is exposure F2.2 (i.e amount of light) on the iphone 5s the same as F2.2 on an SLR

Discussion in 'iPhone' started by whitedragon101, Oct 9, 2013.

  1. whitedragon101 macrumors 6502a

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    #1
    1)
    The iPhone 5s has an F2.2 aperture. Does an F2.2 aperture produce the same exposure whether its on a tiny iPhone sensor or a 35mm full frame?

    2)
    In normal photography when you lower the F number of the aperture the image quality reduces. For example a 50mm F1.8 at F8 produces a sharper image at infinity focus than at its lowest F1.8 setting. How does this work with these tiny iphone lenses? Does quality reduce as you lower the F number ?
     
  2. Mercenary macrumors 6502a

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    #2
    1) no. A dslr has a much larger sensor. Especially if it's a 35mm full frame. Larger sensor, larger pixels, better image capture.

    2). Higher fstops mean the whole image is sharper and the depth of field is increased. Same principles will apply for the iphone but not to the same degree. The 5s is good. But it's never going to give me the same image as my full frame dslr with a bit of canon L series glass.
     
  3. walmartmartyr macrumors 6502

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    #3
    NO, image is usually not sharper at higher f-stops, unless your paying thousands for the lens. sharpest images are usually at 4-5.6 fstop.
     
  4. Mercenary macrumors 6502a

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    #4
    And I do pay thousands for my glass.
     
  5. walmartmartyr macrumors 6502

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    #5
    then you should know better to tell people that higher F-Stops (lower number) means sharper images. Even if the image was sharper, the depth of field is so shallow that a lot of shots will be out of focus due to movement.

    P.S. I have two F2.8 canon brand zooms 70-200 and 17-55mm = $4500
     
  6. deeddawg macrumors 604

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    #6
    True, but only up to the point where diffraction takes over; this means there will be a "sweet spot" of maximum detail within the aperture range, above which detail is lost. See Circle of Confusion.

    ----------

    You two are using the term differently. Common usage in my experience is "higher f-stop" means a larger denominator; i.e. smaller physical aperture.

    BTW what you spent on Canon L glass is relevant only to the size of your wallet and has no bearing on whether you have any actual knowledge.
     
  7. whitedragon101, Oct 9, 2013
    Last edited: Oct 9, 2013

    whitedragon101 thread starter macrumors 6502a

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    #7
    1)
    I know the quality is better ( I have a 5dmk2 with L glass) . What I am wondering is what does F2.2 mean in terms of how much light hits the sensor. i.e If i took 1mm squared on the iphone sensor and 1mm squared on the 5dmk2 sensor at F2.2 would the amount light hitting it be the same?

    2)
    The DOF of F2.2 on an iphone sensor is around F11 35mm equivalent. But I wonder how the F numbers on these small cameras effects the quality. i.e would F3 be darker but sharper ?
     
  8. Mercenary macrumors 6502a

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    #8
    Good for you. Have a cookie.
     
  9. steve-p macrumors 68000

    steve-p

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    #9
    This is true. The sharpness sweet spot for the Nikon 35mm superzoom I use for travel for example is F8. Although the iPhone doesn't have an optical zoom, it is a multi-element lens design, so who knows (or has tested) what aperture is sharpest. Since you can't actually select manual or aperture priority modes, it's a bit moot anyway.

    ----------

    I don't know the answer to that, but the f-number is related to focal length, so is not directly comparable to another system, then there's the difference in sensor size, and the different density of the individual cells in the sensor. Also the sensors may not have equal sensitivity. It's a complex question.
     
  10. parseckadet macrumors 6502a

    parseckadet

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    #10
    I'm going to take a stab at some more technical explanations. But I'm nowhere near a professional photographer, so if I get some of the finer points incorrect please forgive me.

    1: No. F stops are relative to the focal length of the lens. When Apple says it's an f2.2 lens, they're saying the aperture can open as wide as f/2.2 mm where f is the focal length. I'm not sure what the focal length of the iPhone's camera is, but I guarantee you it's nowhere near as long as those on an SLR, or even a point-and-shoot. And don't be confused if you see someone claiming it has a 50mm lens or anything like that. When you see numbers like that, they're stating that it's EQUIVALENT to 50mm on a 35mm frame.

    Let me illustrate with an example. Let's take a 50mm, f2.2 lens on a full-frame SLR. That yields a maximum aperture opening of 22.73mm. Now take a look at the iPhone, which is only 7.6mm wide to begin with. For simplicity's sake, let's assume that full width was the focal length (it's really going to be shorter because you have to have room for the other components, screen, etc.). So a 7.6mm, f2.2 lens would have a maximum aperture of 3.45mm, or only about 15% as big as that on a full frame SLR with a true 50mm lens. So that means much less light will reach the sensor. Also, since the light has a much shorter distance to travel between the lens and the sensor, it doesn't scatter as much, meaning the range of depth of field is not as robust.

