| HN Mirror

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.

"I can't help you"

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.

altarius 1715 days ago

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)

foldr 1715 days 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).

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)-

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 1715 days 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.

"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.

foldr 1715 days ago

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.

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.