More bokeh? 200mm @ f/2.8 or 100mm @ f/2.0?

[Daniel Browning]

Which would have more bokeh (granted you had the same framing)?

The 200mm f/2.8 will have more out of focus blur, but the 100mm f/2 will have thinner DOF. The amount of the difference for the background blur will depend on how close you are to the hyperfocal distance. The reason why the 200mm f/2.8 has more blur even though it has a slower f-number is because it has higher magnification.

For example, using 35mm and h/CoC=1440 (CoC=0.025mm):

100mm f/2 @ 3 meters: 84mm DOF
200mm f/2.8 @ 6 meters: 118mm DOF

You can see the 200mm f/2.8 DOF is 40% deeper when framed the same way. Even so, it has more OOF blur.

(By the way, bokeh is not the "proper" term for this, because it only relates to the quality of the out of focus blur, not the quantity.)

[powers_brent]

Thanks guys. I was excited to see so many replies by only 930am! So just to make sure. To get the same framing for different focal lengths the subject distance is proportional to the focal length? (50mm-5ft, 100mm-10ft, 200mm-20ft, 300-30ft, and on and on (even in the reverse direction?)) And just to throw another wrench in the machine. I have the 100mm f/2.0 and the 300mm f/4.0. This is even another question, but I guess I can calculate it now for sure granted the subject distance assertion is correct.

[Daniel Browning]

To get the same framing for different focal lengths the subject distance is proportional to the focal length? (50mm-5ft, 100mm-10ft, 200mm-20ft, 300-30ft, and on and on (even in the reverse direction?))

Yes. There is a six-fold difference between 50mm and 300mm, so to get the same field of view (not angle of view), you need a six-fold difference in subject distance.

And just to throw another wrench in the machine. I have the 100mm f/2.0 and the 300mm f/4.0.

The 300mm will have slightly more diffuse OOF blur and deeper DOF. (When framed the same for distances far from the hyperfocal distance.)

Calculating OOF blur is much less common than calculating DOF. The only calculator I know of is Bob Atkin's:

http://www.bobatkins.com/photography/technical/bokeh_background_blur.html

I plugged in your numbers and used a 2 meter focus distance and typical 35mm 8x10 CoC values:

[Jon Ruyle]

Calculating OOF blur is much less common than calculating DOF. The only calculator I know of is Bob Atkin's:

Interesting, but... does he say *what* he is calculating? How does he define OOF blur? Do all these numbers come together to make a single measure of bokeh?