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Thread: focal length

  1. #1

    Default focal length

    I wonder does it make sense for PNS camera manufacturer to print their wide and tele figures in non 35mm format .. tat means it's not making sense to compare different cameras cos of different chip size?
    why dont they print the 35mm equivalent focal length on the camera itself

  2. #2
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    Default Re: focal length

    Actually I have been wondering that too. Perhaps the manufacturers feel that the target group is different, that they will not understand what it means by a 35mm lens? More often than never, consumers are more attracted to 10x optical zooms rather than 35mm -350mm focal length.

  3. #3

    Default Re: focal length

    i suppose its a matter of the 'actual' focal length of the lens

    say 8mm on a Pns, which is abt 40mm on 35mm format, is physically 8mm, not 40mm
    even though it seems like 40mm due to the small sensor size

    like even DX lenses; the 12-24 is not called the 18-36 even though it gives u an 18-36 focal length range, in 35mm format

    anyway i suppose many PnS users (but not all, definitely) dont really understand the 8-24mm f/2.7-3.6 on their cam. like cantaresg said, optical zoom is impt, the higher the better, more attractive still, megapixels

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    Default Re: focal length

    if they print 28-105mm on the PnS, people will start wondering why my lens so small and yours so big?(compare to dSLR)

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    Default Re: focal length

    Quote Originally Posted by gonefishing View Post
    I wonder does it make sense for PNS camera manufacturer to print their wide and tele figures in non 35mm format
    I'm not sure what you mean with "35 mm format". Focal length is a physical parameter of a lens that is independent of the camera the lens is attached to.

    A household light bulb in Singapore runs on 240 volts, while a small hand-held torch may run on 3 volts. Should one thus "convert" the 3 volts of the torch and claim the two AA batteries produce 240 "equivalent" volts? This would obviously be utter nonsense.

    "Converting" focal lengths to "equivalents" is exactly the same kind of nonsense. The widespread (ab)use of this practice merely demonstrates that for a significant part of photographic "experts", something went seriously wrong during their secondary school years.

  6. #6

    Default Re: focal length

    well, I think its a matter of convenience to convert into "35mm format".. cos its the most widespread format used, to give users a sense of what the FoV would be like..

  7. #7

    Default Re: focal length

    Quote Originally Posted by LittleWolf View Post
    I'm not sure what you mean with "35 mm format". Focal length is a physical parameter of a lens that is independent of the camera the lens is attached to.

    A household light bulb in Singapore runs on 240 volts, while a small hand-held torch may run on 3 volts. Should one thus "convert" the 3 volts of the torch and claim the two AA batteries produce 240 "equivalent" volts? This would obviously be utter nonsense.

    "Converting" focal lengths to "equivalents" is exactly the same kind of nonsense. The widespread (ab)use of this practice merely demonstrates that for a significant part of photographic "experts", something went seriously wrong during their secondary school years.
    there is no real link between your example and focal lengths - for the second it is a matter of relative perception, i.e. the view seen at a particular focal length, say 15mm, on one camera, should be more or less equivalent to 15mm on another, when special lenses like fisheye are taken out of the equation.

    the truth is, when a p&s consumer camera gives 100mm in terms of 35mm film terms, a dslr will also give 100mm in term of 35mm film terms and they would be the same thing. this is different from 240v versus 3v. same as measurements. i don't think anything went wrong, unless you can explain further - it's like the SI unit system, everyone has a "ruling" scale so that comparisons can be made.

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    Default Re: focal length

    Quote Originally Posted by J-Chan View Post
    well, I think its a matter of convenience to convert into "35mm format".. cos its the most widespread format used, to give users a sense of what the FoV would be like..
    Except the field of view is not measured in millimetres, but angles (or sometimes the tangents of angles). If you look through the viewfinder of a SLR equipped with a 50 mm lens, where do you see anything resembling 50 mm?

  9. #9

    Default Re: focal length

    its more for visualisation sake, cos its something most ppl can relate to.. like if I told someone the height of the A380 is 24.1m compared to telling its 7 storeys high, 7 storeys is much easier to visualise than the absolute value..