    2: I think you're not quite understanding what's going on when you say that the image quality is affected by changing the aperture setting. What you're seeing here is the change in depth of field. Yes, larger apertures (smaller f numbers) have shallower depths of field. But that might be the look the photographer wants. Regardless, producing a narrow depth of field depends entirely on the aperture size. Using my example above, the aperture is wider on the 50mm lens even at f11 than the iPhone's aperture would be at f2.2. Thus the iPhone isn't really going to be capable of producing narrow depths of field.
     
  11. kingalexthe1st macrumors 6502

    kingalexthe1st

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    #11
    The previous poster made some really good points, but I think missed these ones you posted. IMO, the TOTAL light entering the lens will obviously be far less in an iPhone than in a DSLR. But what you asked, as in "is the amount of light hitting 1mm squared on the iPhone sensor the same amount as that hitting 1mm squared in a DSLR?" I'd also reply with "No". My only logic for this is that 'bokeh' at the wide open apertures is the result of lots of scattered light from distant objects. You don't get as much bokeh on the iPhone therefore not as much light. Makes sense?

    In response to your second question, yes F/3 would be darker and sharper. But that's true of any camera, unless I read your question wrong.

    Hope that helps,
    Alex
     
  12. deeddawg macrumors 604

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    #12
    No. You misunderstand bokeh and what creates the effect.

    Think about this: ALL the light hitting the sensor comes through the aperture.
     
  13. kingalexthe1st macrumors 6502

    kingalexthe1st

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    #13
    Illuminate me, please (ha! pun not intended).

    My understanding is bokeh is from light from a distant object having a large aperture to go through, therefore it has spread out more than light that has been reflected by a near object. At high apertures a narrow opening doesn't allow the spread-out light to come through, so you get a crisp image. No?

    Alex
     
  14. deeddawg macrumors 604

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    #14
    Bokeh is merely the name for the very out-of-focus portions of the image. The same light creates the same part of the image, the only thing that makes it bokeh is it being essentially unfocused due to narrow depth of field.
     
  15. Nikola Tesla macrumors newbie

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    #15
    1. physical aperture size (in terms of mm or inches) doesn't depend on sensor size, but the focal length of the lens.

    2. F number, or aperture is not an indication of lens quality. Although it's generally true that SLR lenses are not the sharpest when wide open (like your 50mm @ F1.8). But it's not true that F22 would produce the sharpest image. But keep in mind that this is true because of lens design. Since the aperture is variable, engineers try to optimize the design so the lens is pretty sharp across all F stops. This is very difficult/expensive to perfect, so that's why some stops are sharper than others.

    From what I can tell, the iPhone has a fixed aperture and focal length. I imagine if they actually designed the lens for this specific use, they would have designed around the fixed focal length and aperture to optimize at that point. It would be dumb not to from an engineering stand point. (Curious: Is there a published MTF chart for the iPhone 5S?)

    The 5S is great for what it's meant. If you want a superb image, you need to abandon the phone. You'll want a large sensor with high pixel count and large pixel pitch, paired with a lens with high resolving power.

    Pixel Pitch Example:
    iPhone 5 = 1.4 micron
    iPhone 5S = 1.5 micron
    Canon EOS T5i = 4.3 micron
    Canon EOS 1D X = 6.95 micron

    Source: am Engineer at Canon.
     
  16. hbcubs macrumors member

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    #16
    So true. More expensive glass in no way makes a better photographer. Why anybody feels the need to flaunt how much they've spent on L lenses is beyond me.
     
  17. kingalexthe1st macrumors 6502

    kingalexthe1st

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    #17
    And out-of-focus comes from spread out light. The distance between lens elements is altered to focus different parts of that spread out light. Here we're talking about aperture, which reduces the size of the hole which the spread out light can go through, essentially blocking out all the spread parts of light leaving you with a nice narrow beam from all distances.

    I feel we're having a parallel argument here :)

    Alex
     
  18. deeddawg macrumors 604

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    #18
    Which all has about as much to do with bokeh as denim has to do with paisley. ;)

    Essentially you're grasping the fundamentals but explaining yourself in a mildly contorted manner that leads to the incorrect statement about bokeh suggesting how much light comes through the lens.

    Take a lens at f/2 and focus on an object five feet away with a distant background. Tons of bokeh.

    Same lens and everything else the same, but replace the object with a flat mural that fills the lens field of view while remaining within the depth of field. Everything is in focus, no bokeh.

    No change in aperture. Very different bokeh.
     
  19. elistan macrumors 6502a

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    #19
    Yet another stab at an answer: :D

    1) Yes, I think so. The f-stop number is the ratio of focal length to aperture. So a 300mm lens will have a 136 mm aperture (hugh!) at f/2.2, while a 4.12 mm lens (what's used on the iPhone 5s, I think) will have a 1.87 mm aperture. The brightness of the image projected by either lens, as measured at a single point, will be the same.

