Originally posted by abhaskare Yes, it is quite surprisinhg how they manage f1.8 in such a small size.
Pentax K-5 II vs Nikon D3400
One reference says focal length is actually 3.8 mm!
What Kunzite is trying to say is that it's actually extremely easy and cheap to make tiny bright aperture lenses and extremely hard and expensive to make big bright lenses.
If you take that iPhone lens design and scale it to full frame size, every dimension must scale up by about a factor of 7. But that means the surface area grows by a factor of 49 (7 squared) and then volume increase by a factor of 343 (7 cubed). That scaling creates huge costs. And the elements of the full frame lens would have 49 times more the surface area that must be perfectly dimensionally controlled. And the bigger lens would require over 343 times as much ultrahigh-quality optical plastic as the iPhone lens. Not only does the bigger lens require a lot more high-cost material but also it's much harder to maintain optical uniformity in a bigger volume -- if there's one tiny swirl of less dense material because of the way the element polymerized or solidified, the lens is ruined.
Moreover, the six element design of the iphone which works so well at that tiny scale would suck on full frame. All the high-quality, bright-aperture lenses for full frame cameras tend to have twice as many elements as that iPhone design.
Finally, those iphone lenses are manufactured in volumes of tens of millions of units. Apple's suppliers can afford to spend tens of millions of dollars on very specialized manufacturing equipment and automation that makes the unit prices cheap.
Similar scaling issue affect increasing the aperture of a lens design from f/2.8 to f/1.4 -- it forces the designer to create more lens elements that are larger in every way and hence much more expensive.
Everything about large-format, large-aperture camera lenses makes them much harder to make and much more expensive.