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02-05-2015, 05:44 PM   #1
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APS-C vs FF Bokeh?

Iíve often seen it said that full frame provides better bokeh (or depth of field) than APS-C. Iím not sure what this means and am hoping to clarify it with this question:

Assuming you the new Pentax full frame camera has the same pixel pitch as the K-3, if you mounted the DA* 55 f/1.4 on both (this lens is full frame compatible) and set it to f/1.4 on both and took the same picture, would the resulting image be the same between the two, just that the image from the K-3 would be the center area of the image from the Pentax full frame camera?

02-05-2015, 05:48 PM - 1 Like   #2
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QuoteOriginally posted by Newtophotos Quote
Iíve often seen it said that full frame provides better bokeh (or depth of field) than APS-C. Iím not sure what this means and am hoping to clarify it with this question:

Assuming you the new Pentax full frame camera has the same pixel pitch as the K-3, if you mounted the DA* 55 f/1.4 on both (this lens is full frame compatible) and set it to f/1.4 on both and took the same picture, would the resulting image be the same between the two, just that the image from the K-3 would be the center area of the image from the Pentax full frame camera?
Ti take the same image, you'd have to back up with the K-3, and that would create more Depth of Field. That's true with any lens. The closer you are, the smoother your out of focus areas will be. You can get smooth out of focus areas with a point and shoot, if your subject is 3 feet away, and your background is 40 feet away.
02-05-2015, 05:52 PM   #3
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QuoteOriginally posted by Newtophotos Quote
Iíve often seen it said that full frame provides better bokeh (or depth of field) than APS-C. Iím not sure what this means and am hoping to clarify it with this question:

Assuming you the new Pentax full frame camera has the same pixel pitch as the K-3, if you mounted the DA* 55 f/1.4 on both (this lens is full frame compatible) and set it to f/1.4 on both and took the same picture, would the resulting image be the same between the two, just that the image from the K-3 would be the center area of the image from the Pentax full frame camera?
Some one can correct me. My understanding is that in the same distance, DOF is equal or slightly narrow in APS-C comparing to FF (you can try this using DOF calculator). So if you take the same object at the same distance using the distance, the bokeh should be equal or at least not worse for APS-C comparing to FF.

It will be a different story when you use the same lens and move backward for APS-C to get the same picture as now APS-C camera is further away from the object and DOF increased.
02-05-2015, 06:03 PM - 1 Like   #4
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It's already been said, but I'll re-phrashe it slightly. Depth of field is a function of aperture, focal length, and distance to the subject. The first two do not change when moving between APS-C and 36x24

What does change is angle of view, so on the FF camera the lens gives a wider field of view. To frame the subject the same as with APS-C you have to get closer, which puts the background relatively further away from the focal plane, making it more blurred.

02-05-2015, 06:08 PM   #5
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Bokeh is actually completely determined by the lens design (focal length, aperture blades, elements) and distance to focus and to background (objects that turn to bokeh).
You will get the most bokeh at minimum focus distance and widest aperture. This is why macro is so challenging - at extremely close MFD, the DoF is incredibly shallow, and bokeh is "huge"!

On to differences between FF and APSC. The bokeh is actually exactly the same, if you use the same lens and focus setting. It will be different if you use different lenses (different focal length, but equivalent FoV) or if you move the camera (further or closer, to get the same framing). But if everything is the same, the bokeh will be the same - except that on crop sensor part of the edges will be cropped. This gives the illusion that the magnification is higher, so bokeh balls can appear to cover more of the frame.

One more thing about calculated DoF.. in my experience, the old zone focusing and DoF scales on film-era lenses no longer apply in digital cameras. This is mostly because the resolution of digital sensors is very high, and also our expectations of detail and sharpness is very high these days. DoF was the area that is "adequately" sharp to be considered "in focus". What used to be adequate in the past, on a different medium (film), is no longer necessarily adequate with our standards now, with the new medium (digital sensors with high pixel density). This is why those DoF calculations have to be taken with much reserve. Try them out sometime, see if they satisfy you.
02-05-2015, 06:15 PM   #6
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QuoteOriginally posted by Newtophotos Quote
Assuming you the new Pentax full frame camera has the same pixel pitch as the K-3, if you mounted the DA* 55 f/1.4 on both (this lens is full frame compatible) and set it to f/1.4 on both and took the same picture, would the resulting image be the same between the two, just that the image from the K-3 would be the center area of the image from the Pentax full frame camera?
Affirmative [I just learned that PF won't take a simple "Yes" reply. We have to write at least 5 characters.]
02-05-2015, 06:19 PM - 1 Like   #7
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Oh, I get it. You were confused by the "equivalists" who claim things like bokeh is better on FF, DoF is more shallow on FF, etc. I think it is best to just ignore all that, as it is based on convoluted comparisons. Basically, they want you to take a photo with FF camera, then go out of your way to try to imitate that photo with a crop sensor camera, to get the exact same FoV, DoF, and bokeh. And since it is impossible to get the same focal length, FoV, DoF, and bokeh at the same time, they claim APSC failed - it has to sacrifice some of those elements, like DoF, to achieve a "similar" photo. But this is a skewed comparison. Using less or more of the sensor, using a bigger or smaller film, will not change the rendering of the image. It will only change how much of the image area is recorded. Trying to then imitate a theoretical DoF and maintain a FoV, upsampling the photo and so on will always skew the results in favour of the "native" format

