Cell Phone Tele Lens

Discussion in 'Beginner Questions' started by fmueller, Feb 18, 2018.

  1. So I finally got a cell phone. I was holding out to be the last person on earth to get one, but my brother thwarted my plan by giving me a HTC M8. Having started with film and a Minolta XD-7, today I have a 7D and a full set of EOS lenses. I also have a little Lumix, if I want to travel light, but I expect to have the cell phone always with me.

    I am no newcomer to photography, but I am keen to figure out the whole cell phone thing. The camera is actually quite nice, but the digital zoom is terrible. It's so bad that it's always going to be better to crop later than to use the the tele zoom function in the camera.

    I've seen that auxiliary lenses for cell phones are available. The lens is pretty wide, and the macro capabilities are good enough. If I need more, I can always take a proper camera. But the tele is awful. Should I just keep on cropping, or would it be worth my while to look for an attachable tele zoom lens? It would have to be small, so it can rest permanently in a pocket. If I want to lug gear around, I won't rely on the cell phone. Does anybody have experience with this and can make some suggestions?
     
  2. I appreciate both the ease and limitations of the cell phone as a camera. I have found what you have, that using the zoom really degrades quality. So I don’t use it. I crop later if necessary, but generally try to crop as little as possible, as even cropping affords little latitude in terms of quality. I want my phone camera to be basic and simple, so haven’t thought about an attachable lens. I’ve really enjoyed shooting with my iPhone and sometimes find that being challenged by the limitations can be inspiring.
     
  3. Hi Fred, yes I hear you. For many years I have shot slide film with an old Minolta and a 50mm 1.4. It was all I had, and I've got many nice shots from this time. You had to take what you got out of the camera. In many ways, the cell phone is better! I guess I was mainly trying to justify buying yet another gadget. ;-)
     
  4. A "digital zoom" is exactly the same as cropping, usually with some image rescaling applied afterwards, so you're right that it won't give you better results. This is less true of some recent phones that have two lenses of different focal lengths. There have historically been some phones with mechanical zooms, but they're necessarily quite big and chunky.

    As you say, there are some cheap optics available to attach over the lens of some phones. They're not going to be optically brilliant and may get in the way of a case, but I'll sure they beat digital zoom, at least at high factors. Some companies (notably Sony) have sold digital camera sensors and lenses that are driven through a phone, but once you're doing that, you may as well use a compact camera.

    At some point, anything the size of a phone is going to be limited by making the sensor and lens tiny. Modern cell phones have remarkably good cameras considering the photons they're actually capturing, but there's still a great deal to be said for anything with a bigger sensor and lens.
     
  5. Andrew, I think you have given me the explanation why the digital zoom in camera is so much worse than simple cropping in post processing. Presumable digital zoom scales the image up after cropping, and that degrades quality much more than simple cropping. I knew optical zoom could not be better, but I was surprised to find it so much worse.

    There don't seem to be any decent reviews of these auxiliary lenses. People make lists of the 10 best lenses for cell phones, which contain anything from fish-eye and macro over tele to a polarizing filter. That's like making a list of the best tools and rating a screw driver next to a fork lift. Tele lenses seem to range from 2x all the way up to 18x. There are 2x lenses for $100, and 18x ones for $10. I think anything 8x and over might suffer from serious vignetting, and like the old T-mount lenses, they are reasonably sharp at the center with a steep fall off towards the edges. Presumably the 2x lenses offer the best quality, but I won't spend $100 on one. Maybe for $25 I would give it a shot. My phone has a 28mm equivalent lens. A 2x converter would give me roughly a good old standard lens, which would be nice. There are also 3x converters that would make a nice portrait lens with my phone camera. Birthday is in a couple of months!

    If anybody working on the learning section of Photo.net is reading this, a decent review of the optical qualities of auxiliary lenses for cell phones would be sure to find a large audience!
     
  6. Personally, I never quite got these extensions for smartphones. They're fiddly to attach (and in some cases fiddly to keep them on too), and they do add some bulk, even if little, plus slow down. While the nice thing about smartphone-photography is the quick, impulse shot - quick, and hence the device itself should stay simple. Sure there are different uses, but the "handling" of a smartphone as camera does impose its limits too. It's hard to keep them still, especially the larger ones, and even harder to do so while puhsing a button or the screen to take the photo. A smaller angle of view will amplify these effects sufficiently.

