Question: > 
> **Possible Duplicate:**  
> 
> [Is there a 'rule of thumb' that I can use to estimate depth of field while shooting?](https://photo.stackexchange.com/questions/6047/is-there-a-rule-of-thumb-that-i-can-use-to-estimate-depth-of-field-while-shooti) 
> 
> 
> 

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: 
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.
> 
> 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.