    2) Yep, exact same way. (Although it's not correct to refer to the different depth of fields produced by different apertures as "image quality." Shooting at f/1.8 can produce a better quality image than at f/8 depending on what you're after.)
     
  20. GoSh4rks macrumors 6502

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    #20
    Everybody saying anything other than "yes" to #1 is wrong or isn't reading the question correctly.

    Exposure is the same no matter the size of the system. F2.8 and 1/1000s will produce exactly the same exposure (given the same ISO and allowing for any T-stop differences) on an iPhone camera as it would on a 35mm film camera.

    2. Depends on the lens. Some lenses are sharper at F4 than at F8, and others are sharper at F8 than F4.
     
  21. whtrbt7 macrumors 6502a

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    #21
    There seems to be a lot of confusion on this thread. So as a photographer I'll chime in.

    1. F-stop is a calculation based on the focal length and diameter of the entrance pupil. The answer to the first question is "yes" because the formula of F-stop is F-stop number (N) = focal length (f) / diameter of pupil (D). That means that the f/2.2 lens will receive the same amount of light as another 35mm FF lens that is f/2.2. In terms of exposure, exposure time at f/2.2 is the same across cameras including the iPhone 5S camera. What comes out the other end is subject to lens quality, sensor quality, dynamic range, and several other factors. So the photo taken with the same exposure time will have image differences due to the factors mentioned.

    2. To answer the 2nd question, we need to take a look at MTF charts. Lenses have different rates of light transmission at different apertures. This all depends on the quality of the lens. Even crazier still is that not all lenses are created equally. Each lens has a "signature" light transmission even if it has the same MTF chart. Light transmission can also be different at the edges of the lens as opposed to the center. With lower f-stop, it means your aperture is larger and you will get generally more light. Larger apertures also help to create background separation which is what makes some images look like they have a blurry background. The signature of the blur is called "bokeh". Image quality can change with your aperture settings. Depending on what your lens MTF chart looks like, there are normally "sweet spots" in image quality. With the iPhone lens, we would need to take a look at the 5S MTF chart to see at which aperture it is sharpest.
     
  22. whitedragon101 thread starter macrumors 6502a

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    #22
    I do really mean sharpness not depth of field. When I was buying camera lenses for my full frame I spent a whole year looking at MTF sharpness graphs for them. All SLR lenses have low sharpness at their largest aperture which increases usually peaking around F8 then dropping again due to diffraction. eg

    About 1/3 of the way down is the MTF graph
    http://www.photozone.de/canon_eos_ff/472-canon_50_12_5d?start=1
     
  23. whitedragon101 thread starter macrumors 6502a

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    #23
    Aha thanks. That explains why they are never sharp wide open. I always wondered why the image was less sharp on wide apertures. I know about the diffraction problem at the top end but I never fully understood why sharpness dropped off at the bottom end. Simply that it does. So with fixed apertured a F0.5 aperture at infinity focus could be as sharp as an F8 at infinity focus?


    Thanks for the detail guys. I suspect you are flitting between here and the DPReview forum ;)
     
  24. scotrinaf macrumors 6502

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    #24
    I have cheap lenses for my Canon 60D, but they work well for what they do. :) I work for a high quality print shop and it amazes me how many people take pictures with their iPhone and then are incredulous that it can't be used as a full page photo in their college catalog...

    People have no comprehension of the differences (and I'm a beginner) in camera & lens quality and how much it matters when it comes to taking high quality photos...

    My favorite lens, which is next on my list to buy, is a 10-22mm, my current "good" lens for night shots is a 50mm/F1.4, other than that, I only have mediocre lenses, the silver stripe 18-135mm and a gold strip 70-300mm. I seriously need to take photography classes to learn how to maximize my shooting...
     
  25. ElectronGuru, Oct 9, 2013
    Last edited: Oct 9, 2013

    ElectronGuru macrumors 65816

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    #25
    Aperture is a length/width ratio, like 1.8:1, we leave off that last bit because it's assumed. A 1.0 lens is as wide as it is long (a square side profile vs the standard rectangle). The larger the sensor, the bigger the lens must be for the same ratio, so a 2.2 iPhone lens is much smaller than a 2.2 35mm lens.

    Lenses bigger than 2.0 give more 'impressive' results, but achieving those results required more work/experience. I have a 1.2 lens and can finish a session sweating from the work needed to achieve a series of well focused shots of moving subjects. The DOF is so thin, one person's eye can be focused with the other not.

    By using 2.2, apple is saying the lens is bigger and will yield better images. But this is all relative to the size of the sensor. Smaller sensors still struggle to keep up with larger sensors, but like all tech, get better every day.
     

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