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Thread started 10 Feb 2013 (Sunday) 16:55
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Why does FF yield shallower DOF?

 
gjl711
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Feb 11, 2013 08:32 |  #31

JohnB57 wrote in post #15597591 (external link)
Also = different picture.

The framing will be different if you assume you are using the whole frame. In the OPs question they specifically listed out that the FF image was cropped to match a crop camera. Thus, in the context of the OPs question, you get identical framing as well.


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gjl711
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Feb 11, 2013 08:36 |  #32

JeffreyG wrote in post #15597614 (external link)
But then is isn't the same picture. Who uses cameras this way?...

Bird and wildlife photographers. Imagine I am taking a picture of a bird on a branch. In my crop camera the bird may fill the frame. In the FF camera I get a little bird and a lot of branch so I crop the image to match the crop camera thus the bird fills the frame.

I agree that though the OPs question is not of much interest because in essance what the OP has done is transformed the FF camera into a crop camera. So, same lens, same distance, same aperture, same sensor size will yield the same DOF.

Now the other debate about using the full FF sensor is way more interesting but that is not what was asked.


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gjl711
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Feb 11, 2013 08:38 |  #33

n1as wrote in post #15595460 (external link)
If you shoot with the same lens on both cameras (same scene, same shooting position, same f/stop) and then crop the FF image to equal the FoV of the 1.6 crop-factor sensor will you have the same DOF?

francis_a wrote in post #15597611 (external link)
If the crop is done in post, wouldn't the DOF be exactly the same?

However, if the framing of the FF is done to match the crop, then the FF has to zoom in which increases the FL, which then decreases DOF.

It would, but then something would have to change, focal length, distance, something to frame them the same. OP doesn't want that.


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Feb 11, 2013 08:43 |  #34

gjl711 wrote in post #15597646 (external link)
It would, but then something would have to change, focal length, distance, something to frame them the same. OP doesn't want that.

Whatever happened to the OP's first paragraph then? He did specifically ask about the DOF differences in context of different focal lengths. This is in fact how people normally use cameras with the exception of the very long tele situations where they may become focal length limited.

And the OP' second paragraph addressed this alternate scenario.

I dunno why you keep insisting the OP only wants to know about the less common focal length restricted scenario. His first paragraph directly asked about the much more common use of different formats while framing the same.


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Feb 11, 2013 08:47 |  #35

francis_a wrote in post #15597611 (external link)
If the crop is done in post, wouldn't the DOF be exactly the same? YES

However, if the framing of the FF is done to match the crop, then the FF has to zoom in which increases the FL, which then decreases DOF. YES

Yes!


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Feb 11, 2013 08:48 |  #36

i guess it does, my bad. Argue away. 80 pages here we come. :):)


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Feb 11, 2013 09:00 |  #37

50mm @ f1.2 on a 7D at 3 ft away = .05ft DOF
50mm @ f1.2 on a 5D at 3 ft away = .07ft DOF

So close it's the same. So go take a photo with a FF camera, the photo will have a certain amount of DOF. Now take that photo on the computer and crop it, the DOF hasn't changed, all you have done is crop the image. With a crop camera you're basically cropping on site when the picture is taken.

Just think of it that way and it'll all make sense. If Perspective, FOV, distance, pixel density etc are mentioned then we're changing the subject like others have already mentioned.


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Feb 11, 2013 09:50 |  #38

I'm going back to the original post, and I will eschew all the scenario variations.

n1as wrote in post #15595460 (external link)
To get the same field of view, the crop-sensor camera needs to shoot with a shorter lens. The shorter lens yield wider DOF. Is that why the crop-sensor gives more DOF?

If you changed the focal length to achieve the same field of view, that means you maintained the same distance and I'll presume maintained the same aperture. In that scenario, the reason you gained depth of field is because the aperture of the shorter lens (which is physically proportional to the focal length) is physically smaller than the aperture of the longer lens and the sensor is optically closer to the optical focus node of the lens.

Light isn't affected by the size of the sensor, but it is affected by the physical size of the aperture and the distance from the optical focus node of the lens, and you changed both of those factors. That gives you more depth of field.

If you shoot with the same lens on both cameras (same scene, same shooting position, same f/stop) and then crop the FF image to equal the FoV of the 1.6 crop-factor sensor will you have the same DOF?

This introduces another factor that someone above alluded to. Depth of field is not fixed by the shooting circumstances, but is also affected by the degree of enlargement to the final display size.

We saw this all the time working with film--we'd make a contact print that look pleasingly sharp, but when we enlarged the image--dang, it was out of focus. Of course, you can see it on your monitor as well.

This introduces a new term: Depth of focus. Depth of focus is not to be confused with depth of field. Depth of focus occurs at the sensor. Without going into detail (you can Google "depth of focus"), depth of focus is locked in upon capture. It represents, if you will, what depth of field would be if you did not enlarge the image at all from the sensor dimensions, but viewed it at normal reading distance just as it was projected by the lens.

Once you begin enlarging the image, the resulting depth of field will be less than the depth of focus, decreasing directly according to the degree of enlargement. That includes the increased enlargement resulting from cropping, whether "cropped" by the fact of a smaller sensor or cropped in post-processing.




  
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Feb 11, 2013 09:59 |  #39

gjl711 wrote in post #15597579 (external link)
You guys are totally missing the question. Same lens, same position, same f/stop, same crop = same DOF.

That was not the OP's question. The OP's question was: Different lens, different crop, same position=More Depth of Field.




  
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learncanon
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Feb 11, 2013 10:08 as a reply to  @ RDKirk's post |  #40

Shallower because you need to move in 1.6 times closer to the subject.

It does not yield shallower DOF if you are standing at same distance to a crop camera.




  
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Feb 11, 2013 10:16 |  #41

Why can't this site pop up an automatic popcorn dispenser when it detects some of these "magical" keywords in a new thread :D


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Feb 11, 2013 10:30 |  #42

Canon_Lover wrote in post #15595535 (external link)
There are plenty of articles and threads already explaining this. Please do a search.

Such a topic will spawn an 80 page thread again... :lol::lol:

3/80 and counting!:lol:


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Feb 11, 2013 10:45 |  #43

n1as wrote in post #15595759 (external link)
Please don't assume I didn't search. I did but found no quick answers.

Fortunately, the 80 pages will be nicely contained in this one thread where people who are uninterested in the topic can safely step around it.

hopefully not, if you searched and did not understand, maybe some elementary math is in order...


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Feb 11, 2013 10:50 |  #44

learncanon wrote in post #15597921 (external link)
Shallower because you need to move in 1.6 times closer to the subject.

It does not yield shallower DOF if you are standing at same distance to a crop camera.

I think you may have a bit of reading to do...




  
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Feb 11, 2013 11:27 |  #45

msowsun wrote in post #15597566 (external link)
A Point and Shoot camera is a Crop camera.

I don't know about the above statement......... so that means the 10D, 20D, 50D, 60D, 7D are point and shoots? Come on.... Lest not forget the APS-H 1D series bodies are crop as well, so I guess we can throw them into the point and shoot group too?


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