How to estimate depth of field? [duplicate]

Question

Possible Duplicate:
Is there a 'rule of thumb' that I can use to estimate depth of field while shooting?

How do you estimate the aperture needed to produce sufficient depth of field for a given subject?

For example:
Suppose I am facing a bicycle from the front and use whatever combination of focal length and subject distance is necessary to have the bicycle completely fill the frame. I focus on the handle bars as I would like this to be the sharpest point of focus. How can I best estimate the aperture needed to ensure that entire length of the bicycle is within acceptable focus?

I have tried using my camera's DOF preview button, but the resulting image is too dark in the viewfinder to determine the depth of field.

I could use a DOF calculator, but this would take too long.

I could take a few shots at varying apertures, but again, this would take too long.

What methods do you use to visualise depth of field in situations like this?

Answer 1

Experience! Once you've taken enough photos at various apertures and distances, you will have the experience to get the DOF right on the first or second try, without having to measure distances or perform calculations. With an accurate enough estimate, bracketing should get you quickly to the right aperture. Many cameras offer auto-bracketing options, so if you're able to do a relatively accurate guesstimate, then you can fire off three or five bracketed shots with one press of the shutter button.

Until you have the experience, you're either going to have to make guesses and review the results in the viewfinder (my recommendation), or get out the tape measure and use a calculator if you really require precision.

Answer 2

DoF calculators are good for when you can take your time setting up a landscape shot (and if your lens has a focus distance scale), but for more dynamic situations there are general rules of thumb that can help you.

For wildlife or portraits, you should be fine pretty much wide open on a normal lens - about f/4-f/5.6 should be fine.

If depth of field isn't a major issue, say if your subject is against a wall or multiple subjects are all at the same distance from the camera, a general aperture of f/8-f/11 should be fine.

For situations like you describe in your question, I'd go for something like f/16 - but don't be afraid to go up around f/22 if you have the light to handle it. There's a lot of scare-mongering around the net that f/22 or similar will give you horrible diffraction, which simply isn't true.

One thing to be aware of is that as your apertures get smaller, you have to make sure you're getting a decent shutter speed to minimise blurring. This is especially tricky when you are trying to balance DoF with a fast shutter speed for subjects like cyclists - unless you have bright sunlight, you will probably have to bump up the ISO to compensate.

Answer 3

I would either stop down as far as I can get away with, or shoot and check the image on the rear LCD.

I'm sure there's an approximation of the DOF formula that's simple enough to do a quick mental calculation, after guessing your subject distance and reading the focal length off the lens, but it's important to understand that there's really only one plane of focus, i.e. one depth that is as sharp as possible, and a certain area either side which is merely "sharp enough".

DOF calculators rely on a standard definition for what it acceptably sharp *. The depth values given guarantee that anything in those depths will be "acceptably sharp". But what if your definition of what is acceptable differs? With high resolution digital sensors some areas within the accepted depth of field limits will be less sharp than others. By shooting a couple of test images you can quickly verify if the areas you care about are sharp enough for your standards of acceptability.

I've said this before on similar questions, but it's worth stating again why estimate when you can have the actual answer in front of you in seconds?

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* To be fair the standard definition is sensible as it's based on the angular resolution of the eye so it applies to printed images you have in front of you as much as it does to billboards, provided you view the whole image at once. This is not the only way to view images, however! Let's say you're selling the bike on a website and want to create images people can zoom right into to see the details. Now you might need those areas to be a bit sharper. In this case it's important not to rely too heavily on DOF calculations.

Answer 4

What methods do you use to visualise depth of field?

When I used a Nikon FE, I used to look through the viewfinder and press the "stop-down"/"depth of field preview (DOF)" button.

None of my cameras since have had one. It is certainly a feature I miss. Nowadays I mostly guess.