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

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

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: http://www.dofmaster.com/dofjs.html

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?

PicPocket Veteran Member • Posts: 3,865
Re: DOF for 50D w/ EF 100-400mm lens w/ 1.4X Extender

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: http://www.dofmaster.com/dofjs.html

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?

-- hide signature --
 PicPocket's gear list:PicPocket's gear list
Canon EOS 7D Canon EOS 5D Mark IV Canon EF 28mm f/1.8 USM Canon EF 85mm f/1.8 USM Canon EF 17-40mm f/4.0L USM +11 more
OP dukw_butter Junior Member • Posts: 34
Re: DOF for 50D w/ EF 100-400mm lens w/ 1.4X Extender

PicPocket,

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?

Thanks.

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: http://www.dofmaster.com/dofjs.html

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?

Karl Gnter Wnsch Forum Pro • Posts: 11,408
Re: DOF for 50D w/ EF 100-400mm lens w/ 1.4X Extender

dukw_butter wrote:

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.

It simply doesn't matter if a lens is an EF or an EF-S lens as this only affects the size of the image circle but the focal length is a physical measure of a lens design irregardless of the size of the image circle or recording media, so a 17mm EF-S lens has the same focal length as a 17mm EF lens!
--
regards
Karl Günter Wünsch

 Karl Gnter Wnsch's gear list:Karl Gnter Wnsch's gear list
Canon EOS 7D Mark II
Karl Gnter Wnsch Forum Pro • Posts: 11,408
Re: DOF for 50D w/ EF 100-400mm lens w/ 1.4X Extender

dukw_butter wrote:

PicPocket,

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?

Then you are suing a cheap teleconverter which is missing some contacts on it's bayonet. Don't expect any decent focusing from the combination...
--
regards
Karl Günter Wünsch

 Karl Gnter Wnsch's gear list:Karl Gnter Wnsch's gear list
Canon EOS 7D Mark II
Ian Worthington Contributing Member • Posts: 766
Re: DOF for 50D w/ EF 100-400mm lens w/ 1.4X Extender

An interesting question, but in a different way from the how the OP intended.

The dof is related to the f number, which is the ratio of focal length over the entrance pupil diameter.

As the tc goes on the back of the lens, the entrance pupil diameter won't be affected by it, only the focal length.

But Moose Peterson (I think) wrote that he finds adding a tc affects the dof, but not as much as the corrected aperture would indicate for the corrected focal length.

i

OP dukw_butter Junior Member • Posts: 34
Re: DOF for 50D w/ EF 100-400mm lens w/ 1.4X Extender

Actually, no, I'm not using a "cheap teleconverter". I'm using the Canon EF 1.4X Teleconverter II with a Canon EOS-50D and a Canon EF 100-400L IS USM. There's nothing cheap about what I'm using, IMHO.

Karl Gnter Wnsch wrote:

dukw_butter wrote:

PicPocket,

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?

Then you are suing a cheap teleconverter which is missing some contacts on it's bayonet. Don't expect any decent focusing from the combination...
--
regards
Karl Günter Wünsch

OP dukw_butter Junior Member • Posts: 34
Re: DOF for 50D w/ EF 100-400mm lens w/ 1.4X Extender

OK. Some of this stuff is sort of counter-intuitive. But I believe what you're saying. I'll just use the focal length printed on the lens to do my calculations. Thanks again.

Keyboard shortcuts:
FForum MMy threads