Thursday, September 27, 2012

A question about background bokeh


Teachers know that the best way to really understand something is to try to explain it to someone else.  In this post I am going to talk about photography terms like aperture, bokeh, and depth of field, on all of which I am NO authority, believe me.  But explaining it will help me think through it for myself.  At the end I will give links to people who are actually qualified to talk about such things.  You may want to skip ahead to that right now.  Especially if you want to know what aperture is, because I am not going to try to explain that one.

After my post about the farm, Kate (a.k.a. Givinya deElba) asked me this question:


I'd be interested to know what your aperture was for the pic of the beans?  

(I'm thinking she meant this one focused on the cute Maggie with the beans in the background


as opposed to this one of just the beans.)


Different to the one with Bethany and the eggs?  

(That's where you can tell Kate is from Australia.  
I love that I can hear her accent when I read what she writes.)


Different again to the cow and calf? I liked that the cow and calf had recognisable corn in the background instead of bokeh - 
I might have been tempted towards bokeh myself and missed the lovely farm-feel of the corn.

First of all, it was really sweet of her to assume that I approached the shot of the cows with informed intentionality.  Kate and I track really well with each other.  I ask her Photoshop questions, and she asks me photography questions.  We answer with lots of links to people who could tell you the actual answer, if you are at the point where you could understand them.  And then we do our best to answer ourselves.


So here's my attempt at an answer to why you can see the shape of the the corn behind the cow and calf, rather than the comparatively smooth bokeh (bow-kuh--background blur) of the same corn in this picture behind the cows and Bethany.  Photographers love blurry bokeh, and that's why Kate was pleasantly surprised by the corn in the cow and calf photo.

The short answer to Kate's question is that I was using my 50mm lens at f/1.8 ("wide open") aperture on all of the photos you see in this post.  That means there are factors other than aperture which affected the amount of bokeh.

DSC_0598 - Version 2

This is the original photo of the cow and calf.  I cropped it quite a bit above, but now you can see they are fairly far away.  I am standing at the fence that Bethany was climbing on.  I focused on the head of one of the cows.  The whole cows are relatively in focus.


In this subsequent photo (not cropped), the calf had kept walking toward me, and now is much closer so that she doesn't even fit into the frame.  She is farther away from the corn.  I haven't moved.  I focused on the eyes of the calf, and you can see that even her neck is somewhat out of focus.

The f/1.8 aperture is great for creating shallow depth of field (again refer to tutorials).  But the closer you are to your subject, the more you get the effect of that shallow depth of field.  So the same calf that was all in focus at f/1.8 farther away only has her head in focus at the same aperture close up.  The corn bokeh maintained more detail at the same distance from me when the camera was focused closer to the corn and farther from me.  When the focus was on the subject closer to me, the corn is farther away from the field of focus, and therefore more blurred.  

In review:  

close subject+far away background=more bokeh


Is all of that as clear as bokeh?

Two great tutorial series with all of the basics including aperture and depth of field:

Another really interesting related topic is lens compression--good tutorial here.

Now go take a picture with some nice, smooth bokeh!  Unless it is corn.  Then capture the corn.  :-)


StitchinByTheLake said...

Oh. My. Goodness. Maybe I should print this and reread, about a hundred times. I want to learn this, I really want to learn this. I need a new camera. I want one that talks to me and says this is the 50mm lens. This is 1/8f. Now do this. Do they make those? :) blessings, marlene

Skeller said...

:-) :-) :-) I just KNEW you and the 50mm were going to be a match made in heaven. And I was right!

Melissa Mae said...

Skeller, I knew it too and am so glad she got one!! Now, the rest is like listen to the teacher on Charlie Brown to me. One day it all come in "focus" but for now I can't make sense of all this bokeh stuff. Oh well.

Melissa Mae said...

Oh, and next time you visit your friend's farm... I might have to be REALLY rude and invite myself.... I'm in love.

Givinya De Elba said...

Thanks Tracy! I am much less further along in my photography than you, and I just assumed that there were different f-stops creating the different amount of blur in the background!

And actually, I did mean the picture of just beans (although the one with Maggie is beautiful too!) I noticed that all of them were in focus except the slight amount of blur in the top, and that's why I asked about the aperture. I couldn't get that shallow depth of focus with my lens - I can't go lower than f3.8 :-(

Tracy P. said...

Ah, you did mean only the beans! They are all in focus because I was shooting them straight on, and what you see is almost all one layer. If I had tilted the camera so that I was shooting them at an angle, some would have been closer to the lens and some farther away--only those where I fixed the focus would have been in focus--those closer or farther away than the focused area would have been a little blurred. The ones at the top of the image are down deeper in the basket, so they are a little out of focus.

A good experiment to try is with baked goods on a tray or plate. Cookies are my favorite. If you shoot straight down at the cookie sheet, all of the cookies will be in focus because they are the same distance away from the lens. If you get down on table level and shoot across them, the one you focus on, along with others the same distance away, will be in sharp focus. Those in foreground and background will be blurred. I bet it will even work for you at 3.8/f!

I highly recommend that you go to the 31 Days link, and check out the two aperture lessons and the depth of field lesson. She has diagrams that explain this perfectly. I have photo examples, but she shows you what is going on with the camera. I think you will find that 3.8/f is wide enough to get you some beautiful bokeh. Get as close as you can to your subject, with background as distant as possible.

Tracy P. said...

Melissa, I'm sure Peggy would welcome you!