# Patent: Canon 100-400mm f/5.6-7.1

#### Pape

##### EOS 7D MK II
Doubling the focal length does make a lot of difference to the depth of field. I am no expert in this area and may have it wrong. But, my understanding is the depth of field, all else being equal, increases linearly with f-number but decreases inversely with the focal length squared. So, if you double the focal length of the lens, the dof decreases by a factor of 4. Shooting a 1000mm lens at f/10 gives the same depth of field and subject separation as shooting a 500mm lens at f/2.5. Similarly, shooting a 400mm at f/5.6 gives the same depth of field as shooting a 500mm lens at f/8.75. But, it gets more complicated if you crop the shorter focal length image and view at the same size as for the longer. I think you then have to divide the dof by the crop factor. So, after cropping, the 1000mm lens at f/10 will give the dof of the 500mm shot at f/5. And the 500mm at f/7.1 will give the very close to the same dof and subject separation as a 400mm at f/5.6.

Take home message is that the 500mm/7.1 gives us croppers the same subject separation from background as a 400/5.6. Please correct me if I am wrong.

Edit SecureGSM posted just as I was posting and so it seems my maths is correct.
Hmm doesnt cropping give same dof ,unless you using lense what makes smaller image circle? =crop camera lense?

#### AlanF

##### Stay alert, control the camera, save photos
Hmm doesnt cropping give same dof ,unless you using lense what makes smaller image circle? =crop camera lense?
Hi Pape
I am talking about using different focal length lenses on the same camera and sensor, cropping and then looking at the output image at the same size, just as we do for our bird portraits. The image from the shorter lens will before enlargement have greater depth of field, but this decreases on enlargement. For example, consider blowing up a 4mmx4mm image crop from the sensor with a 400mm lens to full screen size and comparing it with a 5mmx5mm crop from a 500mm lens blown up. The part of the image that is perfectly in focus in the focal plane of the image will still be tack sharp in both when enlarged. The out of focus regions will become more blurred when they are enlarged. The 4mmx4mm gets enlarged by 1.25x1.25 more so the blurring gets worse.
I worked this out in my head this morning and have now found, as I expected, it is well known to the experts. There is an image of a golf ball in the middle of this link that shows how the dof appears smaller as an image is enlarged.
See https://www.bhphotovideo.com/explora/photography/tips-and-solutions/depth-field-part-1

#### Pape

##### EOS 7D MK II
Hi Pape
I am talking about using different focal length lenses on the same camera and sensor, cropping and then looking at the output image at the same size, just as we do for our bird portraits. The image from the shorter lens will before enlargement have greater depth of field, but this decreases on enlargement. For example, consider blowing up a 4mmx4mm image crop from the sensor with a 400mm lens to full screen size and comparing it with a 5mmx5mm crop from a 500mm lens blown up. The part of the image that is perfectly in focus in the focal plane of the image will still be tack sharp in both when enlarged. The out of focus regions will become more blurred when they are enlarged. The 4mmx4mm gets enlarged by 1.25x1.25 more so the blurring gets worse.
I worked this out in my head this morning and have now found, as I expected, it is well known to the experts. There is an image of a golf ball in the middle of this link that shows how the dof appears smaller as an image is enlarged.
See https://www.bhphotovideo.com/explora/photography/tips-and-solutions/depth-field-part-1
Ah yeah i am again messing things on my head

#### AlanF

##### Stay alert, control the camera, save photos
Ah yeah i am again messing things on my head
I've taught myself a lot from these discussions because I hadn't thought much about dof in the past. What's becoming more and more clear to me is that there are minimal disadvantages of a 500/7.1 vs a 400/5.6 and it puts more pixels on a kingfisher.

Quirkz and Pape

#### Pape

##### EOS 7D MK II
I've taught myself a lot from these discussions because I hadn't thought much about dof in the past. What's becoming more and more clear to me is that there are minimal disadvantages of a 500/7.1 vs a 400/5.6 and it puts more pixels on a kingfisher.
I doubt losing one stop never decrease resolution more than what extra 100mm gives more.And all bright days are just pure advantage.
Ok i guess there is one disadvantage ,birds looks bit more fat with 500mm ,but i doubt they come complain

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navastronia

#### dcm

##### Good or bad - it's not the gear.
This makes a lot of sense when you consider it from the intended M series user’s perspective (small/light) rather the a D/R series user wanting the same from an M series, but cheaper. Something has to give.

