Wha'ts all this crop sensor DoF Stuff?
Apr 28, 2024 16:07:29 #
Shooting with 2 formats, Full Frame (FF) and Micro43 (M43) it's OBVIOUS Depth of Fields (DOF) are not equal for the same focal length.
FYI - When I am shooting, i don't do math, I just look thru the viewfinder and I use DoF preview to assess the DOF.
But I was curious if there was a relation, something like the crop factor. But for DoF instead of for field of view. Various u-tube tutorials describe it differently. Some seem to contradict one another. One person said divide by the crop factor but that seems wrong. One of the u-tube videos said with the same framing you get the same field of view. But that's difficult to access because the aspect ratios are different.
So I used my iPhone Application, Simple DoF and did a few comparisons.
Summary below, the columns are:
F-stop focal length focus distance DOF_calculation in feet and inches.
(Apologies to the metric people)
Full Frame
F5.6 50mm 5' 1' 0.13"
M43
F5.6 50mm 5' 0' 6.02"
F5.6 35mm 5' 1' 0.51"
F5.6 25mm 5' 2' 1.48"
So it looks like 35mm gives a pretty close DOF to FF. That's interesting because 35mm is
approximately what you get dividing by the square root of the crop factor.
Let's try it with F4
FF
F4 50mm 5' 0' 8.53"
F8 50mm 5' 1' 5.33"
F16 50mm 5' 3' 0.93"
M43
F4 35mm 5' 0' 8.80"
F8 35mm 5' 1' 5.88"
F16 35mm 5' 3' 2.26"
Again M43 @ 35mm focal length is close to FF @ 50mm focal length.
Let's try it with FF@100mm and M43@71mm
5' Focal distance
FF M43
100mm 71mm
F4 2.05" 2.08"
F8 4.11" 4.16"
F16 8.24" 8.34"
15' Focal Distance
FF M43
100mm 71mm
F4 1' 7.37" 1' 7.34"
F8 3' 3.09" 3' 3.02"
F16 6' 9.01" 6' 8.36"
There is probably some mathematical explanation for this, maybe someone here with optics knowledge can explain it. Or is it just a coincidence?
FYI - When I am shooting, i don't do math, I just look thru the viewfinder and I use DoF preview to assess the DOF.
But I was curious if there was a relation, something like the crop factor. But for DoF instead of for field of view. Various u-tube tutorials describe it differently. Some seem to contradict one another. One person said divide by the crop factor but that seems wrong. One of the u-tube videos said with the same framing you get the same field of view. But that's difficult to access because the aspect ratios are different.
So I used my iPhone Application, Simple DoF and did a few comparisons.
Summary below, the columns are:
F-stop focal length focus distance DOF_calculation in feet and inches.
(Apologies to the metric people)
Full Frame
F5.6 50mm 5' 1' 0.13"
M43
F5.6 50mm 5' 0' 6.02"
F5.6 35mm 5' 1' 0.51"
F5.6 25mm 5' 2' 1.48"
So it looks like 35mm gives a pretty close DOF to FF. That's interesting because 35mm is
approximately what you get dividing by the square root of the crop factor.
Let's try it with F4
FF
F4 50mm 5' 0' 8.53"
F8 50mm 5' 1' 5.33"
F16 50mm 5' 3' 0.93"
M43
F4 35mm 5' 0' 8.80"
F8 35mm 5' 1' 5.88"
F16 35mm 5' 3' 2.26"
Again M43 @ 35mm focal length is close to FF @ 50mm focal length.
Let's try it with FF@100mm and M43@71mm
5' Focal distance
FF M43
100mm 71mm
F4 2.05" 2.08"
F8 4.11" 4.16"
F16 8.24" 8.34"
15' Focal Distance
FF M43
100mm 71mm
F4 1' 7.37" 1' 7.34"
F8 3' 3.09" 3' 3.02"
F16 6' 9.01" 6' 8.36"
There is probably some mathematical explanation for this, maybe someone here with optics knowledge can explain it. Or is it just a coincidence?