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    Default Re: focal length

    Quote Originally Posted by night86mare View Post
    there is no real link between your example and focal lengths
    It is entirely comparable. A 3 V lightbulb may have the same perceived brightness as a 240 V lightbulb. That doesn't mean converting the voltage makes any sense.

    i don't think anything went wrong, unless you can explain further - it's like the SI unit system, everyone has a "ruling" scale so that comparisons can be made.
    I think you will agree that a millimetre is a millimetre in the SI system, and doesn't "scale" to be sometimes a bit more and sometimes a bit less. Otherwise, I could make a lot of money selling gasoline by "converted" litres at unbeatable prices.

    I'm not sure about the legal situation in Singapore, but in industrialized countries there are generally laws on units and measurements. Claiming a different focal length than a lens really has would be illegal and, if e.g. a camera is advertised with such a statement, also fraud.

  11. #11

    Default Re: focal length

    Quote Originally Posted by LittleWolf View Post
    Except the field of view is not measured in millimetres, but angles (or sometimes the tangents of angles). If you look through the viewfinder of a SLR equipped with a 50 mm lens, where do you see anything resembling 50 mm?
    well, it can be easily calculated from the focal length in 35mm film terms
    what the field of view is

    these days when i look at things i don't go
    "it's a 125.6 degree fov!"

    i go like, "this must be 10mm or so"
    i'm sure you do as well

    sometimes, conventions are silly, definitely, but they work, and that's why they stay

  12. #12

    Default Re: focal length

    Quote Originally Posted by LittleWolf View Post
    It is entirely comparable. A 3 V lightbulb may have the same perceived brightness as a 240 V lightbulb. That doesn't mean converting the voltage makes any sense.

    I think you will agree that a millimetre is a millimetre in the SI system, and doesn't "scale" to be sometimes a bit more and sometimes a bit less. Otherwise, I could make a lot of money selling gasoline by "converted" litres at unbeatable prices.

    I'm not sure about the legal situation in Singapore, but in industrialized countries there are generally laws on units and measurements. Claiming a different focal length than a lens really has would be illegal and, if e.g. a camera is advertised with such a statement, also fraud.
    hogwash - perceived brightness has nothing to do with science
    in the case of converting p&s focal lengths to 35mm film terms at least there is an exact method to do it based on sensor size, for your example it's all "perceived", which totally throws it out of the window as a null comparison

    for example, when you wish to gather statistics about someone's tastes, do you look at what they eat, or what they perceive they eat?

    er- i think you're just playing devil's advocate for the sake of... well playing devil's advocate. once again, your litre of gasoline example is totally wrong. if a manufacturer tells me that a p&s cam gives me 35-350mm focal length in 35mm film terms, it is what i get, there is no "more or less" in the equation

    heck, do you even know what you're talking about here? because you seem confused.

    on the legal point, rendered null once you throw in the fact that they could easily defend themselves by ensuring that they state that it is in terms of 35mm.

  13. #13

    Default Re: focal length

    just to avoid confusion for any confused soul reading this thread and not understanding it, perhaps littlewolf should read too

    i quote:

    Focal lengths are usually specified in millimetres (mm), but older lenses marked in centimetres (cm) and inches are still to be found. The angle of view depends on the ratio between the focal length and the film size. Due to the popularity of the 35 mm standard, lenses are often described in terms of their "35 mm equivalent" fields of view. This is the difference between a normal lens (e.g. 50 mm), wide-angle lens (e.g. 24 mm), and telephoto lens (e.g. 500 mm). This is particularly common with digital cameras, which generally use sensors smaller than 35 mm film, and so require correspondingly shorter focal lengths to generate equivalent images.
    source

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    Default Re: focal length

    Quote Originally Posted by night86mare View Post
    heck, do you even know what you're talking about here? because you seem confused.
    I'm not confused; maybe you have a problem with comprehending what I wrote. I can assure you that I know quite well what I am talking about. But I'm the first one to agree that this is not always popular with the masses that rather believe in quackery and junk science.

  15. #15

    Default Re: focal length

    Quote Originally Posted by LittleWolf View Post
    I'm not confused; maybe you have a problem with comprehending what I wrote. I can assure you that I know quite well what I am talking about. But I'm the first one to agree that this is not always popular with the masses that rather believe in quackery and junk science.
    well, then instead of giving totally unrelated stuff like

