Pole Hole/Other DOF - Whacha think?

DGMPhotography · Dec 30, 2012

Hey, so I was trying to get some hokeh with my kit lens. Isn't super easy, but this was the best I could do at the time, at Belle Isle. What do you think of these photos?

jlo24141 · Dec 30, 2012

i like the last one the most

thetrue · Dec 30, 2012

I like the hydrant (?) the best, the colors are awesome and the DoF is splendid, making for some nice Bokeh.

o hey tyler · Dec 30, 2012

What you were trying to accentuate was "bokeh" not "hokeh." Having a shallow depth of field is inherently easier with a long focal length, and a large aperture is a plus too. Your depth of field will be shallower fully zoomed in with your kit lens than it would be at 18mm.

As for the photos... Well, you're new to photography, and probably this forum. So I'll keep it to myself. Keep shooting!

DGMPhotography · Dec 30, 2012

Sorry, hokeh was a typo. If you look, b is right below the h. I had my fstop as low as I could get at 3.5, but to do that I had to not zoom in, so what are you supposed to do? I've been doing photography for almost a year now, and if you look "I spend too much of my life on TPF!" so I'm not too new, but still warming up to the forum I suppose.

I'd like to know what you think of the photos- not telling me anything won't help me learn, but just be nice about it if at all possible!

KmH · Dec 30, 2012

Bokeh is not adjustable, but depth-of-field (DoF) is.

DoF is influenced by a number of factors:

image sensor size
Lens focal length
How far the point of focus (PoF) is from the camera
The lens aperture used
and how far behind the PoF the background is.

A kit lens mounted on a APS-C (1.6 crop factor) camera body, set to 18 mm, an aperture of f/3.6, and with a PoF 5 feet from the image sensor will deliver:
Total DoF - 3.49 feet deep
DoF starts - 1.2 feet in front of the PoF (34%). (3.8 feet from the image sensor)
DoF ends - 2.3 feet behind the PoF (66%). (7.3 feet from the image sensor)

Changing only the PoF distance - to 10 feet from the image sensor then delivers:
Total DoF - 21.1 feet deep
DoF starts - 3.9 feet in front of the PoF (18%). (6.12 feet from the image sensor)
DoF ends - 17.3 feet behind the PoF (82%). (27.3 feet from the image sensor)

Now lets consider what happens when a longer focal length is used.
We'll use a 1.6 crop factor image sensor, a 50 mm lens at f/4 and a 100 mm lens also at f/4.
We will keep our main subject scale in the image frame the same for both lenses, so we will use the 50 mm lens at 10 feet and the 100 mm lens at 20 feet.

For the 50 mm lens set to f/4 and a PoF of 10 feet we get
Total DoF - 1.84 feet
DoF starts - 0.84 feet in front of the PoF (45%). (9.14 feet from the image sensor)
DoF ends - 1 foot behind the PoF (55%). (11 feet from the image sensor)

For the 100 mm lens set to f/4 and a PoF of 20 feet we get
Total DoF - 1.83 feet
DoF starts - 0.87 feet in front of the PoF (48%). (9.14 feet from the image sensor)
DoF ends - 0.95 feet behind the PoF (52%). (11 feet from the image sensor)

Note that the 50 mm and 100 mm Dof is very nearly identical, though there is a signficant change in the DoF distribution that makes it closer to 50%/50%.

I used this online DoF calculator - Online Depth of Field Calculator
And recommend this tutorial - Understanding Depth of Field in Photography

DGMPhotography · Dec 30, 2012

Thanks! Bokeh is just how the particular camera handles out of focus areas, not the actual un-focusing itself. Perhaps I should have clarified that I knew that, but I will definitely look into that calculator and tutorial!

KmH · Dec 30, 2012

Bokeh is a property created by the design/construction of a lens.

The camera has nothing to do with bokeh.

A lot of people don't know that some of the lens elements in consumer grade lenses lenses are made of resin, not glass.
The number and shape of the lens aperture blades also influences bokeh.
Note that as lenses become more expensive, they also usually have more aperture blades, and that the aperture blades are also curved to make the lens opening as close to perfectly round as possible.