Understanding DOF with different lenses

paddler4 wrote in post #14928284
yes, you can get the same DOF with a different focal length by adjusting distance to subject. Play with this: http://www.dofmaster.c​om/dofjs.html

This isn't true.

A long telephoto lens can give a much shallower depth of field at a much greater subject distance than a shorter focal length lens.

PUREBRAD,

While the second line of your response is true, so is the quote from Paddler4. You are raising a different aspect of DoF. Distance to the subject is crucial, the smaller the focal length, the closer one needs to be, until it gets ridiculously close in some cases. Equally, the subject to background distance has a big impact.

It is certainly easier to control DoF for a blurred background with a moderate telephoto.

Wilt wrote in post #14939433
Unfortunately not compatible with all versions of Windows...

http://www.bobatkins.c​om …okeh_background​_blur.html

Awesome. That's what I'm talking about.

Runs fine in Linux and FreeBSD using wine here.

PUREBRAD wrote in post #14940494
This isn't true.

A long telephoto lens can give a much shallower depth of field at a much greater subject distance than a shorter focal length lens.

You obviously didn't take the time to play with the DOF calculator!

Assuming f/4 on the lens mounted on APS-C format body, and 20/20 vision acuity of the viewer...

• object at 10', captured by 30mm lens in frame area of 5x7.5' with DOF zone of 1.8'
  
• object at 20', captured by 60mm lens in frame area of 5x7.5' with DOF zone of 1.79'
  
• object at 40', captured by 120mm lens in frame area of 5x7.5' with DOF zone of 1.79'
  
• object at 200', captured by 600mm lens in frame area of 5x7.5' with DOF zone of 1.79'
  
• object at 400', captured by 1200mm lens (yes, they do exist!) in frame area of 5x7.5' with DOF zone of 1.79'
  

Put two identical bodies sitting side by side on tripods, one equipped with a 50 mm lens, the other with a 600 mm lens, and focus and aim both at the same object with the same f/stop.

When the image from the 50 mm lens is cropped to the same size as that of the 600 mm lens, the only differences will be in the resolution and the bokeh. The DOF and perspective will be the same.

What fools people is that with a longer lens, we tend to shoot farther away from a subject than with a wider lens.

It is the camera to subject distance and f/stop that affect perspective and DOF, not the focal length.

Glenn

Glenn NK wrote in post #14941986
Put two identical bodies sitting side by side on tripods, one equipped with a 50 mm lens, the other with a 600 mm lens, and focus and aim both at the same object with the same f/stop.

When the image from the 50 mm lens is cropped to the same size as that of the 600 mm lens, the only differences will be in the resolution and the bokeh. The DOF and perspective will be the same.

What fools people is that with a longer lens, we tend to shoot farther away from a subject than with a wider lens.

It is the camera to subject distance and f/stop that affect perspective and DOF, not the focal length.

Glenn

The above idea is illustrated in a "sticky" (found in the General Photography Talk forum) tutorial titled Perspective Control in Images - Focal Length or Distance?.

SkipD wrote in post #14942036
The above idea is illustrated in a "sticky" (found in the General Photography Talk forum) tutorial titled Perspective Control in Images - Focal Length or Distance?.

Thanks Skip.

It seems that no one reads them (or understands or believes them) - otherwise this wouldn't be beat to death so often. And there wouldn't be so many erroneous statements about it.

Over on another forum, they are debating ETTR - some actually suggesting that one should expose to the left.

Glenn

Glenn NK wrote in post #14942071
Over on another forum, they are debating ETTR - some actually suggesting that one should expose to the left.

With today's political zoo, I try to stay in the middle.

uOpt wrote in post #14941680
Awesome. That's what I'm talking about.

Runs fine in Linux and FreeBSD using wine here.

I use this one for Windows. Infinity blur disc or POI blur disc are the values to look at.
http://toothwalker.org​/optics/vwdof.html

The rule of thumb for an object beyond the point of focus is that the blur disc for the OOF point will be the infinity blur disc size times the ratio of dist between OOF point and focus point and the distance to OOF point.

And infinity blur disc size increases with focal length, aperture, and closeness to subject. You have to halve the f/stop (2 stops) or focal point to double the infinity blur disc.

Hi there. I love this discussion. I thought I would point you to an exercise I posted on my blog with some different focal lengths.

http://www.megbitton.c​om/blog/?p=406

Have a great evening!

Meg Bitton wrote in post #14952682
Hi there. I love this discussion. I thought I would point you to an exercise I posted on my blog with some different focal lengths.

http://www.megbitton.c​om/blog/?p=406

Have a great evening!

Very well done. Really drives the point home that the classic "DOF" value really doesn't tell you much about how "readable" the background stays.