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"You have a 4mm lens at f/2. To get the same depth of field you'd need a 50mm lens at f/25, not f/512." Humorously years back I had authored a giant depth of f

"You have a 4mm lens at f/2. To get the same depth of field you'd need a 50mm lens at f/25, not f/512." Humorously years back I had authored a giant depth of field essay with online calculators specifically because so many people just couldn't understand why their iPhone couldn't get bokeh. Yes, f/512 would be the impossible equivalent. This is easily calculated. Regardless, the lens Apple uses for macro mode has a 1.54mm focal length. The 4mm example was just demonstrating how fundamentally small cameras win on depth of field, at least if you want maximal depth of field. Conversely they lose when you want to limit depth of field, which is why we have computational bokeh. "Macro lenses are typically 24mm or so." The smallest from most makers is 35mm, but the majority are 50mm+. This conversation has turned weird. As someone who has had many SLRs, and many lenses, and has taken thousands of macro photos, I know that in the real world macro photography is a massive pain. That DoF is by far the number one obstacle (which is why focus stacking is simply necessary, often with ten or more varied focuses). Physics benefits small camera systems for that specific scenario.

sudosysgen 5y ago
That's just not how lenses work, fundamentally. Bokeh is determined by two things, and two things only - the diameter of the aperture and the distance to the object. That's it. Also yes, the wide angle of the iPhone 13 is much smaller. Just stop down even further then. Cheap macro lenses in 2021 are typically around 24mm. I'm talking about the Mitakons and the Laowas of the world. Focus stacking is needed when you're trying to take very high detail pictures with 60, 70, 90mm lenses on high resolution sensors. You don't need anywhere near as much to take an image with the same magnification as a 13mm equiv. 2cm away.
- defaultname 5y ago
  "That's just not how lenses work, fundamentally." Go to the wikipedia page on depth of field and see how it is calculated. "Cheap macro lenses in 2021 are typically around 24mm" You claimed they were the norm. Now it's that they simply exist. "Focus stacking is needed" Focus stacking is needed when the depth of field is so small that the resulting photo would be unpleasant. This is the case for almost all macro photographs shot on SLRs. It's interesting that someone else claimed this is a fixed issue and posted a photo that looks like it was taken with one of those terrible lens adapter kits. If that is one's standard for "fixed", then sure, but most of us have higher standards.
  - foldr 5y ago
    I think you are right if you hold constant the CoC. In that case the DoF is proportional to the f number but inversely proportional to the square of the focal length (http://graphics.stanford.edu/courses/cs178/applets/dof.html http://graphics.stanford.edu/courses/cs178/applets/dof.html). However, for a smaller format, we arguably ought to reduce the CoC proportionally. And I think that reduction will end up canceling out one factor of f, bringing us back to the ratio of the focal length to the f stop (i.e. the absolute diameter of the aperture).
    - defaultname 5y ago
      The focal length input is squared, but the CoC impact is linear. The iPhone has a small CoC compared to SLRs, but its input on the calculation is undersized relative to focal length. The iPhone is widely assumed to have a CoC of 0.004mm (this actually increases on the most recent iPhone, though it's tough to get precise numbers). A Nikon D5000 (going with an equivalent resolution -- larger pixels -- on an ASP-C camera) has a CoC of 0.020. So let's calculate hyperfocal distance of the two systems for the same effective focal length (but obviously very different real focal lengths)- iPhone 12 telephoto lens - 65mm (7.5mm real) equivalent, f2.2. Nikon D5000 equivalent lens - 65mm (43mm real) equivalent, f2.2. For the iPhone, the HF is 6.4m. For the Nikon, it is 54.3m. For those who don't know, hyperfocus is the point where everything from 1/2 of that distance to infinity is in focus if you set the focus to that magical point. It's a proxy for the other depth of field calculations, and is the simplest to demonstrate. Anyone who owns an iPhone w a "telephoto" and an ASP-C SLR w/ a 50mm lens needs to try to replicate bokeh at various distances without the computational bokeh. Focus on a subject at 1m, 2m, 4m, etc at the same aperture. Close down the aperture on the SLR even.
      - foldr 5y ago
        Holding constant the target resolution, you need a smaller CoC in proportion to the difference in focal lengths (assuming the viewing angle is also held constant). That removes one of the factors of f. I think it makes sense to assume the same target resolution for the iPhone and the DSLR, even though this isn’t true in practice. The DSLR user is obviously free to downsample their photo to a lower resolution and thereby (in a rather uninteresting way) gain more depth of field. We shouldn’t be giving the iPhone extra DoF points just because it happens to have a lower resolution. So we are not talking about any empirically derived value for the iPhone’s CoC. The CoC here is a value derived for each format from an arbitrarily chosen target resolution.
- deleted 5y ago
  [deleted]
- sib 5y ago
  If you are going to try to get persnickety, that's not "bokeh" at all. It's depth of field. Bokeh is the quality of rendering of out-of-focus highlights.