FF does not give better bokeh or shallower DoF. It just gives a bigger frame. If you try to force a camera with a smaller frame to get the same FoV and DoF (at the same time), you will have a hard time, and possibly get sub-par results. But nobody actually takes photos in that manner, first looking at DoF and bokeh magnification. Theory and practice.

Last edited by Na Horuk; 02-05-2015 at 06:27 PM.
02-05-2015, 07:08 PM   #8
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Misleading title. The size of a sensor has little to do with how a lens renders its out of focus areas (bokeh)

02-05-2015, 07:38 PM - 1 Like   #9
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I give a bit of a slant to the discussion.

FF does affect bokeh or the overall impression of the bokeh, because if shows up portions of the image circle that was cropped off on aps-c.
Can be a good thing, can be a bad thing.
Other aspects, as discussed by others, FF does not necesarily mean better bokeh more does it really affect DOF as a term in itself.


CZJ Biotar 75/1.5, the swirl effect (for the good and bad of it) won't be as apparent on aps-c.




Pentax K85/1.8, I did not even know that it had a bit of a swirl until I tried it on FF.

02-05-2015, 08:00 PM   #10
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An APS-C lens will show you all of its image circle too.
02-05-2015, 08:15 PM   #11
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QuoteOriginally posted by Sandy Hancock Quote
It's already been said, but I'll re-phrashe it slightly. Depth of field is a function of aperture, focal length, and distance to the subject. The first two do not change when moving between APS-C and 36x24

What does change is angle of view, so on the FF camera the lens gives a wider field of view. To frame the subject the same as with APS-C you have to get closer, which puts the background relatively further away from the focal plane, making it more blurred.
YES!

And to get a similar field of view of a particular subject/scene one would need to physically move OUT and AWAY from the subject (to capture the same framing). With a FF you need to move TOWARDS and IN to the subject for that same framing. Say for example if I am using my 31mm on a crop I need to stand in X spot to capture said scene. If I want that same scene with a FF I need to stand in Y spot, which Y would be physically closer. This in turn allows for the appearance of more DOF control on a FF.

If I am shooting a picture of a person with a FF and I am 3 feet away I need to stop down to get my subject in focus. I might need to go to f2.8 or so...whereas with a crop because I am farther away (with the same scene) I might need to use f1.8 to mirror the desired DOF.

The lens doesn't change it's stripes. It doesn't transmit more light or less light. But the dynamic of how the lens is used changes.

And to further complicate things.... lets say you had a 31mm on a crop and a 50mm on a FF which are very loosely similar FOV when standing in the same physical proximity to the subject.

The Field of View offered by a FF changes the dynamic of how things are used.
02-05-2015, 08:30 PM   #12
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DoF is unaffected by sensor size.


It's the moving the camera towards and away from the subject that counts.
02-06-2015, 12:59 AM   #13
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QuoteOriginally posted by Newtophotos Quote
Iíve often seen it said that full frame provides better bokeh (or depth of field) than APS-C. Iím not sure what this means and am hoping to clarify it with this question:

Assuming you the new Pentax full frame camera has the same pixel pitch as the K-3, if you mounted the DA* 55 f/1.4 on both (this lens is full frame compatible) and set it to f/1.4 on both and took the same picture, would the resulting image be the same between the two, just that the image from the K-3 would be the center area of the image from the Pentax full frame camera?
yes. That is the case.
02-06-2015, 06:01 AM   #14
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QuoteOriginally posted by normhead Quote
you'd have to back up with the K-3,
True
QuoteOriginally posted by normhead Quote
and that would create more Depth of Field. That's true with any lens. The closer you are, the smoother your out of focus areas will be.
Not necessarily.

Last edited by Oldbayrunner; 02-06-2015 at 06:13 AM.
02-06-2015, 06:48 AM   #15
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QuoteOriginally posted by clackers Quote
DoF is unaffected by sensor size.


It's the moving the camera towards and away from the subject that counts.
From DOFMaster: Circles of Confusion for various size films/sensors :

APS 0.025mm
35mm 0.030mm
645 0.045mm
etc.
So DOF will be affected.
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