DOF, the basics and advanced

[jerryph]

A little something that I wrote for you guys and gals that want to take your understanding of DOF to the next level.

Depth of field, one of those things we learn about at the beginning of our learning of photographic apprenticeship is both a very simple concept, yet when you *really* understand it, can be made into an interesting and more advanced topic with some very complex overtones.

I am going to try to take most, if not all of you through the journey of surprising you. It is a concept that is obvious, yet little known.

Let me start off by showing you two photographs, one taken at F/1.4 and the other taken at F/2.8. Your job is to NOT look below at the answer for a few seconds, but take a look at the two photos and tell me which photo is taken at what aperture.

PICTURE #1
http://farm4.static.flickr.com/3185/4630057973_08ed667486.jpg

PICTURE #2
http://farm5.static.flickr.com/4049/4630658404_71e701c647.jpg

Important hints:
- I did not change focus points
- I did not change physical distance
- I useed NO photoshop magic to change the blur on either photo
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.Hey no peeking!!
.Go back up and look again at those photos again!!
.Make your choice before moving down!!
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Ok, so let me first give the answer and then do a brief discussion about DOF that explains what I did and how. :)

The answer to the question of which photo was taken at F/1.4 and which was at F/2.8 is... photo #1 was at F/1.4 and photo #2 was at F/2.8! All that chose #1 were correct, but we will say that all people that chose #2, were a little bit unfairly tricked. I've posted this on 3 other forums before here just to get some reactions and numbers. The facts are that if you were the same as the other forums, 80% of you made the wrong choice. :)

Kinda backwards, huh?

Let's look at this a little... how do we control this bokeh (or blurred background) thingie? Well to know that, we have to understand the control points of what produces a blurred background.

These four items are:
- Ratio of distance from camera to subject vs distance of camera to background (thats two)
- aperture
- focal length

Ok, so if you asked me to blur the background, what would be the 4 ways I could do it?

Well...
First is to get closer to your subject. Closer = more bokeh.
Second is get your subject and the background farther apart. Further background from subject = more bokeh
Third is aperture. Bigger aperture (smaller numerically) = more bokeh
Fourth is focal length. Longer focal length = more bokeh.

The trick that I did for this shot was very simple (and yeah, I admit it was a trick... lol), I increased focal length (but stayed at the same physical distance from the subject) and used a F/2.8 lens. I went from the 85mm F/1.4 to the 200mm F/2.8.

"But, but... the aperture is bigger!" you say?
Yes it was, and here-in lies my trick... I was the same PHYSICAL distance from the subject in both cases but since I was at 200mm instead of at 85mm, my *APPARENT* distance decreased drastically, I was a LOT closer thanks to the higher levels of magnification the 200mm gave me vs the 85mm.

"But, but... if you did that, the whole photo won't fit on one picture!" you say?
Right again, so, what I did was take 24 shots instead of one... basically using the shallower DOF of the longer lens and then stitching the 24 shots together into 1 shot, and then cropped the shot similar to photo #1.

The result? A photo with the apparent focal length of an 85mm lens, but at apertures something closer to a DOF of F/1.0... lol

You guys can see now that I did not change focus points, did not change physical distance and use NO photoshop magic to further blur the F/2.8 image, it was literally all done in camera!

I had a shot where I simulated F/0.6 aperture levels of blur, and they were very cool, unfortunately, I deleted the folder by accident, but since I can recreate this anytime I want easily, I wasn't too concerned.

No fair you say? I agree, it wasn't but it was fun to learn about and at the same time, I introduced a concept and technique that is very interesting to you in a manner that anyone with even rudimentary photography skills can understand, and even use! :D

Now, you all know how to take your F/2.8 lenses... and turn them into F/1.0 lenses (if only in terms of DOF blur, NOT low light performance)! :D

I hope you had as much fun learning this as I had presenting it.

[mingkywingky]

Thank you Jerry for the presentation of controlling the bokeh. Yes, I was in those 80% who made a wrong choice:D
I like the basic concepts for DOF but the advanced one seems too complicated for me.
I don't have that kind of lens (mine are 18-55mm and 55-250mm) but I still have trouble to control the bokeh in Manual Focus (MF). Everytime I change the focal length, it won't focus anymore. I don't have a problem when I use Auto Focus (AF), the lens will focus perfectly no matter what the focal length is. But we are supposed to use MF...right? Funny thing is, if I go to AF first to focus, then go to MF, the lens will work the same as in AF. Do I have to do that everytime I do the shallow DoF? I'm worry that will break my camera :confused:
I'm sorry if my question is not relevant to your presentation.
Thank you:)

Tenny
Canon Rebel T1i

[trashytrucker]

...I hope you had as much fun learning this as I had presenting it.


Jerry,
Thanks for sharing that with us all. Keep posting and sharing.

Matt

[eyerkish]

Thanks for the lesson, Jerry. Much appreciated.

[jerryph]

Wow, I am so sorry that I missed this!!

Let me correct for that.


no matter what the focal length is. But we are supposed to use MF...right?
No, not at all. I used auto focus in all shots. I think you need to try this once and then it becomes clearer. :)


Do I have to do that everytime I do the shallow DoF? I'm worry that will break my camera :confused:

There is nothing to break... the next time I do this, I am going to try to have someone with a video camera around so that I can explain this visually. It's a little funny to see, and not a technique that many people use, but it is a tool to add to your kit for those times you want to do something like this.


Let me walk you through the process and you can do it with any lens, just for fun. This way, the hardest part is downloading a program that can stitch panoramas and thats all you need.

Picture #1:

Let's say you have a lens like an 18-200. Stand 25 feet away, and zoom the lens until the subject (lets say a model that has a LOT of room behind them, lets say at least 100 feet) fills the photo from head to feet. It will be at about 50mm focal length to be wide enough to get the entire model.

To make things easier, use manual mode and meter on the face of the model for the exposure. Focus on the eyes and recompose if needed. Aperture at this point is not as important because on an 18-200 lens, it gets smaller the more we zoom, but thats ok, trust me. Now take one photo... click!

OK, so now you have a photo and its time to go to...

Picture #2:
This time, do NOT move your model, YOU move close, lets say 10-15 feet and now you manually zoom your lens as much as it can. In my scenario, if I was using an 18-200, I zoom it out to 200mm. If you look into the viewer you likely see only a head, but we want the full body, so don't move, but...

Again, you are in manual mode... meter for the face. Now, focus on the eyes... now, TURN OFF the autofocus of the lens/camera, and take many photos, as many as 30-50 making sure you do not change the focus or exposure settings and that you get all of the subject "covered".

When you assemble the photos into 1 portrait, you will see that the combined photos will have an incredibly shallow DOF with a ton of blur. You can use Photoshop or Stitch-It or AutoPano or any other software that can stitch photos together. After they are all together you may need to crop it a little so that it is rectangular without edges.

It doesn't get any easier. ;)

Again, I apologize for totally missing the gist of your post. :o

Enjoy!