Longshadow Loc: Audubon, PA, United States

But one must know the details.....

selmslie Loc: Fernandina Beach, FL, USA

There is but it's based on the assumption that you don't crop the result during editing and that you are going to view it from a standard distance with normal eyesight.

Rather than drive yourself nuts with the math, just play with this depth of field calculator from Cambridge in Colour. Be sure to click on show advanced to see most of the contributing factors.

What they leave out is the effect of cropping on your computer (which changes the size of the circle of confusion) because there you can even change the aspect ratio.

It's all hardly worth the trouble to dwell on it.

Longshadow Loc: Audubon, PA, United States

Exactly.
Anyone take a tape measure with them?

Tomfl101 Loc: Mount Airy, MD

Here’s all you need to know:
The greater the distance from camera to subject, the greater the depth of field.
At any given focal length or aperture a crop sensor camera will need to be moved farther away from an object to maintain the same image size from that of a full frame camera. That increase in distance will add DOF and will produce a sharper background with less bokeh. This is why cell phones have such massive DOF. Their sensors are tiny.

Longshadow Loc: Audubon, PA, United States

Works for me.

tcthome Loc: NJ

even after post processing!

burkphoto Loc: High Point, NC

ƒ/stop is a fraction. It is the focal length of the lens divided by a number.

For a 50mm lens, 50/4 = 12.5mm diameter, the ACTUAL APERTURE for f/4 on a 50mm lens.

For a 100mm lens, 100/4 = 25mm diameter, the ACTUAL APERTURE for f/4 on a 100mm lens.

The practical reason we use f/stops and not actual diameter is to equate the amount of light passing through the lens. f/4 on a 50mm and a 100mm lens is roughly the same. There are minor differences due to the number of glass elements, coatings, manufacturing tolerances, etc., but for most purposes, f/4 is f/4 is f/4, unless you are trying to match multiple cameras together. In that case, you need those very expensive ciné lenses calibrated in T/stops, where T is the f/stop adjusted for actual light transmission.

Longshadow Loc: Audubon, PA, United States

Again...
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.

selmslie Loc: Fernandina Beach, FL, USA

That’s the only approach that makes sense.

Sinewsworn Loc: Port Orchard, WA

Thanx for presenting this interesting info. I do not do calculations; I trip the trigger! Modern cameras do so much and post-production options are so good allowing us to concentrate on focus and composition thus helping us to improve our images.

M1911 Loc: DFW Metromess

Aw hell, just use the F16 rule.

MJPerini

DOF is a property of the lens, not the sensor. For any given lens the DOF tends to increase with smaller f/stops........ Until you get to a pinhole where everything is sharp (except for the fact that it is degraded by diffraction.

Where things get confusing is that the Idea that crop sensors have more depth of field --everyone leaves off FOR EQUIVALENT ANGLES OF VIEW. If we take a 50mm lens on FF and a 25mm lens on M4/3 they will have the same angle of view and the DOF of the M4/3 will be greater NOT because of the sensor size but because 25mm is shorter than 50 mm.
Think about it this way. Crop sensors are called that because they are cropped relative to FF. It is probably not the best term. But if you had a FF camera that allowed different crops and you put the camera on a tripod and took shots at FF, APS-c, and M4/3 with the 50mm lens , each smaller crop would show a decrease in angular view but the DOF for all 3 would be identical.
In common use we think of wide angle, Normal and telephoto lenses. In order to achieve that we all know that the Actual focal lengths will be comparatively shorter for each type on M4/3 than FF SO, for equivalent fields of view m4/3 will have more DOF that the Wide , normal or Tele in the FF set.

Similarly, the difference between F'stop and Aperture is that One is a ratio, the other a physical "APERTURE"
As a simplification for a 100 mm lens to be F2, it must have a clear Aperture (opening) of 50mm
For a 200 mm lens to be f/2 it must have a clear aperture of 100 mm and for a 50mm lens to be F2 it must have a clear aperture of 25mm. All 3 lenses are f/2 all have different physical apertures

This also explains why longer lenses have less DOF than Shorter lenses. Remember the pinhole unlimited DOF but degraded by diffraction (caused by light scattering when it encounters an edge.)
So DOF increases inversely with the size of the physical aperture. If I have 2 lenses , a 50/2 and a 100/2 the 50 will have more DOF BECAUSE the physical Aperture is smaller ..... approaching the pinhole.
Similarly all lenses have diffraction, we don't notice it with fast lenses Because they have a big Aperture and 99% of the image forming light comes through the big hole and 1% brushes the edges. In a Pinhole, the hole is so small that the proportion of edges to clear aperture is much greater -- I'm guessing 50/50, so diffraction is a big problem.
And Lastly this also explains why crop sensor cameras see diffraction effects sooner than larger formats....
BECAUSE FOR ANY GIVEN F/STOP THE PHYSICAL SIZE OF THE APERTURE IS SMALLER (CLOSER TO THE PINHOLE)

In optics a 'perfect lens' is often described as "Diffraction Limited" meaning otherwise perfect but diffraction is a physical reality for all lenses

F/stops are RATIOS (F.L./Aperture), Apertures are physical holes.
DOF is a property of lenses not sensors
Remember Equivalent Fields of view

I hope this helps a bit....

User ID

Its perfickly OK to know useless detail.

Its not very OK to post blah-blah 5 screen lengths deep, just the show off how much useless detail one thinks they know. Extra demerits for gratuitous charts and graphs.

And its waaaaaay short of OK to post essay length phony expert blah-blah-blah showing the formidable depth of ones cluelessness ... Extra demerits for folding ones resume into the essay. (But theres no law against it.)

User ID

Okay as "all you need to know" type of advice, but all that you reeeeally need to know is that *knowing nothing* is waaaay more betterer !

Lester_Macro Loc: New York

There's a lot of contorted semi-mis-information here.

The optical calculations for DOF are a function of MAGNIFICATION, M, and aperture, NOT focal length or sensor size. PERIOD! Make the SAME photos (same field-of-view) with FF and M4/3. Get the same FOV by either moving your ass or change focal length, it doesn't matter. But to get , say, a 3ft. wide subject on a FF camera, you will need LESS magnification than the same 3ft-wide subject on a M4/3 sensor. Less magnification leads to MORE DOF. It turns out it's about two stops more DOF with M4/3, and one stop more with APS-C, for the same FOV and same f/stop.

This science is well know among macro photographers, where DOF is a never-ending battle. The above is one reason why Olympus M4/3 systems have become popular with the macro crowd. To fill the frame with the same bug, you get much more DOF with the M4/3 system than with a FF, because the M4/3 system only need 1/2 the magnification. DOF decrease approximately as the inverse of the square of magnification; that's a big deal. Macro photographers know that focal length has no bearing on DOF, but it does effect working distance.

Lester Lefkowitz www.MacroPhotographer.net