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Thread started 19 May 2010 (Wednesday) 17:47
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5D Mark II vs 7D depth of field

 
aboss3
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May 19, 2010 17:47 |  #1
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I'm considering selling my 7D for 5D MK II, and wanted to know if there's a huge difference in the shallow depth of field when going full-frame? Let's say if we take 50mm f/1.8 lens on the 7D vs 5D MKII, will there be a noticeable difference when shooting portraits?


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dmo580
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May 19, 2010 18:00 |  #2

Well remember that 50mm in a 7D is like an 85mm FF equivalent, so if you want the same perspective on the 5D as 7D with a 50/1.8 you will stand at different distances.

If you shoot from the same distance, yeah you'll get a slightly more than 1-stop difference (1.6x crop factor) in terms of bokeh.

Edit: WTf whas I writing. If you want the same perspective, you need to use different focal lengths on the two bodies. If you want a DIFFERENT perspective, then you back it up... LOL...

But the bottom line is if you use a 85 on crop and 135 on a FF, with the same composition and perspective (same distance), the FF camera will have a more than 1 stop advantage in DOF. So F/2.8 on the crop will have more DOF than F/4 on the FF. Only slightly though.


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WireWess
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May 19, 2010 18:04 |  #3

This is a nice test:
http://www.seriouscomp​acts.com …n-full-frame-vs-crop.html (external link)


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diabolus
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May 19, 2010 18:09 |  #4

Yes, you should see a difference. With the 5D2, you will need to get closer to your subject to get the same shot you would see on your 7D. This difference in distance is what will give you the shallower DOF on a 5D2.


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sportsshooter50
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May 19, 2010 18:18 |  #5

For a valid depth of field comparison between cameras (crop and full-frame sensors) you have to use the same focal length and set at it the same f-stop. The only variable would be the camera to subject distance. You'll have to step back farther with the crop camera to get the same size image. Therefore doing so increases the depth of field for the crop camera. Using a 50mm lens on one camera and a 35mm lens on the other camera doesn't seem like a good way to compare depth of field.




  
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SkipD
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May 19, 2010 18:43 |  #6

You must realize that the suggestions above to change the camera position when using the same focal length on two different format cameras will NOT produce the same image in both cameras. That's because changing the camera-to-subject distance will change the perspective and that could easily make a huge difference in the composition of the images.

The only depth-of-field comparison that makes any logical sense when using two different format cameras is to use focal lengths on both cameras that provide the same field (angle) of view and use both cameras from precisely the same position.

If you use a depth of field calculator such as DOFMaster (external link), you must enter several variables. One is the "circle of confusion" which is entered in DOFMaster by choosing the camera format. You also enter the focal length, aperture used, and distance to the sharply focused point (usually the primary subject of an image). Make sure that you use focal lengths for both cameras that will provide the same field (angle) of view such as 50mm on the APS-C format and 80mm on the so-called "full-frame" format.

I ran an example through DOFMaster. Assume that the subject (sharply focused plane) is at 20 feet from both cameras. Use 50mm on the 7D, set at f/8. Use 80mm on the 5D, also set at f/8. The images from both cameras will be framed the same.

The results are:

7D - depth of field is 17 feet (distance from camera from 14.6 to 31.6 feet)
5D - depth of field is 9.5 feet (distance from camera from 16.3 to 25.8 feet)

For those folks needing to understand perspective, please read our "sticky" (now found in the General Photography Talk forum) tutorial titled Perspective Control in Images - Focal Length or Distance?.


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xarqi
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May 19, 2010 18:50 |  #7

What a shambles!

dmo580 wrote in post #10212082 (external link)
Well remember that 50mm in a 7D is like an 85mm FF equivalent, so if you want the same perspective on the 5D as 7D with a 50/1.8 you will stand at different distances.

To achieve the same perspective, you MUST stand at the same distance. The same result would be attained by cropping the FF accordingly, and when this is done, the DoF will be identical.

If you shoot from the same distance, yeah you'll get a slightly more than 1-stop difference (1.6x crop factor) in terms of bokeh.

Yes, there is a difference in DoF in this case, but there is also a difference in the resulting image. There is no difference in bokeh.

diabolus wrote in post #10212126 (external link)
Yes, you should see a difference. With the 5D2, you will need to get closer to your subject to get the same shot you would see on your 7D. This difference in distance is what will give you the shallower DOF on a 5D2.

Again - if you change distance, you change perspective, so the results will not be the same. If you do change distance though, yes, there will be a difference in DoF, but that is true irrespective of what body is used.

sportsshooter50 wrote in post #10212168 (external link)
For a valid depth of field comparison between cameras (crop and full-frame sensors) you have to use the same focal length and set at it the same f-stop.

Good.

The only variable would be the camera to subject distance.

Not so good. For that comparison, distance must also be held constant. The only variable should be sensor size.

You'll have to step back farther with the crop camera to get the same size image.

Bad. Perspective changes.

Therefore doing so increases the depth of field for the crop camera.

Or any camera.

Using a 50mm lens on one camera and a 35mm lens on the other camera doesn't seem like a good way to compare depth of field.

Why not? That's the only way to achieve compositionally identical images other than cropping the FF to the size of APS-C.
---
OK, so...

aboss3 wrote in post #10212020 (external link)
I'm considering selling my 7D for 5D MK II, and wanted to know if there's a huge difference in the shallow depth of field when going full-frame? Let's say if we take 50mm f/1.8 lens on the 7D vs 5D MKII, will there be a noticeable difference when shooting portraits?