    "assurances" and "name calling" - kindly provide refuting points

    for someone who claims that he is "logical" and projects an "enlightened, allknowing" attitude, you definitely do not provide much logic in the latest post, merely emotive arguments with no basis other than the reassurance that you know what you're talking about

    prove it, instead of coming up with some form of african witch doctor science that only you can understand - i'm sure you'd say something if i told you that the sky was going to fall down today, and assured you that i knew quite well what i was talking about, and the masses that believe in quackery and junk science will just die

    to make things easier for you, here are a few questions:

    a) do you not agree that fov and in 35mm terms can be easily translated to each other?
    b) do you not agree that fov is what people roughly want to know, really want to know instead of some small camera's "focal length"?

    if you agree to a and b, then why are you arguing, that is a further question, which i guess no one has an answer to
    if you disagree, explain why instead of giving unrelated examples, and claiming that it is junk science. thanks - and if you explain that it is because converting this and that is not equivalent, explain WHY this is so, instead of repeating yourself, since i had already refuted that
    Last edited by night86mare; 17th October 2007 at 07:01 PM.

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    Default Re: focal length

    Quote Originally Posted by night86mare View Post
    well, then instead of giving totally unrelated stuff like

    "assurances" and "name calling" - kindly provide refuting points
    Referring the statements of reader "night86mare" in the discussion on "focal length", we would like to clarify the following.

    I'm not aware that I called anyone here names. I think my points have been spelled out pretty clearly. If you don't afford my assurances some credibility, then I don't see how you would believe anything I would write further on, and any discussion would be futile.

    You're free to believe what you want. You can even believe in fantasy focal lengths if that floats your boat. I don't depend on convincing you of anything. I am just as free to not waste my time to force-feed a basic scientific concept to someone who refuses to accept it.

    We thank the writer for his feedback and his interest in science education. We'd further like to assure the general public that we remain committed to scientific outreach for those who are willing to listen.
    Last edited by LittleWolf; 17th October 2007 at 07:46 PM.

  17. #17

    Default Re: focal length

    i rest my case

    more null arguments with no refutation of counterpoints to points, but conclusion that he is correct

    this is our society today
    we are such a bunch of thinkers

  18. #18

    Default Re: focal length

    Chill guys! Don't need to get so flustered over a camera!

    IMHO, P&S cameras are bought by people based on price, number of megapixels, big size LCD, and more zoom! hahahs. Me being one of those stupid people last time.

  19. #19
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    Default Re: focal length

    Quote Originally Posted by night86mare View Post
    hogwash - perceived brightness has nothing to do with science
    in the case of converting p&s focal lengths to 35mm film terms at least there is an exact method to do it based on sensor size, for your example it's all "perceived", which totally throws it out of the window as a null comparison

    for example, when you wish to gather statistics about someone's tastes, do you look at what they eat, or what they perceive they eat?

    er- i think you're just playing devil's advocate for the sake of... well playing devil's advocate. once again, your litre of gasoline example is totally wrong. if a manufacturer tells me that a p&s cam gives me 35-350mm focal length in 35mm film terms, it is what i get, there is no "more or less" in the equation
    heck, do you even know what you're talking about here? because you seem confused.

    on the legal point, rendered null once you throw in the fact that they could easily defend themselves by ensuring that they state that it is in terms of 35mm.

    That is the truth of it folks .... do some reading and I think you will find the same.

    Many people that buy digital cameras be it DSLR or otherwise, had at some time a film camera.

    Of those people, many had cameras other than instamatics and were aware of the lens.

    I come across this daily with customers.

    They want to know what the focal length of a camera compares to what they used in their film times.
    Time, is an effortless construction :)

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    Default Re: focal length

    Quote Originally Posted by LittleWolf View Post
    It is entirely comparable. A 3 V lightbulb may have the same perceived brightness as a 240 V lightbulb. That doesn't mean converting the voltage makes any sense.
    Say let me use this as an example.

    When you say that bulb A and bulb B has a similar brightness, you are saying that they have similar output power, whether they are running based on a 3V lightbulb or a 240V lightbulb.
    So let's assume that both bulb has 240W effective power. Thus a 3V lightbulb runs with an equivalent of 80A of current, and 240V bulb runs with a 1A of current. So by saying that both bulbs are equivalent brightness, you need to first convert them in terms of power and compare objectively.

    Similarly, for a PNS camera and a DSLR camera, in order to compare the field of view, you need to convert them to something comparable. So over the past years, the photographers have decided to adopt the 35mm format for fair comparison.

    So just as on lightbulbs, you publish the output voltage for comparison of consumption and brightness, why can't we publish the equivalent 35mm focal length for comparison? I think that is the question.

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