DOF for 50D w/ EF 100-400mm lens w/ 1.4X Extender

Started Feb 28, 2010 | Discussions thread
OP dukw_butter Junior Member • Posts: 34
Re: DOF for 50D w/ EF 100-400mm lens w/ 1.4X Extender


Thanks for your feedback. You mention that with the 1.4X extender on the 100-400 lens, what I have is essentially a "140-560mm f/6.3-8 lens". This makes sense, but I'm surprised that my canon camera frame (50D) still allows me to choose f/4.5-5.6. I'm guessing that it's really acting like an f/6.3-8 lens, but the camera just doesn't realize that I've actually shaved off one f-stop of light?


PicPocket wrote:
short answer:

use 560mm f/8 for the fully zoomed wide open lens. EF or EF-S does not matter. 17mm from 17-55 IS is same as 17mm from 17-40 L

when you are calculating the DOF, you should just use the focal length and F-number of the optics on front of your sensor. your lens + extender is an optical assembly of a 140-560mm f/6.3-8 lens. You don't have to account for sensor size because the calculator is doing that already

dukw_butter wrote:

I'm trying to do some Depth of Field calculations with a Canon EOS 50D with the Canon EF 100-400mm f/4.5-5.6 L lens with the Canon EF 1.4x II Extender. I'm using this online DOF calculator:

I select my Canon EOS 50D, but I'm not clear what to put in the for focal length. The website says to use the Actual Focal Length of the lens, not the 35mm equivalent. But they also indicate that this is because they're adjusting for the cropping factor of the sensor already. Assuming the instructions are correct, I would multiple 1.4X * 400mm = 560mm and use that as the focal length.

However, my concern is that I have no way to tell the calculations whether the lens is an "EF-S" lens (designed for the smaller sensor) or an "EF" lens (designed for a 35mm sensor). Because the 100-400mm lens is an EF lens (designed for a 35mm sensor), I'm not clear that putting in 560mm as the focal length will get me the correct DOF results.

Does anyone have any feedback on this?

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