Depth of field

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thesmileyone

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John
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I think I am pretty good at guessing what F number i need for depth of field however I do need a little help.

When I want shallow depth of field or selective focussing I use F1.8 when stood a fair bit back, F2.8 (sharper) or F4. All on a nifty fifty.

However when i want to say, shoot the full body of a model in the woods, I cant work out what F number I need. I tend to shoot at F8 and then take the same shot at F11 and then take one at F22 just to be sure I have the full body in focus.

How do you work out what F number you need for deep depth of field without doing what I do ?

Also, your supposed to focus on models eye right!? How do you know which eye ? And if your shooting a pair of people, whos eyes do you focus on, the guy on the left or the girl on the right (if you want them both in focus and bokeh background) ? And which of their eyes? And how is it their feet stay in focus but the ground they stand on doesnt (this is good, but how do you do it ?)

Thanks!
 
You need to understand depth of field. It is affected not only by f/number, but also the size of the image (magnification). The bigger the image, either by moving closer or using a longer lens, the less DoF you've got.

It's also affected by the size of the sensor, which in turn affects the lens you need and the distance you need to shoot at, but since the sensor is fixed, we'll leave that for now.

Everything you need to know is here www.dofmaster.co including a handy calculator. Have a look there, and then come back with any questions.

Focusing on the eyes is usually favourite, and the nearest eye if that's critical. If the subject's feet are at the same distance as their eyes/face then they will also be in focus too. Again, once you've got a bit more underwstanding of how DoF works, it will all fall into place.
 
Sam-D said:
What’s wrong with using the depth-of-field preview button?
Sam-D
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Very hard to see anything very useful that way. But shooting a snap and checking it out by zooming in on the LCD, if you have a decent one on the camera, works okay with a bit of experience.
 
Sam-D said:
What’s wrong with using the depth-of-field preview button?
Sam-D
Click to expand...


Yeah not something I ever use. Just make sure you have enough DOF, I try to stick to f5.6 for more than one person up to f11 for a group. If I need/want to shot wider people need to be in line and I just check the LCD to make sure I got it.

You can shoot wide, say 1.4 on a single person but DOF will be so shallow I focus on nearest eye. If there head it turned even slightly every this else will be out of focus.
 
I get the exposure nailed every time as i use auto ISO upto 1600 with minimal, if any noise. (D300s).

But i want to try my hand at film (by using either the d300s or a light meter for metering) and then bracket around what they tell me untill i can nail exposure.

I dont have an issue with the shallow side of things its just more the deep side of things, most of my images have turned out well as if it goes wrong i can blend exposures from the F11 onto the F8 for example.
 
thesmileyone said:
I get the exposure nailed every time as i use auto ISO upto 1600 with minimal, if any noise. (D300s).

But i want to try my hand at film (by using either the d300s or a light meter for metering) and then bracket around what they tell me untill i can nail exposure.

I dont have an issue with the shallow side of things its just more the deep side of things, most of my images have turned out well as if it goes wrong i can blend exposures from the F11 onto the F8 for example.
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Well in the film days I would just use the same rule of thumb for DOF, I wouldn't push the shallow DOF quite so much if I was worried but don't forget acceptable sharpness will also depend on the final print/viewing size and some images that might seem a little soft at 100% will be fine.
 
Heres a perfect example of the sort of depth of field i want.

The two people are quite far apart aswell...where would you put the focusing point and what aperture would you use ?

207544_890752976731_1681_41565656_4768075_n.jpg
 
Both those subjects are in focus because they are in the same focal plane so you can focus on either person, the aperture will depend on the focal length, best bet would be to use a dof calculator as linked above.
 
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thesmileyone said:
Dofmaster.co doesnt work, and you cant take it with you to the shoot, can you!?
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Sorry, my typo, try this www.dofmaster.com

And yes you can take it with you. You can print out tables, download a mobile app, or even print out a neat custom calculator. All from that site (or numerous others).

But what you really take with you is an understanding of the things that affect DoF, coupled to some experience.

Start with these two factors to help get a grip on what's going on - f/number and magnifcation (the size the subject appears on the sensor).

Low f/number = less DoF
High f/number = more DoF
Move close, longer lens, subject is magnified = less DoF
Move back, wide-angle lens, subject is less magnified = more DoF

Edit: crossed post with Terry
 
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thesmileyone said:
Heres a perfect example of the sort of depth of field i want.

The two people are quite far apart aswell...where would you put the focusing point and what aperture would you use ?

207544_890752976731_1681_41565656_4768075_n.jpg
Click to expand...

Impossible to say what aperture was used - this will vary depending on lens and sensor and other stuff - but probably quite a big one; f/2.8, say. Focus lock is likely to be the the simplest way to get both main subjects in focus. Select centre focus point, focus on one of the subjects, half depress shutter to lock, then recompose and I'm sorry if that's a bit obvious - I'm new here and don't know many people yet :)
 
Personally, I just go by my gut feeling and don't rely on DoF table and charts. I know if I shoot wide open (be it at f/1.8 or f/2.8) then there's going to be much more chance of not getting things nailed, so I generally stop down a tad without losing too much OOF. I know on my 50mm (or the 17-55mm at 50mm setting) that if I'm shooting a full body, f/4 will pretty much give me what I want but then I have to figure in how it'll affect the overall exposure in terms of a balancing shutter speed, ISO, and if using flash, how much flash to use.

I wouldn't worry about focussing on eyes when you're doing a full body; pick a point on the subject that you know won't move freely (torso as opposed to hands), making sure it's in a plane that pretty much runs throughout the shot so you get the face sharp also.

I'd say that if you want to really maximise the potential for bokeh and blur, use a longer lens; you're on DX so something like an 85mm lens will instantly provide you with more subject/background seperation at the same f/number, but you'll have to step back further to get the same composition.

You also need to think about subject to background distance. Even at a high f/number like f/11, you can get at least some background blur if the background is far enough back. Those DoF tables and charts help in this situation but again, experience will speed things up and unless you can measure distances, they're not going to work 100 per cent effectively for you.

I don't know how everyone else focussing, be it centre point with AF lock, using the outer AF points, or doing it manually; each to their own in reality. I tend to use more than the centre AF point if I want to work quickly, reverting to centre point with AF lock to recompose when I have more time with a static subject. The risk of using AF lock is, arguably, when shifting the lens you're shifting the plane of focus so it may not then have what you want in focus. This is probably a point of argument in itself as to whether that's strictly true but it'll about about how you feel comfortable and confident and if that's done by using the whole of your AF system, then do that...

For the shot of Obama above, I wouldn't imagine the photographer was any closer than 20ft, judging by the heads in the rows in front and the fact that there may have been a request for photographers not have been been 'in his face' so to speak. For me, the key thing to getting a shot like that is the decision as to how much you throw the faces of the crowd (facing you) out of focus; without any clear dicstintion of their expressions then they're just blobs in the distance. Equally, if they're too sharp then you lose the seperation between background and speakers....
 
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Think of DOF as a hollow wall that's parrallel to the camera's sensor. As you know the lower the f/ number the smaller the DOF. In wall terms, it's a very thin wall, but everything between the bricks will be in focus accoss the frame. As you raise the f/ number you are making the wall thicker. At say f/11 you can fit a whole person between the wall, but at f/2.8 only a small part of their body will fit in.
 
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