Depth of field, one of those things we learn about at the beginning of our 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 because it is little understood.
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
PICTURE #2
Important hints:
- I did not change focus points
- I did not change physical distance
- I used NO photoshop magic to change the blur on either photo
- I used the same camera for both photos.
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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 4 other forums just to get some reactions and numbers. The facts are that if you were the same as the other forums, 80-85% of you made the wrong choice. :)
Kinda backwards, huh?
Let's look at this a little... how do we control this DOF (or blurred background) thingie? Well to know that, we have to understand the control points of what produces a blurred background.
These five items are:
- Ratio of distance from camera to subject vs distance of camera to background (thats two)
- aperture
- focal length
- sensor size
Everyone seems to know about the aperture, some knew about the focal lengths and some knew about getting close, but apparently, very few people know all 5 control aspects of how to blur the background.
Ok, so if you asked me to blur the background, what would be the 5 ways I could do it?
Well...
- First is to get closer to your subject. Closer = shallower DOF.
- Second is get your subject and the background farther apart. Further background from subject = shallower DOF.
- Third is aperture. Bigger aperture (smaller numerically) = shallower DOF.
- Fourth is focal length. Longer focal length = shallower DOF.
- Sensor size. The bigger the sensor, the shallower the DOF will be for any of the 4 above given constraints. An FX sensor will have shallower DOF than a DX... and a 4X5 camera will have a shallower DOF than a FX sensor, etc... The bigger the sensor, the shallower the DOF.
Obviously, if you want LESS background blur or a greater depth of field, just reverse any of the above 5 points.
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 so that it was framed 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 except for the stitching (which had no bearing on how much blur there was in the photo)!
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.
