11 replies to this topic

[Leaviathan]

I took this photo earlier today over looking the cape cod canal, the bridge is a couple miles away and that's what I was focusing on, shouldn't the brush right in front of me be more out of focus? The lens and camera were both in Manual Mode. This is about a 50% crop as I was using the 18-55 VR

 

[Dennis]

The short of it is; the field that will appear in focus is determined by; aperture, focal length and subject distance. For a given aperture and focal length, the farther the subject, the larger the field will be.

 

So, given your camera; with the subject being 10ft away

Depth of field  Near limit  8.99 ft Far limit  11.3 ft Total  2.27 ft

 

However, given the same setting, if the subject is 400ft away

Depth of field  Near limit  72 ft Far limit  Infinity Total  Infinite

 

72ft through infinity.

 

Hope this helps. I used this place for the general calculator: http://www.dofmaster.com/dofjs.html

[Leaviathan]

Ok, I gotcha, I shouldn't have been at f5.6 live and learn  That link is a great tool, thanks!

[Dennis]

Welcome

[james23p]

Excellent explanation Dennis well done. 

 

Nice shot by the way looks like a great place for a picnic!

 

Jim

[Leaviathan]

Excellent explanation Dennis well done. 

 

Nice shot by the way looks like a great place for a picnic!

 

Jim

The property taxes attached to those views are killer. It would be a lavish picnic 

[Sailjunkie]

Thanks for the link, Dennis. 

[ericbowles]

Generally you want to think about focus in terms of what you want to appear sharp.  If you want multiple elements of an image to appear sharp, you'll focus about a third of the way into the scene.  You'll also want to consider both aperture and focal length.  For a lot of the image to be in focus, you'll want to select a higher aperture - like f/11 or even f/13.  Focal length matters because with longer focal lengths, depth of field is shallower so you have less of the image in focus.  With a wide lens or low focal length, most of the image will be in focus even at f/5.6 if you focus on the right place.

 

In this specific image, you were at 55mm with a DX camera - an equivalent of 82mm.  It looks like the bushes are about 50 feet or so from the camera.  Assuming you wanted both the bushes and the bridge to be in focus, you'll need to focus on the bushes (there really are not many choices, but you could focus just past the bushes in a perfect world - maybe 65 feet instead of 50 feet - and the bridge would be more in focus.  If you focus on the bushes, you'll need an aperture of f/9 at 55mm.  If you reframed the image to a 35mm focal length, you could focus closer to the camera and have the entire scene in apparent focus - 36 feet at f/5.6 would work. And if you framed the image with to an 18mm focal length focusing on a foreground element 10 feet away, the entire scene would appear in focus at f/5.6.

 

As a practical matter, for landscapes I use f/11 as a starting point and adjust as needed.  I also try to focus on something relatively close in the scene - especially with wider lenses.  You are far more likely to naturally focus on something too far away than too close with a wide lens.

[Leaviathan]

The bushes were about 150 ft in front of me and the bridge a couple miles. I wanted the foreground to be fuzzy.

[Dennis]

Keep in mind that the 18-55 is basically AF long distances pretty near infinity. So, everything from closest focus to infinity will be in focus. So even wide open and setting AF manually, it is not going to produce the results your looking for.

Eric's method is also what I do.

[ericbowles]

With the bridge 2 miles away and the bushes at 150 feet, you'll need very different framing, gear.and composition to throw the bushes out of focus.  

 

I'd be thinking about a very fast long lens - something like a 70-200 f/2.8 at 200mm f/2.8, or possibly a 300mm f/2.8.  You would want to get closer to the bushes - within 50 feet - and you'd still be two miles from the bridge.  The problem with this setup is you will struggle to get the entire bridge in the frame.  So the alternative is to get even closer to the bushes and use a faster lens.

 

If you want something close to be out of focus, get close to the item you want out of focus and use a medium to longer lens.

[Dennis]

A 50/1.8 would be able to do it and be fairly inexpensive. But, you still need to be closer as Eric said.