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.
24mm is a normal focal length for entry level macro lenses nowadays, yes. They don't just exist, they are very common in the entry level market. If you want to get those kinds of macro shots that's what you'll get.
If your goal for macro photography is to take a picture that is reasonably sharp at 12MP 2cm away with a magnification of less than 2, then yes, getting acceptable depth of field is a solved problem. Set your wide angle macro lens to F/22 and there you go.
If you have higher standards, then the problem is not fixed on DSLRs. But the iPhone doesn't do it either.
If you don't understand why using the CoC criteria for depth of field is incorrect on two cameras with vastly different sensor sizes, I can't help you. The only measure for depth of field that works across cameras with two different sensor sizes is the ratio of distance and aperture diameter, which determines the solid angle of light capture. You're the one that brought up physics, so actually look at the physics instead of using photographer's ready-made formulas without actually understanding them and where they break down.
As for the image that you replied to, it doesn't look any worse at all to the images in the post technically. If you look at the image of the lightning connector, it doesn't even have 2mm of depth of field at a pretty low actual resolution. You can say whatever you want as for the composition and artistic value, that's not what we're talking about.
No, you can't, because you are painfully ignorant on this topic.
Literally, spend 30 minutes with an iPhone and an SLR and you'd be illuminated. Instead you seriously argue that I need to look at the "physics" (which is farcical when you ignore the most important part of a camera, which is the focusing from the lens to the sensor. Dismissing that betrays a complete misunderstanding of optics).
This conversation is clearly futile, but again - spend 30 minutes and actually test your theories. Or, you know, read any single article on the tubes.
Or how about simply ask yourself "why does the iPhone need to do computational bokeh"? 65mm equivalent lens, f/2.2...should be the easiest thing in the world. In SLR world that is bokeh gold.
I have a phone with a macro lens. I have a mirrorless camera. As I told you, what matters for bokeh is the distance to the object and the diameter of the aperture. The iPhone needs computational bokeh because the aperture is 2.4mm wide, whereas one of my lenses has a 40mm aperture. That's why my camera produces more bokeh - the aperture has a wider diameter while the distance to the object is the same.
That is literally the one and only thing that matters. The diameter of the lens, and the distance from the object. Take a piece of paper, draw the lens as a slit, draw the object as a point, and make a line from the two edges of the slit to the point, that continues furhter back. You'll get two triangles. Everything that is contained in those two triangles will be focused to the same point on the sensor. That's why the ratio between the two is what matters. That's why closer objects produce a more out of focus background than objects farther appart. That's what I'm trying to explain to you.
The DoF formula that photographers use does not work for comparisons across two different film sizes.
You understand that cameras don't use a slit, right? Do you understand the optics in a modern camera?
Further my 70mm lens has a smaller aperture than my 35mm f1.4 lens. Yet it has a much smaller depth of field for a given distance. Weird! Lens makers must not know your remarkable "slit lens" trick.
At this point I'm convinced you are either trolling, or have dug so far into the depths of wrongness that you're dedicated to sticking with it. So good luck with that. I'm out of this conversation.
I think you are talking past each other, depth-of-field is dependent on the physical aperture not "F-Stops", which are often also called "aperture". Yes, afaik it's derived from single-element lenses but so are most other measures, and I'd be surprised if a real lens behaved different (at least in the center).
Your 35mm f/1.4 lens has a physical aperture of 35mm/1.4 = 25mm, so the equivalent 70mm lens with a 25mm aperture would have an F-stop of f/2.8. Hmm, can't think of many modern 70mm lenses besides Sigma's 70mm/2.8 macro which should have the same DoF, or if it's a standard zoom they should have equivalent DoF as well (unless it's Canon's f/2 zoom).
The (acceptable) depth-of-field is derived from blur-disk diameter, and the circle-of-confusion, for an object at a certain distance from subject ("point of focus") and relies only on physical aperture and distance to subject as stated (or alternatively, f-stop _and_ focal-length, because "phys. aperture = focal-length / f-stop").
Revolve the entire setup around the axis perpendicular to the slit and you will have a very accurate representation of how a camera-lens system works.
The ratio between distance and focal length only works if the focal lengths are equivalent across the two cameras. Otherwise it doesn't work. That's to say, a 70mm f/2.8 has the same depth of field as a 35mm 1.4 lens if the second is on a camera with 2x crop factor.
Try it out, crop the image of your 70mm lens at f/2.8 and compare it to the image of your 35mm f/1.4 lens and you will get exactly the same image with the same blur (assuming the lenses are exactly 70mm and 35mm at the focus setting, which is not guaranteed due to focus breathing and manufacturers rounding off their focal lengths)
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).
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)-
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.
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.
"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"
It yields a practically perfect comparison of focus. This isn't a trick or handicapping, and the degree of focus/defocus is identical whether that SLR had 10x the resolution. There is utterly nothing arbitrary chosen here, and the amount a tree 10 feet outside the focus is out of focus will be identical on a 12MP SLR or a 24, 48, or 96MP version with the same focal length / f / sensor size.