    In addition, the sensors on smartphones have incredible density, which means the resolution of the lens is being tried enough. Adding additional glass-air surfaces in front will not improve things. So I'm not even that sure they'll beat cropping, unless indeed taking those with a very high magnification (but then the handling becomes a seriously big issue). Vignetting might be an additional issue, but frankly I doubt it'll be the biggest problem.
    So to me, both in usability and in technical soundness, the whole idea of clip-on lenses fail to make sense.
     
  7. fmueller: The arguable advantage of digital zoom is that the zoom is being applied before JPEG artifacts are affecting the image. But I doubt the algorithm is especially complicated (I don't know what my employers do). There are enlargement options that are vaguely clever (such as the neural net ones at resize.io, although the experiments I tried there didn't work very well), but I would expect most approaches just to perform a traditional reconstruction filter. I'm a little surprised that you're finding it significantly worse, but I guess it depends how you're enlarging the cropped image yourself. (At the pixel level it'll definitely be worse, of course, but if you shrink a digitally zoomed image back to its cropped size, I'd expect a small improvement because of the JPEG artifact argument - but that depends how the resizing is done in each direction.)

    Auxiliary lenses are usually generally very much made to a budget, and I strongly doubt they have the degree of alignment in the attachment mechanism which we'd expect from an SLR lens. On the other hand, it depends what you're comparing against - digiscoping by holding up a phone behind a telescope isn't so unreasonable, and certainly a lot better than you'd get from a crop. I would strongly expect the longer zooms to be quite large and unwieldy for permanent attachment, though; as Wouter says, if your phone is as big as a compact, you'll stop having it with you. I rely on my RX100 as something that fits in a pocket and takes relatively decent photos, but I admit many photos of my little old cat were taken on my phone, because that's all I could reach when she was actually on me.

    Owning a relatively rare phone (I have a Nexus), I've not gone hunting for accessories, so I'm not well positioned to advise. I'd definitely find the phones with an integrated (relatively) telephoto lens to be more plausible than external attachments, but I'm willing to be surprised.
     
  8. > So I'm not even that sure they'll beat cropping

    Wouter, neither do I. I get a feeling nobody knows, or at least it's not as easy finding this information online than I would have expected.
     
  9. My Apple 8+ phone has an internal dual lens setup; the 1x "normal" lens being approx. 28mm (35mm eqiv.), with a "2x" lens at 56mm (35mm eqiv.). I get amazing photos with this camera/phone. It's funny how the 2x lens feels like a telephoto after using the 1x.
     
  10. paul ron

    paul ron NYC

    phone cameras are getting better over the years. i even see news reporters using them.

    have you seen this?...... a set of attachment lenses.


    Pixter Pro Pack

    perhaps one day they will make a camera with a built in phone.
     
  11. The focal length of the lens dictates the image size. A “normal” lens is one that yields an image with a perspective that mimics the unaided human eye. As a rule of thumb this will be a focal length about equal to the corner to corner measurement of the image sensor used. Most telephone built-in cameras have a focal length that is slightly shorter than “normal”. Such a lash-up is termed wide-angle. The realm of telephoto starts at twice the focal length of “normal”. Phone makers avoid because it would make the phone too thick.

    If a camera is positioned so it is peering through binoculars or telescope, a magnified view is realized. This is the principal of the telephone supplemental lens. You could procure a monocular and hand-hold your phone so it is looking through a monocular. You might be surprised as such a lash-up will yield good results. Plus, you can use the monocular to get a magnified view, good for the beach and theater.
     
  12. They did. (Even Nikon sort-of did, although it didn't actually have cellular connectivity.) It makes for a very unwieldy phone and not necessarily a very good camera, though.

    Well, a bit. To elaborate, since this is the beginner forum and people might read it...

    Humans can, according to Wikipedia, see about 210 degrees horizontally (yes, behind you) and about 150 degrees vertically. It's been suggested that there's a "cone of attention" about 55 degrees across. A 43mm lens covers 45 degrees (22.5 each way) on the long axis of a full-frame camera; a 52mm lens does the same for the diagonal. Mostly, "normal" shouldn't look distorted, which means that the viewpoint from which you're viewing the image relative to its size should resemble the lens nodal point's view of the sensor/film plane. If you take a shot with a 14mm lens on full frame, print it as a 40" (diagonal) poster and view it from 14" away (from the centre), it won't show "perspective distortion". Practically, for comfortable viewing, most people would view a picture so it would cover about 45 degrees of view, so we think of that as "normal". But there's enough slop in the way eyes work that the exact number doesn't matter much.