Apr 28, 2024 16:21:59 #
"Wha'ts all this crop sensor DoF Stuff?"
It's something some people worry about.
It's something some people worry about.
Apr 28, 2024 16:50:35 #
Apr 28, 2024 16:50:45 #
Ysarex
Loc: St. Louis
From the Wikipedia article on DOF -- it is correct.
"Image sensor size affects DOF in counterintuitive ways. Because the circle of confusion is directly tied to the sensor size, decreasing the size of the sensor while holding focal length and aperture constant will decrease the depth of field (by the crop factor). The resulting image however will have a different field of view. If the focal length is altered to maintain the field of view, the change in focal length will counter the decrease of DOF from the smaller sensor and increase the depth of field (also by the crop factor)." [NOTE: sloppy usage there -- should say f/stop not aperture.]
"Image sensor size affects DOF in counterintuitive ways. Because the circle of confusion is directly tied to the sensor size, decreasing the size of the sensor while holding focal length and aperture constant will decrease the depth of field (by the crop factor). The resulting image however will have a different field of view. If the focal length is altered to maintain the field of view, the change in focal length will counter the decrease of DOF from the smaller sensor and increase the depth of field (also by the crop factor)." [NOTE: sloppy usage there -- should say f/stop not aperture.]
Apr 28, 2024 17:12:25 #
Ysarex wrote:
From the Wikipedia article on DOF -- it is correct... (show quote)
Interesting...
I've always considered ƒ-stop and aperture the same. ƒ-stop simply being a specific value for the aperture.
Apr 28, 2024 17:46:50 #
Ysarex
Loc: St. Louis
Longshadow wrote:
Interesting...
I've always considered ƒ-stop and aperture the same. ƒ-stop simply being a specific value for the aperture.
I've always considered ƒ-stop and aperture the same. ƒ-stop simply being a specific value for the aperture.
F/stop normalizes focal length and aperture diameter for exposure -- f/4 is f/4 is f/4 for all lenses -- same exposure. Different focal length lenses set at the same f/stop will have different diameter apertures and it's the aperture diameter that really determines DOF. However we've set up the DOF formula to be useful for photographers in the field and so the equations in fact use f/stop values.
Apr 28, 2024 18:00:37 #
Ysarex wrote:
F/stop normalizes focal length and aperture diameter for exposure -- f/4 is f/4 is f/4 for all lenses -- same exposure. Different focal length lenses set at the same f/stop will have different diameter apertures and it's the aperture diameter that really determines DOF. However we've set up the DOF formula to be useful for photographers in the field and so the equations in fact use f/stop values.
An ƒ-stop is an ƒ-stop, aperture.
Now when you bring DOF into the picture you are introducing other variables into the "equation", like lens focal length, which affects DOF.
DOF is related to ƒ-stop (variable 1) and lens (variable 2).
Apr 28, 2024 18:07:28 #
JD750 wrote:
Shooting with 2 formats, Full Frame (FF) and Micr... (show quote)
The DOF of the FF divided by the crop factor is correct. The formula is different only for the size of the circle of confusion which is taken to be about 1/1500 the diagonal of the format size.
Apr 28, 2024 19:47:28 #
Ysarex
Loc: St. Louis
Longshadow wrote:
An ƒ-stop is an ƒ-stop, aperture.
An f/stop value is not the aperture. The f/stop value is calculated from the aperture; f/stop = lens focal length / diameter of aperture.
Longshadow wrote:
Now when you bring DOF into the picture you are introducing other variables into the "equation", like lens focal length, which affects DOF.
DOF is related to ƒ-stop (variable 1) and lens (variable 2).
DOF is related to ƒ-stop (variable 1) and lens (variable 2).
And focused distance (variable 3) and size of the sensor/film (variable 4) and size of the final print (variable 5).
Apr 28, 2024 20:29:31 #
Ysarex wrote:
And focused distance (variable 3) and size of the sensor/film (variable 4) and size of the final print (variable 5).
No matter how simple a problem seems at first,
it becomes increasingly more complex upon further investigation.
So the physical opening for an ƒ/11 for one lens is a different physical size for another lens?