sudosysgen 5y ago

That's just not how lenses work, fundamentally. Bokeh is determined by two things, and two things only - the diameter of the aperture and the distance to the object. That's it. Also yes, the wide angle of the iPhone 13 is much smaller. Just stop down even further then. Cheap macro lenses in 2021 are typically around 24mm. I'm talking about the Mitakons and the Laowas of the world. Focus stacking is needed when you're trying to take very high detail pictures with 60, 70, 90mm lenses on high resolution sensors. You don't need anywhere near as much to take an image with the same magnification as a 13mm equiv. 2cm away.

defaultname 5y ago
"That's just not how lenses work, fundamentally." Go to the wikipedia page on depth of field and see how it is calculated. "Cheap macro lenses in 2021 are typically around 24mm" You claimed they were the norm. Now it's that they simply exist. "Focus stacking is needed" Focus stacking is needed when the depth of field is so small that the resulting photo would be unpleasant. This is the case for almost all macro photographs shot on SLRs. It's interesting that someone else claimed this is a fixed issue and posted a photo that looks like it was taken with one of those terrible lens adapter kits. If that is one's standard for "fixed", then sure, but most of us have higher standards.
- foldr 5y ago
  I think you are right if you hold constant the CoC. In that case the DoF is proportional to the f number but inversely proportional to the square of the focal length (http://graphics.stanford.edu/courses/cs178/applets/dof.html http://graphics.stanford.edu/courses/cs178/applets/dof.html). However, for a smaller format, we arguably ought to reduce the CoC proportionally. And I think that reduction will end up canceling out one factor of f, bringing us back to the ratio of the focal length to the f stop (i.e. the absolute diameter of the aperture).
  - defaultname 5y ago
    The focal length input is squared, but the CoC impact is linear. The iPhone has a small CoC compared to SLRs, but its input on the calculation is undersized relative to focal length. The iPhone is widely assumed to have a CoC of 0.004mm (this actually increases on the most recent iPhone, though it's tough to get precise numbers). A Nikon D5000 (going with an equivalent resolution -- larger pixels -- on an ASP-C camera) has a CoC of 0.020. So let's calculate hyperfocal distance of the two systems for the same effective focal length (but obviously very different real focal lengths)- iPhone 12 telephoto lens - 65mm (7.5mm real) equivalent, f2.2. Nikon D5000 equivalent lens - 65mm (43mm real) equivalent, f2.2. For the iPhone, the HF is 6.4m. For the Nikon, it is 54.3m. For those who don't know, hyperfocus is the point where everything from 1/2 of that distance to infinity is in focus if you set the focus to that magical point. It's a proxy for the other depth of field calculations, and is the simplest to demonstrate. Anyone who owns an iPhone w a "telephoto" and an ASP-C SLR w/ a 50mm lens needs to try to replicate bokeh at various distances without the computational bokeh. Focus on a subject at 1m, 2m, 4m, etc at the same aperture. Close down the aperture on the SLR even.
    - foldr 5y ago
      Holding constant the target resolution, you need a smaller CoC in proportion to the difference in focal lengths (assuming the viewing angle is also held constant). That removes one of the factors of f. I think it makes sense to assume the same target resolution for the iPhone and the DSLR, even though this isn’t true in practice. The DSLR user is obviously free to downsample their photo to a lower resolution and thereby (in a rather uninteresting way) gain more depth of field. We shouldn’t be giving the iPhone extra DoF points just because it happens to have a lower resolution. So we are not talking about any empirically derived value for the iPhone’s CoC. The CoC here is a value derived for each format from an arbitrarily chosen target resolution.
deleted 5y ago
[deleted]
sib 5y ago
If you are going to try to get persnickety, that's not "bokeh" at all. It's depth of field. Bokeh is the quality of rendering of out-of-focus highlights.