I definitely do not want you to go through the trail and error to figure out what it does. This is why I decided to write this post so after reading it you are going to instinctively know how to control DOF to the best of your ability.
To get started, below are some of the most common questions I’ve heard that will help you can understand this concept:
2) What is plane of focus in relation to DOF?
3) What is minimum distance in relation to DOF?
4) How does aperture affects DOF?
5) What is the circles of confusion in relation to DOF?
6) How to get star burst effect in your photograph with DOF?
7) Do you need expensive lens to get DOF?
8) THE 4 FACTOR THAT DICTATES DOF?
9) HOW TO GET THE MOST OUT OF DOF?
I highly encourage you to go through these step by step without jumping to the end (I know it’s temping). A lot of these are basic photography fundamentals but I have different points of view in some of them that are going to benefit you.
Enjoy! As always, I hope you learn a lot from this post!
What is Depth of field (DOF)?
A lot of people refer Depth of field (DOF) as bokeh. The term bokeh came from a Japanese word ‘BOKE’ which means blur or haze. In essence, photographers describe DOF as the out of focus portions of a photograph. For myself, this is partly true.
A more technically way to describe DOF in my opinion, is the measurement of quality of the blur on the background.
The thing is that not all lenses are created equal. Some lenses are going to perform better than others and create a higher bokeh quality. On the other hand, some lenses perform less as well but all lenses can create some kind of bokeh.
It is the measurement of quality of the out of focus area that defines DOF.
Overall, some photographers may define better DOF when using a Canon 85mm f1.2 because with the wide opening of the lens it produces dreamy bokeh. Others may also refer great DOF when using a 200mm lens shooting at f2.8 because of the long focal length.
Do not get trap into the mindset that you need expensive lens in order to get awesome DOF. I’ll explain more below.
Plane of focus in relation to DOF
When you focus on an object you created a plane of focus that is perpendicular to that object. Anything that goes to left/right as well as above/below is going to be in focus.
However, as you move closer into or further away from the object you started to create a 3-dimension plane that will make your picture goes out of focus. This is called tilting the plane of focus and is NOT something you want.
So, my best advice to you is that DO NOT TILT UP / DOWN, LEFT / RIGHT after you lock in your focus. The only thing you should do is to SLIDE. You can slide up/down/left/right however you want but do not tilt. This will ensure you not to get a blurry image after locking in your focus.
This happens a lot when I do portrait photography. If the model is facing away from me and has one side of his/her face towards me, the other eye is NOT on the same plane of focus and will get blurry when I take the picture. This is something to be extremely careful of when focusing with your camera.
Minimum focus distance in relation to DOF
As the term described, this is the minimum focus distance you can be to the object to get in focus with your lens.
Each lens has it’s own minimum focus distance and each type of lens is created differently. In fact, it is the manufacture’s business decision to make a lens minimum focus distance ‘closer’ than another lens.
Anyway, if you exceed the minimum focus distance (meaning too close) then your lens won’t be able to lock focus and you will get a blurry image.
This is why macro lens is built to shoot so close to an object. It has super close minimum focus distance so the object can get big in the shot to be ‘life size’ in the photograph.
Oh by the way, minimum focus distance is measured from the sensor of your camera NOT from the front of your lens. So you will need to take into consideration of your camera + lens length when measuring the minimum focus distance.
How does aperture affects DOF
As a quick recap, aperture is the same as f stop. When the f stop number is low (meaning a larger opening of the aperture blades inside the lens), the more light travel through the lens hence you can take picture in lower light condition.
On the other side, when the f stop number is high (meaning a smaller opening of the aperture blades inside the lens), the less light travel through the lens hence you need more light in order to focus probably to take the picture.
If this f stop numbering system is bothering you, think of it as a ratio. For example, f1.2 has a larger opening than f2.8 because 1/1.2 is larger than 1/ 2.8. The same goes vice versa.
Generally speaking, a smaller opening of a lens (higher f stop), the more depth of field you have in your shot (overall sharper image and less blur on the background).
The wider the opening (smaller f stop), the shallower depth of field you have in your shot (More blur in your image).
Circles of confusion in relation to DOF
This is the blurry light circles created at the background of a shallow depth of field photograph. Normally a wider opening lens the more circular sphere it gets.
A less expensive lens uses less aperture blades to create the circle so they create a less circular shape at the background.
Either way, you can get this kind of photograph with circles of confusion when shooting with low f stop putting the background out of focus.
Star burst in relation to DOF
Opposite to the above, you can capture star burst on any light that is not focused in the picture. You can achieve this by shooting at f16 or high fstop.
Do I need expensive lens to get great DOF?
Expensive lens do get the better DOF performance compared to other lens. But kit lens can get great result too! Many people think you can only get great DOF with a f1.2 or f1.4 lens. I totally disagree.
As long as you are close enough to your subject, and the background is far enough between your subject to the background, even a kit lens can achieve great DOF/Bokeh.
One of the greatest advantages buying a fast aperture lens though, is that you can always focus at the lens widest aperture. For example if you have a Canon 50mm f1.4 lens. When you focus the lens is going to focus using f1.4 all the time (even if you set it at f8). It will immediately switch to f8 as you press the shutter release button but when you are focusing it is at f1.4
Having this feature in the lens means you can focus faster in low light situation. So if someone is using a 50mm f1.8 lens right beside you focusing and you are using the Canon 50mm f1.4, your lens is going to focus faster in this situation. This is exactly the reason why photographers like prime lens that has low f stop.
The 4 factors that dictates DOF
2) Focal length of lens – generally the longer focal length you use, the more out of focus the background of your subject will get.
3) Focal distance to your subject – generally the closer you stand to your subject, the more out of focus the background will get.
4) How close the background and foreground are to your focus point – generally the further away your subject is to the background, the more bokeh you see on the background.
After you understood the fundamentals behind DOF, the 4 factors listed above should be a lot easier to digest. Remember, combine all 4 of the above to get the maximize impact of DOF. This applies to either end of DOF (extremely sharp or shallow DOF).
How to get the best out of DOF
– When posing a group of people, make sure the faces are lined up on the same focal plane.
– Always shoot wider when you have a group of people to get the maximum sharpness across all faces. You can always crop out later but you cannot fix a blurry image.
– To get maximum shallow depth of field (extreme bokeh) of your lens, get in as close as you can to the object physically and zooming in all the way. This is how even a kit lens can take professional pictures.
These are the core knowledge of DOF and I hope this post shed some light to get you understand this concept more. If you have any questions or want more this kind of topic please let me know. Keep your passion going photographers!