Life can get so complicated....
Apr 28, 2024 20:48:50 #
Ysarex
Loc: St. Louis
Longshadow wrote:
No matter how simple a problem seems at first,
it becomes increasingly more complex upon further investigation.
So the physical opening for an ƒ/11 for one lens is a different physical size for another lens?
it becomes increasingly more complex upon further investigation.
So the physical opening for an ƒ/11 for one lens is a different physical size for another lens?
Yes, and it's that physical opening that determines DOF. More specifically (here comes more complicated) it's the diameter of what we call the entrance pupil. In most cases the aperture diameter and entrance pupil diameter are the same or very close, but depending on the lens design there can be enough of a difference to have a small effect.
Longshadow wrote:
Life can get so complicated....
Apr 28, 2024 21:20:45 #
Ysarex wrote:
Yes, and it's that physical opening that determines DOF. More specifically (here comes more complicated) it's the diameter of what we call the entrance pupil. In most cases the aperture diameter and entrance pupil diameter are the same or very close, but depending on the lens design there can be enough of a difference to have a small effect.
So glad I don't worry about all that stuff.!.!
I just use a large, small, or medium aperture for the effect I want, primarily on one lens mostly.
Small, large, or medium DOF, for whatever the lens does.
No sensor size worries either.
I just use the camera.
Apr 28, 2024 23:56:42 #
Longshadow wrote:
yes...So the physical opening for an ƒ/11 for one lens is a different physical size for another lens?
F-stop = focal length / aperture_diameter
It’s a normalized value. F5.6 on a 100mm lens at 1/500 sec will give you the same exposure as F5.6 on a 50mm lens at 1/500 sec.
Apr 29, 2024 00:18:34 #
Longshadow wrote:
Interesting...
I've always considered ƒ-stop and aperture the same. ƒ-stop simply being a specific value for the aperture.
I've always considered ƒ-stop and aperture the same. ƒ-stop simply being a specific value for the aperture.
Specific is waaaaaaaay moe betterer.
"Aperture" taken literally is a dimension (in linear units like mm, cm) that is useless info to photographers. Its a physical diameter of a hole, useless for setting exposures.
"Aperture blades" by shape and quantity is useful info to some (geekish) photographers, although the more accurate term would be "iris blades". Nine curved iris blades is the minimum for bokeh cultists.
Apr 29, 2024 00:40:20 #
If you have a good working feel for DoF with FF cameras at various f/stops then use the "crop factor" to translate that working feel to the APSC and m4/3 cameras.
Two simple examples based on same field of view (*NOT* same focal length !!!!):
m4/3 at f/4 is same DoF as FF at f/8 (m4/3 "crop factor" being 2X).
APSC at f/4 is same DoF as FF at f/6 (by the 1.5X factor). Acoarst you would set f/5.6 cuz common sense.
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The above also works for large formats. The "grow factor" for 6x7 or 6x9 rollfilm is *very* approximately 0.5X. So f/16 on your baby Graphic, Pentax 6x7, etc is the same DoF as f/8 on your D850, Sony a7xx, etc or same as f/4 on your OMD or Lumix. (ALL same FoV.)
EVERYTHING in photography is always approximate. Just dont tell Selmsie, Ysarex and the rest of the geeks. We dont need to rain on their parade !
Two simple examples based on same field of view (*NOT* same focal length !!!!):
m4/3 at f/4 is same DoF as FF at f/8 (m4/3 "crop factor" being 2X).
APSC at f/4 is same DoF as FF at f/6 (by the 1.5X factor). Acoarst you would set f/5.6 cuz common sense.
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The above also works for large formats. The "grow factor" for 6x7 or 6x9 rollfilm is *very* approximately 0.5X. So f/16 on your baby Graphic, Pentax 6x7, etc is the same DoF as f/8 on your D850, Sony a7xx, etc or same as f/4 on your OMD or Lumix. (ALL same FoV.)
EVERYTHING in photography is always approximate. Just dont tell Selmsie, Ysarex and the rest of the geeks. We dont need to rain on their parade !
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