the 123 eBook.

Depth of field is generally effected by
subject distance, aperture size and focal length. There are more theory behind DOF but for purposes of keeping this article "friendly" to the reader I decided to keep with the said three variables. If any one or more of these three variables change then the DOF will change. For those who want to play, you can create your own "test" studio at home to test for yourself how these three variables influence DOF.

How does DOF compare between sensor formats? Vincent Bockaert wrote in his book 123di.com "A smaller format has a smaller Depth of Field ….." Focal Length is the the one variable M43 sensors really "benefit" from most. The M43 sensor format use a 2 times FL multiplier to get the same 35mm FL equivalent, the APC sensor a multiplier of 1,6 times and the full frame sensor is @ 35mm equivalent and needs no multiplier. What does this mean in real life? You will adjust the focal length for each format differently on the lens to ensure that the 35mm equivalent are the same!!!

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Image taken with a E-P3 fitted with the 14 - 150mm zoom lens. (f5,6 / FL=300mm / distance 1,1m)

Trying to get exactly the same image (effect) using a M43 camera or a APC sensor camera or a full frame sensor camera could be difficult and the reason is there are more to DOF. Keep in mind we said that three things impact DOF, aperture (f-stop or what aperture opening used), focal length and subject distance. If you keep the subject distance the same at 1,1 meter and the aperture opening the same at f5,6 then the only other variable are the focal length. This is one part where the sensor size has most impact. To set them all to 300mm at 35mm equivalent I need to use each sensors unique multiplier when dialing in the focal length of each camera:-

- with the Canon 7D we need to fit a lens that let us have 187mm (187 x 1,6 = 300mm)
- with the Olympus E-M5 I had my 14 - 150 lens at the long end (150 x 2 = 300mm)
- with the Canon 5D we need a lens that let us have 300 mm (300 x 1 = 300mm)

The actual lens design determine the quality of the blur. Things like the number of aperture blades, the roundness of the aperture and the lens elements, all influence the quality of the blur. A good quality blur is typically soft and it moves gently away from the subject. Some lenses really have a busy type blur which is not pleasant to look at, I recall the first Olympus 50 - 200mm f2,8 lens had such a busy blur…..

Modern lens designs use 7 blade aperture arrangements and with older lenses one often saw 6 blade units. Today a lens with 6 blades are referred to as having a poor design. Reason is the photographic community generally accepted a 7 blade aperture unit as the norm for good quality background blur.

How can I increase the depth of field?

With the image below, I simply kept the aperture and the focal length constant and then stepped further away from my subject. Practicing working with the three DOF variables will improve your own DOF success rate. Here are a few more general rules you can keep with you:

- Increasing the Focal Length (FL) increases DOF and vice versa
- Increasing the aperture reduces the DOF and vice versa
- Reducing subject distance reduce DOF and vice versa

Another general rule I use is to have enough "space" behind my model. Keep in mind the change over to blur behind point C in the above image is not always instant and not the same from camera to camera. Generally having enough space (distance) behind the model will ensure the blur effect is stronger in the background. Therefore if you take a picture of somebody and you have something like curtains right behind the person then it will become extremely difficult to create a good background blur. Best would be to ask the person to move further away from the curtain…..

Below you can see the same image as above. All I did to increase the DOF, I moved further away from the subject. The result is you can see more are in focus.

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Image taken with my E-M5 fitted with a 14 - 150mm Olympus lens

Practical examples of creating background blur

My son is a professional photographer and he was over at our place with some of his equipment. He had his Canon 5D MKIII, full frame camera with him and I asked him if we could do a few quick images. He used his 70 - 200mm, f2,8 lens and I had my 14 - 150mm Olympus lens on the E-M5. We also tried the 70 - 200mm lens on my 7D plus I have a 55 - 200mm kit lens we tried on the 7D. Here are the settings we used:

Focal Length:
- E-M5 and 5D and 7D were all 200mm (35mm equivalent)

The subject distance were: (Tip - when you try this yourself, see that you have enough free space behind your subject)
- E-M5 and 5D and 7D were all 3 meter away from the subject

Aperture:
- 5D MKII were on f5,0
- 7D were on f5,0 (I took 2 images with the 7D)
- E-M5 were on f5,6 (the E-M5 were therefore in a small disadvantage)

Here are the images (keep in mind I show the background blur only and not DOF in these images):

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Image taken with the new Olympus E-M5

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Image taken with the Canon 7D fitted with the 70 - 200mm, f2,8 lens

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Image taken with the Canon 7D fitted with the 55 - 200mm kit lens

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Image taken with the Canon 5D MKIII fitted with the 70 - 200mm f2,8 lens

You can see the 5D MKII background blur are beautiful. At this point I cannot achieve that same quality with the lenses I have. I look forward to see the new 75mm, f1,8 Olympus lens in action. It will be interesting to see the Leica 25mm, f1,4 in action also. As you can see from the above examples the three basic variables I discussed in this article are not the only factors determining DOF or background blur. What we did discuss is enough to help you develop your own skills and to start experimenting with DOF. When you start doing macro work you will see how much more aggressive DOF can be……

At the time of writing this article, I did one final image of the same "model" using my E-M5 fitted with my 45mm f1,8 lens. The focal length as you know are fixed at 45mm or 90mm in 35mm equivalent terms, the aperture was set to f1,8. I had ample space behind my model . All left was to move forward and backward until I were able to frame the model nicely and the background blur were OK.

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At the time of re-writing this article I have added a 10 - 300 Lumix lens to my bag plus a 70 - 300mm Canon lens. I decided to ask the same model for a shoot and as you will see she agreed. See the shooting data below each image for more information. As you will see the E-M5 has absolutely no problem to create a lovely background blur. It all depends on what lens you use, the distance or space behind the model and the focal length you use. At one stage I were testing the 70mm, f1,8 from Olympus and were very pleased with the wonderful soft blur that lens were capable of.

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Canon 7D Image, f5,0 at ISO 200 and Tv 1/10 w camera on a tripod (70 - 300mm Lens @ 210mm)

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E-M5 Image, f5,6 at ISO 800 and Tv 1/40 w camera on tripod (100 - 300 lens @ 193mm)

It is true that one can say much more about DOF but for this article I decided to leave it at this as I think the reader can use the info in this article to much better master a good background blur. I also like to say thanks to all the guys at DPReview that took part in giving feedback and that helped getting the article to be of more value to readers. If you have any questions, please drop a message in the forum.

Siegfried