School me on Bokeh. Pics included.

eric-holmes · Nov 11, 2009

Lately I have become more and more interested in Bokeh. I understand that if you have a wide aperture that you will have a shallower DOF. But I do not know about the focal length. I guess what I am trying to say is, Do I need to be closer to the subject with a shorter focal length? Or further away with a longer focal length? Or does it even matter? Here are a couple of pictures straight out of the camera. Keep in mind these are not meant to be interesting. Only for example.

itznfb · Nov 11, 2009

Online Depth of Field Calculator

dhilberg · Nov 11, 2009

Er, bokeh isn't referring to the out-of-focus area of a photo. Bokeh is the quality of the out of focus area. It's a common misconception.

The best way to evaluate "bokeh" is to have bright points of light in the out-of-focus area of a photo.

Ken Rockwell has a great write up on it:
Bokeh

eric-holmes · Nov 11, 2009

Ah, I thought bokeh was the term used for the OOF area as well. I was aware that you could have good and bad bokeh.

itznfb · Nov 11, 2009

dhilberg said:
Er, bokeh isn't referring to the out-of-focus area of a photo. Bokeh is the quality of the out of focus area. It's a common misconception.

The best way to evaluate "bokeh" is to have bright points of light in the out-of-focus area of a photo.

Ken Rockwell has a great write up on it:
Bokeh

It's actually both...

the word bokeh is the English translation of boke which means "blur". However in photography it's generally referred to as out of focus quality. Which I just looked up is boke-aji "blur-quality".

Big Mike · Nov 11, 2009

OK, you know that a wider aperture will give you a shallower DOF. Also, a longer focal length will give you a shallower DOF...and being closer to your subject will give you a shallower DOF. So it's a bit of a trade off with being closer and using a longer focal length.

As to the OOF areas, the distance from the focus point will affect how it looks. The farther away, the more OOF it will look. For example, something just out of the DOF will be just a little OOF...but something well behind (or in front) of the DOF, will be much blurrier.

DScience · Nov 11, 2009

I'm a bokeh addict. Check out my flickr if you want.

Another thing to keep in mind, is that different lenses render OOF light differently. Some produce more pleasing bokeh than others.

LuckySo-n-So · Nov 11, 2009

If YOU like it, it's good bokeh, if YOU don't like it, it's bad bokeh.

Stosh · Nov 11, 2009

I too was on a quest to find out how to get the most background blurs in different situations. It turns out that in the quest for blur, you can oversimplify by dividing into 2 type of blur: depth of field, and background blur. Most people concentrate on the depth of field which is almost entirely determined by f-number. As Big Mike said, moving closer gets you more blur (less depth of field), but you'd have to use a lower focal length to accomplish the same field of view. The lower focal length gives you less blur from a larger depth of field, so the distance and focal length issues almost exactly cancel each other out leaving f-number as the sole (almost) variable in depth of field. If you don't believe it (I didn't at first), use any online depth of field calculator. Make sure when you double the focal length, you also double the distance to subject to achieve the same framing of the subject. This will give you almost EXACTLY identical depths of field.

Turns out the blur we're mostly looking for is the background blur. "Background" can be loosely defined as anything beyond twice the distance from the subject to the camera. The easier way to think about it is that you have to be at least as close to the subject as the subject is to the background, preferably closer. The amount of background blur is determined by aperture, not f-number. Since most people confuse the 2, aperture is focal length divided by f-number. So a 50mm lens shot at f/2 has an aperture of 25mm. Larger apertures produce more background blur. Generally speaking, longer focal length lenses usually are capable of larger apertures than shorter lenses, but that's not always the case. For example, 300mm divided by 5.6 = 54mm, more than twice as much as the 50mm at f/2. You'll have to do the math with the lenses you have.

So one would deduce that you should always use your longer focal length lenses if they have the largest aperture. Not necessarily. The problem with this is if you choose a long focal length lens and you have to back away pretty far from your subject to properly frame it, you now risk having the background closer to your subject than you are. Now the background is no longer the background as defined above, and will now more closely follow the rules of the depth of field blur. This is a problem because most long focal length lenses do not have low f-numbers meaning there will be a deep depth of field, therefore ruining the blur you're looking for.

So to summarize you want to choose the largest aperture lens that still allows you to be as close (or closer) to the subject than the subject is to the background. That's how to get the most blur. If your background happens to be really far away, you can blast away with your long focal length, high aperture lenses. As others have said, bokeh is another subject altogether.

Derrel · Nov 11, 2009

Stosh is doing a fantastic job of describing the relationship between focal length and the camera-to-subject distance. His description of needing to move FAR AWAY FROM a subject when using a long focal length lens, thus causing an increased depth of field is a well-known issue,and that is perhaps *the* central problem in using an APS-C format camera to achieve shallow depth of field.

The easiest way to achieve a more shallow depth of field is to increase the size of the capture area. In other words, to step up to a full-frame sensor, which will allow you to use telephoto lenses with low f/numbers (like an 85mm f/1.2 or 85mm f/1.4 lens) from a distance of 20 feet, in order to frame a 6-foot tall man. Using an APS-C Canon, with a 1.6x FOV crop, to get the SAME field of view height, the camera must be 34 feet distant from the man. The depth of field differences are HUGE in this instance ,between the FF and the APS-C camera, using the same lens, but at widely different focus distances.

This is why wedding and portrait/advertising people flocked to 24x36mm digital capture as soon as they could afford to do so; the larger capture format allows 50,60,85,and 100 and 105mm lenses to be used at "traditional" working distances, to achieve shallow depth of field effects that are washed away when the capture size is dropped to 1.5x or 1.6x.

Hooker771 · Nov 11, 2009

DScience said:
I'm a bokeh addict. Check out my flickr if you want.

Another thing to keep in mind, is that different lenses render OOF light differently. Some produce more pleasing bokeh than others.

Ive added you as a contact on flickr. Love your shots and hope to learn a bit!

Stosh · Nov 11, 2009

I should have added in my above post that if it's impossible or impractical to get closer to the subject than the background is (like somebody in the middle of a crowded room), then forget everything about background blur and you're back to plan A which is depth of field blur where low f-number rules. In this case you would get out your 50mm f/1.4, or better yet your 85mm f/1.2, or better still a 50mm f/0.95!!!

LarissaPhotography · Nov 11, 2009

I've definitely noticed that what everyone was saying here is true, but it's nice to put some science behind it. Thanks to all you experts on blurring the background. The depth of field calculator is great. Added to my favorites.