# What's the furthest you should stand with a 35mm lens at f1.8?

I understand the principles of depth of field, but am unclear as to what the recommended further distance is when you want to use a lower f stop. Surely at some point, your subject will go out of focus and you should then go to a higher f stop #?

• You may want to take a look at How do you determine the acceptable Circle of Confusion for a particular photo? – dpollitt Nov 26 '15 at 16:43
• IMHO this is too complicated. If your subject goes out of focus, you should refocus. All these calculations that you can do around DOF and aperture are "theory". This is necessary to understand the principles. To take a good shot, it is usually best to just focus and shoot. The subject needs to be in-focus. The discussions around DOF are anyway dependent on POV. – user23573 Nov 28 '15 at 13:26

I think your understanding of Depth-Of-Field (DOF) needs some clarification:
We can sharply focus our camera on a subject regardless of camera to subject distance (super close distances fall under special circumstances). If our subject is a person we likely focus on the eyes. If no DOF existed, the eyes would be sharp and clear though the nose and ears would be out-of-focus. The fact is; a zone exits before and after the point focused upon that images with reasonable focus. This is the span we call depth-of-field.

The span of acceptable focus is not split down the middle; it extends 2/3 to the rear and 1/3 back towards the camera. For example: Subject at 8 feet, aperture f/11, zone of DOF 6 feet thru 15 feet.

We can expand the length of the zone of DOF by:
a. Using tiny diameter apertures like f/11, or f/16 or f/22
b. Causing the subject to camera distance to increase
c. Mounting a short focus (wide-angle) lens

We can diminish the length of the zone of DOF by:
a. Using large diameter apertures like f/1/4 or f/1.8 or f/2
b. Placing the subject close to the camera
c. Mounting a longer than normal focal length lens

Related to DOF is a topic called hyperfocal distance: We can consult tables and charts that give the span of DOF for every distance and aperture setting. Likely these same tables will give the hyperfocal distance settings. The hyper focal distance is commonly used by landscape photographers and for those occasions when focusing the camera is a too time consuming or bothersome.

Setting the camera to its hyperfocal distance maximizes DOF. Say you find a table that tells you to set your camera at the hyperfocal setting ; focus at the 11 feet mark, set the aperture at f/16. Now your DOF will span 3 feet to infinity ∞ (as far as the eye can see).

• 2/3 DOF behind subject and 1/3 in front is a very crude rule of thumb, said for years, true maybe for full frame f/11 at 8 feet, but there are many other cases it is not very correct. Shorter distance or stopped down greater tends to approach half in front and half behind. But greater distances or shorter lenses or smaller sensors tend to extend it, often to infinity behind and only a few feet in front. DOF varies, any general rule is very crude. – WayneF Nov 27 '15 at 18:22
• Just wondering if you might have a link to a better quality picture of DOF, cant really read that photo. – thebtm Nov 27 '15 at 22:23
• WayneF -- As you know, DOF has many ingredients. At unity (1:1 or life-size) DOF is split down the middle. When we shoot, we almost never consult DOF tables. We need a rule-of-thumb to guide us. The 2/3 behind and 1/3 before rule is a good guide to follow. – Alan Marcus Nov 28 '15 at 0:22

Surely at some point, your subject will go out of focus

You focus on a point. The thing at that point is in focus.

Aperture affects depth of field, i.e. what stuff in front of your focus point and behind your focus point is rendered acceptably in focus. But the thing you have focused on is still in focus, regardless of your aperture setting and/or its distance from you.

The depth of field does indeed depend on focal length, distance to subject and aperture. It also depends, on a lesser degree, on how large you view or print your picture, and on sensor size. You can use a depth-of-field calculator to find the depth of field for a particular combination.

For example, using this calculator, I found that, assuming an APS Nikon camera and a subject distance of 10 feet, things will start to get out of focus at 11 ft from the camera.