You are changing formats. The appropriate focal length to use to frame each shot will be different. What point is there in comparing the results of using the correct focal length for one format (e.g. 50 mm on APS-C), with the incorrect focal length for another (e.g. 50 mm on FF).

Establish where you need to be to achieve the perspective you want. Then, select the correct focal length for framing the scene given the format in use*. This will of necessity be different for different formats. Then, select the aperture you need for the DoF you want based on focal length, subject distance, and format. Then arrange shutter speed, ISO, or lighting to obtain correct exposure.

* If you don't have a lens of the correct focal length, you have the option of choosing one shorter and cropping, with some loss of resolution.




  
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May 19, 2010 18:54 |  #8

I believe the general consensus is about 1 - 1/3 stops narrower DoF with same framing and focal length with full frame vs. crop sensor. That means an 80mm lens at f/2 on full frame and a 50mm lens at f/1.2 would give approximately the same photo result, besides the character traits of the given lens at respective apertures/etc.


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SkipD
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May 19, 2010 19:05 |  #9

xarqi wrote in post #10212308 (external link)
What a shambles!

With all the discussion of this in the forum, I find it amazing how many incorrect answers still pop up concerning depth of field.

xarqi wrote in post #10212308 (external link)
* If you don't have a lens of the correct focal length, you have the option of choosing one shorter and cropping, with some loss of resolution.

Additional: If the same focal length (and aperture) are used on two format cameras and the image from the larger format camera is cropped to match the image from the smaller format camera, then the resulting depth of field for both printed images (printed at the same size) will be identical.


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diabolus
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May 19, 2010 19:47 |  #10

SkipD wrote in post #10212278 (external link)
You must realize that the suggestions above to change the camera position when using the same focal length on two different format cameras will NOT produce the same image in both cameras. That's because changing the camera-to-subject distance will change the perspective and that could easily make a huge difference in the composition of the images.

The only depth-of-field comparison that makes any logical sense when using two different format cameras is to use focal lengths on both cameras that provide the same field (angle) of view and use both cameras from precisely the same position.

If you use a depth of field calculator such as DOFMaster (external link), you must enter several variables. One is the "circle of confusion" which is entered in DOFMaster by choosing the camera format. You also enter the focal length, aperture used, and distance to the sharply focused point (usually the primary subject of an image). Make sure that you use focal lengths for both cameras that will provide the same field (angle) of view such as 50mm on the APS-C format and 80mm on the so-called "full-frame" format.

I ran an example through DOFMaster. Assume that the subject (sharply focused plane) is at 20 feet from both cameras. Use 50mm on the 7D, set at f/8. Use 80mm on the 5D, also set at f/8. The images from both cameras will be framed the same.

The results are:

7D - depth of field is 17 feet (distance from camera from 14.6 to 31.6 feet)
5D - depth of field is 9.5 feet (distance from camera from 16.3 to 25.8 feet)

For those folks needing to understand perspective, please read our "sticky" (now found in the General Photography Talk forum) tutorial titled Perspective Control in Images - Focal Length or Distance?.

You are correct. Thanks for re-posting that link. It's been a while since I've read that thread.


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May 19, 2010 19:51 |  #11

aboss3 wrote in post #10212020 (external link)
will there be a noticeable difference when shooting portraits?

Yes.


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aboss3
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May 19, 2010 20:27 |  #12
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Thanks. I should have taken the distance to subject into consideration and totally messed up. Now things are clear :)) I was just confused about the FF sensor, which is 3x of the crop size, and thought that would also change the perspective.


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sportsshooter50
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May 19, 2010 21:29 |  #13

For what it's worth, here's a paragraph from the Canon CMOS whitepaper regarding depth of field for crop and full-frame sensors.

When a lens designed to image on a full-frame field is used with a smaller
sensor, changes occur. If a person switched from full-frame to APS-C while using
the same lens, he or she would have to back up (if possible) to maintain the size of
the subject in the finder, or, one could say, the crop. With a greater subject-camera
distance, depth-of-field would now increase if the aperture remains constant. Background blur and subject-background relief would be reduced.




  
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aboss3
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May 19, 2010 21:51 |  #14
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sportsshooter50 wrote in post #10213057 (external link)
For what it's worth, here's a paragraph from the Canon CMOS whitepaper regarding depth of field for crop and full-frame sensors.

When a lens designed to image on a full-frame field is used with a smaller
sensor, changes occur. If a person switched from full-frame to APS-C while using
the same lens, he or she would have to back up (if possible) to maintain the size of
the subject in the finder, or, one could say, the crop. With a greater subject-camera
distance, depth-of-field would now increase if the aperture remains constant. Background blur and subject-background relief would be reduced.

That explains it :)


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SkipD
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May 19, 2010 22:17 |  #15

sportsshooter50 wrote in post #10213057 (external link)
For what it's worth, here's a paragraph from the Canon CMOS whitepaper regarding depth of field for crop and full-frame sensors.

When a lens designed to image on a full-frame field is used with a smaller
sensor, changes occur. If a person switched from full-frame to APS-C while using
the same lens, he or she would have to back up (if possible) to maintain the size of
the subject in the finder, or, one could say, the crop. With a greater subject-camera
distance, depth-of-field would now increase if the aperture remains constant. Background blur and subject-background relief would be reduced.

While those statements are true, there's nobody in their right mind (and with the correct knowledge about photography) who would choose to use the same focal length on two different format camera bodies to make what should be the same image.

Whoever wrote that piece did not mention the fact that by changing the camera's position the perspective of the image is altered. The fact is that the composition could be significantly altered by changing the camera's position even though the framing of the "primary subject" of the photo stays the same.


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5D Mark II vs 7D depth of field
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