    The eye is relatively sensitive to perspective distortion with wide angles - things start to look a bit funny by 35mm, and very whacky by 24mm, especially if there are humans in the image. You can see a bit of distortion as lenses get longer ("telephoto", of course, technically refers to a design that's shorter than its physical focal length, but it's popularly abused to mean "long") bit the effect is relatively subtle - people look a bit "flat"; ears look larger, noses look shorter. (All this is a function of subject distance, not focal length, but they're related if you fill the frame with the subject.) It's been said that people remember what other people look like from about 15' away, which corresponds to about a 90mm lens (for a 6' subject filling the long edge of a frame) or 135mm for a a 4' posed upper body shot - the range of a conventional "portrait" lens.

    Putting a long lens in a cell phone does, indeed, make it thicker - no matter how small your sensor is. And since you probably want it to receive a reasonable amount of light, there's a lower limit to how small you want to make the sensor. More practically, though, if you put a wide lens on a phone and want a tighter crop, you can easily do that digitally (at some loss of resolution). If you put a long (telephoto) lens on and wanted a wider image, you can only fix that by stitching shots together, which is at best a little awkward and at worst (for moving subjects) impossible.

    A moderate wide angle is useful for taking shots of small groups of people, especially if you're only at arm's length from them. It's also useful for landscapes. Putting a second camera on a phone gives you a better quality alternative when you wanted to capture a narrower field of view (especially for portraits), but I doubt the wide-angle lens would go away even if people played with folded optics to try to make it fit.

    The idea of adding a supplementary lens is quite reasonable, but my cynicism about them comes partly from the budget dedicated to their production (cellphone cameras themselves have quite good optics, but they make millions) and the limitations of aligning the components - conventional lenses have very precise alignment requirements, and slapping a bit of plastic on a phone case is unlikely to meet them.

    On the other hand, digiscoping is extremely useful. The image quality, especially at the edges of the frame, is unlikely to get close to what a dedicated long lens will do, but it's a vast improvement over enlarging the tiny number of pixels that cover the field of view with the integrated wide-angle lens. You're also likely to be gathering a lot more light. But there's also a difference between a small bit of plastic in a vague lens shape and a few large lumps of optical glass built without (such tight) size and cost constraints.
     



  13. About "normal":


    Mounting a lens with a focal length about equal to the diagonal measure of film or digital sensor is the industry standard for “normal”. Such a lash-up delivers a diagonal angle of view of 53°. This is true regardless of the format dimensions. Additionally, this is the angle of view most often published. If the format is the classic rectangle of the full frame, the horizontal angle of view is 45°.


    You should also know that a lens delivers a circular image that is cropped by a mask to the format size of film or sensor. Typically a lens with a focal length about equal to the diagonal measure of this rectangle will deliver an image that will be reasonably uniform as to illumination (no serious vignette). If the lens is shorter than this measurement, a vignette is likely unless the lens is designed for wide-angle use.


    These are the key reasons that a focal length about equal to the diagonal measure is considered “normal” as to angle of view.
     
  14. Alan is of course right that there's a consensus on what a "normal" lens is for any format (I was only trying to clear up any confusion about what the eye's "field of view" was, since that explanation is often rolled out as a "normal" lens explanation without much context). Small differences in focal length are ignored, though - to most people, 50mm is "normal" on full frame, but most would consider Nikon's 45mm pancake lens and their 58mm lens both to be near enough to 50mm to be "normal".

    I'd not heard the vignetting argument before, although I appreciate that it's historically been a factor. I'm not sure of the extent to which it applies with modern lens designs - for example, the wide-angle Sigma 24mm f/1.4 (and even more so the moderately wide 35mm f/1.4) show less vignetting than Nikon's venerable "normal" 50mm f/1.4 AF-D. (Just in case this scares people off wide-angle lenses!) It's certainly true that the longer a simple lens, the less vignetting is a factor, and that vignetting is usually not significant at longer focal lengths.

    One other observation is that lenses which are wider than "normal" typically require a retrofocal design in order to clear the mirror box of an SLR - but "normal" lenses predate SLRs, many modern longer lenses (such as the 50mm Sigma Art and 55mm Zeiss Otus) have a lot in common with retrofocal designs, and the size of the mirror box in crop-sensor DSLRs is often inflated for compatibility: a 35mm lens may be "normal" for a Nikon DX DSLR, but it still needs to fit on a mirror box designed for a full-frame camera. So it's not an exact observation. :)
     

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