Depth of Field: Holy Crap, Batman!

[SoCal Steve]

Looking at some of my first 85mm f1.8 images and then the specs that came with the lense.

The Depth of Field numbers are scary low

Example: Focused at 8 foot at f1.8 it's in focus from 7' 10" to 8' 2".
Stopped down to f8 it only improves to a range of 7' 5" to 8' 8"
That's 4" in the first case and 15" in the second. (Rounded to the nearest inch.) Okay, 15" isn't terrible, but that kinda kills a lot of the benefits of a fast lense. No free lunches, huh?!

This makes focusing pretty darn critical. I'm almost afraid to use it for some available light wedding pictures I had planned for it.

Is there somewhere online where these DOF specs are available for other Nikkor lenses?

[Matt. K]

That shallow depth of field is the advantage of the lens. Pops the subject off the background.

[pippin88]

As I understand it, any 85mm lense will have that same DOF at those same numbers?

[SoCal Steve]

Thanks, Matt, I guess I missed the point.

Still seems hard to get a whole face in focus. A pair of them not at the same distance..... fahgetabowdet.

Is the 50mm f1.4 based on the same idea?

[Onyx]

Also beware this very shallow DOF when focus lock and recomposing - the slight panning of camera may result in a change of distance to subject and rendering an otherwise in focus image out of focus.

[MattC]

SoCal Steve,

DOF is the range of acceptable focus. There is only one point where the lens is truly in focus.
I use cards constructed from Thom Hogans DOF calculator bundled with his D70 eBook as a guide for each of my prime lenses. I am currently reworking them into a graphical format. I am yet to come up with one for zooms. There is this calculator online. http://www.dpreview.com/learn/?/Glossar ... eld_01.htm Note these are just guides. What is acceptable focus can be subjective, as is anything that may be published by Nikon.

Cheers

Matt

[SoCal Steve]

MattC -

Thanks very much!
That's a good Depth of Field reference and neat little DOF calculator.

SoCal

[MattC]

SoCal,

Check out how DOF is affected by different aperatures at very close distances (say 0.5m - I know... 85/1.8 does not focus that close). Paper thin for the most part no matter what aperature is used. As your distance to subject increases so does your DOF.

Cheers

Matt

[SoCal Steve]

I'll have to study some examples of how others have been using the 85mm f1.8.

Thanks to all for the help.

[Matt. K]

SoCal Steve
The 3 variables that effect DOF are focal length of the lens, f/stop and camera to subject distance. The 85mm lens will have less DOF than a 50mm lens. Camera to subject distance can result in a huge loss of DOF when you start getting very close to your subject. The 50mm lens may be more suitable for what you are trying to achieve because that 85mm is acting like a 120mm on your D70. Great for head shots but maybe too long for full figure shots unless you are outside and can get back a fair bit.