Could be an interesting compact lens when compared to the EF-M 55-200 f4.5-6.3 IS STM that I have, as long as they are able to incorporate IS (say in group L3). I’d definitely carry this over my EF 100-400 L or 70-300L when hiking with the M6II just for the size and weight savings. If I want to bring the big lens as I sometimes do, I’ll bring a bigger camera to go with it (D or R series).

Dragon

#### Dragon

##### EF 800L
here is Sigma 100 400 5 -6.3 at 400/F6.3.. 500 at F7.1 should give a similar look. see if you like it:

and here is more for your judgement:

Note that those first two links were shot with a 1.4 TC, so at least f/9. Just look at your third link and scroll down to find the pics with the mention of the 1.4 TC.

#### Dragon

##### EF 800L
This makes a lot of sense when you consider it from the intended M series user’s perspective (small/light) rather the a D/R series user wanting the same from an M series, but cheaper. Something has to give.

Could be an interesting compact lens when compared to the EF-M 55-200 f4.5-6.3 IS STM that I have, as long as they are able to incorporate IS (say in group L3). I’d definitely carry this over my EF 100-400 L or 70-300L when hiking with the M6II just for the size and weight savings. If I want to bring the big lens as I sometimes do, I’ll bring a bigger camera to go with it (D or R series).
I just ordered a Kenko HD 1.4 TC (that works with EF-s lenses) to put behind an EF-s 55-250m and in front of an EF-M adapter. That results in 98-350 with f/8 max, so pretty close to the discussed lens and the 55-250 is very sharp at the long end, so that combo should give a pretty good feel for the new lens. Given that the Kenko TC also works with standard EF lenses, it should produce almost a FF image circle, so the 55-250 with TC may work well on a FF body as well. At a minimum, it will be an interesting experiment for not very much investment.

#### Daner

##### AE-1 Program
Thinking of this as an EF-M 120-360 mounted on an M5 MkII (with IBIS, please!) would make it a compelling small and light long-reach companion to an EOS R with the RF 24-105L. That combination would hit a pretty sweet spot when it comes to price/weight/volume/IQ for travel and landscape work, especially for those of us who prefer to minimize the need to check bags when flying whenever possible.

I have demoed the 1DXIII and the EF 200-400 f/4 + 1.4x lens and loved them both. While that combination would be wonderful for riding around in a Land Rover on safari to shoot wildlife, I would not look forward to lugging it through airports or on any kind of extended hike.

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#### SecureGSM

##### 2 x 5D IV
Note that those first two links were shot with a 1.4 TC, so at least f/9. Just look at your third link and scroll down to find the pics with the mention of the 1.4 TC.
I have noticed that. however, at F7.3 depth of field is not much wider than at F9.0

#### Dragon

##### EF 800L
I just ordered a Kenko HD 1.4 TC (that works with EF-s lenses) to put behind an EF-s 55-250m and in front of an EF-M adapter. That results in 98-350 with f/8 max, so pretty close to the discussed lens and the 55-250 is very sharp at the long end, so that combo should give a pretty good feel for the new lens. Given that the Kenko TC also works with standard EF lenses, it should produce almost a FF image circle, so the 55-250 with TC may work well on a FF body as well. At a minimum, it will be an interesting experiment for not very much investment.
Follow up. I just tested the 55-250 with the new Kenko TC on a 90D and the result is not bad at all. The center is not quite as sharp as a 70-300L, but with a TC, that is no surprise. It is, however, quite decent even on the 90D. The edges have some CA, but that seems to clean up pretty well in LR. Magnification is only a little more than the 70-300L (maybe 320mm), so the 55-250 looks like it really tops out at about 225. Also just checked it on the 5DSr and it seems to provide almost a full image circle with a bit of vignetting in the very corners. I will try the combo out on an M5, but no reason to believe it won't work well and as a proof of concept for the lens under discussion, the answer is basically, I would buy the new lens in a heartbeat for my M kit.

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