My point was that it doesn’t matter what resolution we choose as long as we do the calculations based on the same resolution for both the iPhone and the DSLR (and hence with different values for the CoC in each case, given the different sensor sizes). Thus your value for the iPhone’s CoC derived from its pixel size is irrelevant. We can choose any target resolution we like to make the comparison and get the same result (comparatively speaking).
By resolution here I’m talking about what we could crudely measure in megapixels. Say for example that we have a target resolution of 5MP. We then calculate the corresponding CoC for both cameras based on their respective sensor sizes. You’ll find that the CoC for the iPhone will be smaller in proportion to the difference in focal lengths between the iPhone and DSLR. That cancels out one of the factors of f.
Sudosysgen is saying the same thing, but without going indirectly via the DoF formula that you’ve been using.
The CoC for the iPhone is smaller than the ASP-C given the smaller sensor. By choosing the same resolution of an ASP-C sensor, we are calculating for a given level of "good enough for that resolution". It is perfectly comparable level of focus. I have no idea why you are so caught up in distractions.
I calculated the hyperfocal length for an iPhone and an equivalent zoom SLR, at the same aperture. These yield effectively identical degrees of focus from 1/2 the HF to infinity. The iPhone is from 3.2ft to infinity, the SLR is from 27 feet to infinity.
Nothing else matters if you can't tell me why that's wrong. Because it isn't wrong. It's absolutely right. The same zoom level and cropping. MASSIVELY larger focus zone.
If we doubled both dimensions of the sensor, thus doubling the CoC, it would halve the HF. If we instead doubled the focal length it QUADRUPLES the HF. The focal length is a squared factor and outweighs any other component. For a reason.
If you double the focal length you also have to double the sensor dimensions (to get the same angle of view) and hence double the size of the CoC - so you end up with f^2/f = f. That is, you double the numerator in the DoF formula because the CoC has doubled, and quadruple the denominator because the focal length has doubled, with the end result that the DoF halves.
Your mistake is one that’s easy to make and one that I’ve made myself before. We’re not trolling you. You’re just losing track of a factor of f and thereby getting the wrong result.
By the way, I also agree with your overall point about smaller sensor cameras being better suited to macro photography. It’s just that your f512 claim is based on a mistaken calculation.
There is no mistake. Your first paragraph is unfortunately founded on some misunderstandings of optics, however I calculated the hyperfocal length for an equivalent ASP-C 35mm system and an iPhone at the same crop (which anyone with an SLR and an iPhone can replicate in moments). The iPhone has a dramatically higher DoF. There are no mistakes in that calculation. This is the reason why you need computational bokeh. It's why it's so easy for everything to always be in focus. Could someone contrive ridiculous focal length / f-ratio / CoC parameters? Of course they can -- it's just a function with parameters that you punch in, and they can offset. In actual reality, however, short focal length is the primary input into why small cameras feature larger depths of field. Why we talk about the equivalent aperture in the way that we talk about equivalent focal length.
sudosysgen's argument in the end seems to distill down to "yes, but compare it via the equivalent DoF f-stop on the larger camera" which is a short circuit of the entire argument. It is basically saying that AMC is worth the same as Apple if AMC shares were each worth $4636.
That's not how it works. If I take a picture with 2x crop sensor at 100mm f/2 it is going to be exactly the same picture as at 50mm f/4 on a FF camera. Its just how it works. They have proven it using the DOF equation by showing that scaling the CoC factor down with the focal length and scaling the focal length down means you have the same DoF as long as the actual aperture diameter is the same, algebraically. I gave you an explanation of why it is the same because the solid angle is preserved. In the end you're making the typical photographer mistake of misunderstanding crop factor.
You can't use the same aperture. The SLR has to be at a smaller aperture so the diameter of the lens is the same. That way both will gather the same amount of light and have the same amount of bokeh.
That's your issue - you need to use equivalent apertures.
Set sensor size to "custom (NaNx)". Set Custom Sensor to "1". Set focal length to "25mm". Set aperture to "f/2". Set distance to 2m You will find a DoF of 759mm.
Then set Custom Sensor to "0.5". Set focal length to "50mm". Set aperture to "f/4". You will find a DoF of 748mm due to rounding errors in the calculator.
Then if you set custom sensor to 2, focal length to 12.5, and aperture to f/1, you'll find a DoF of 739, again not quite equal due to rounding errors.
As you see, if you double the sensor size, double the focal length, and use an equivalent aperture, you have the same DoF.
The CoC refers to the circle in the pixel that a point will be focused to. The pixels on an iPhone are much smaller than the pixels on a camera. If you use the same CoC for the iPhone, you are referring to many more pixels than on a DSLR.
Therefore, when you use the same CoC, you are asking the DSLR to be dozens of times closer to perfect focus, in pixel terms, than the iPhone, which is why you are calculating outlandish f stop values.
If instead, you have a target that the object must resolve to a pixel with the same resolution on both, you will arrive to an f stop linearly proportional to the sensor size, instead of proportional to the square of the sensor size.
I clearly used completely different CoCs, factoring in the different sensor sizes.
At this point I feel like you are just posting things hoping some future visitor will think that your commitment must demonstrate that you are right. I guess.
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.