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Discussing Aperture equivalency (or something like that)

Discussion in 'Open Gear Talk' started by dalethorn, Feb 23, 2016.

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  1. dalethorn

    dalethorn Guest

    Clarification, please: The lens says 6.7-18 and f1.8-2.8. I've understood the conversion to 135 effective focal length for years, but this is the first time I've seen a conversion on the aperture. Does this mean that the effective aperture is f4.9 for manual shooting based on a fixed ISO and shutter speed? I've never heard of that before.
     
  2. serhan

    serhan SC All-Pro

    May 7, 2011
    NYC
    The lens is 6.7-18mm which is equivalent to 18-50mm 135/FF. Aperture is similar eg f1.8-2.8 has f4.9-7.6 equivalent of 135/FF dept of field... 1" sensor has 2.78x multiplier to 135/FF so you will have 2.78 stop aperture difference as well.

     
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  3. dalethorn

    dalethorn Guest

    I see what you're saying the aperture DOF equivalent, but my pro photog friends say that the actual and effective aperture for exposure is what's on the lens, and not an equivalent.
     
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  4. serhan

    serhan SC All-Pro

    May 7, 2011
    NYC
    He is correct for the lens, but not for the camera+lens combo. If you consider the sensor size, the FF sensor gets 2.7 stops more light... Compare the football field filled with balls (light photons) to basketball field filled with balls (light photons) or put a bucket vs small glass under rain and which retains more water... Light is similar, the bigger sensor area gets more photons for the same exposure.

     
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  5. bartjeej

    bartjeej SC Hall of Famer

    Nov 12, 2010
    bart
    In terms of settings (the correct iso and shutter speed to match with the aperture in order to get a correctly exposed image), f1.8 is f1.8 is f1.8. As serhan indicated, that's light density. In order to know the total amount of light gathered (which impacts image noise, dynamic range and color accuracy), you need to compensate for the difference in sensor sizes. By applying the crop factor to the aperture, you're saying: the resulting image will be the same as a full frame lens with an 18mm lens, using f/4.9, and boosting the iso by almost 3 stops (crop factor of 2.8 would make it 3 stops above 1) to compensate for the slower lens compared to this compact. So an image at 6.7mm f/1.8 1/10th shutterspeed and iso 100 on the DL should have the same field of view, DOF, noise, dynamic range, and color accuracy as a full frame camera at 18mm f4.9 shutter 1/10 and iso 730 (iso 100 times almost 3 stops sensor size difference).

    Of course the one thing we don't know is how well the sensor handles that total amount of light hitting it, and that's mostly a generational thing that can't be captured in an easy formula. So equivalent apertures give you a way to compare expected image quality across different sensor sizes, assuming both sensors are roughly of the same generation. The expected dof can be compared directly, since that's not dependant on the sensor.

    Tl;dr: actual aperture compares settings, equivalent aperture compares resulting image quality and dof across platforms.
     
    Last edited: Feb 24, 2016
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  6. pictogramax

    pictogramax SC Top Veteran

    978
    Aug 18, 2011
    Belgrade, Serbia
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  7. dalethorn

    dalethorn Guest

    But if I shoot the photo with the same settings as a full frame camera, except with the small camera I open the aperture 3 additional stops, I'm overexposed by 3 stops. So in spite of the photons argument, you seem to be giving bad advice.
     
  8. Luke

    Luke Super Moderator

    Nov 11, 2011
    Milwaukee, WI USA
    Luke
    Dale, I am probably the dumbest one in the room (just regarding understanding this camera stuff, mind you :wink:), but if you read the article that Milan shared above, I think you will get the point of Serhan's post....... in particular the part labeled (really helped me)......
    Aperture and Noise Ratio – Or: this is where I learned to stop caring

     
  9. bartjeej

    bartjeej SC Hall of Famer

    Nov 12, 2010
    bart
    Dale, see my post above. In terms of settings, small sensors and big sensors are the same. It's just that the image from a big sensor, all settings being equal, will look nicer since there is more total light to work with. How much nicer is determined by the crop factor, and that's where equivalent apertures come in. They basically tell you how far you'd have to stop down a full frame camera to get the same dof. Ofcourse stopping down the lens requires boosting the iso to keep the same exposure. Since the aperture and shutter speed determine how much ligh reaches the sensor, stopping down the full frame camera's lens to the equivalent aperture of the smaller camera (in this case f/4.9) also means the total amount of light reaching the sensor is reduced to the exact same amount that's reaching the smaller camera's sensor at f/1.8. with an iso boost keeping the exposure the same. If both sensors receive the same amount of light, they should show roughly the same amount of noise, dynamic range and color accuracy, assumin both sensors are equally efficiënt.

    As Milans article correctly argues, none of this matters when you have any camera in your hands and you're out shooting. When comparing different camera's you might want to buy, equivalent apertures tell you how they compare in terms of dof and total light gathered
     
    Last edited: Feb 24, 2016
  10. dalethorn

    dalethorn Guest

    I got all of that 2 posts ago, but the thing that wasted time here was injecting a factoid I'd never run into before, just to explain what everyone already knows, i.e. that bigger sensors gather more light at same settings.
     
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  11. serhan

    serhan SC All-Pro

    May 7, 2011
    NYC
    If you understand it, all it matters. Sorry to confuse you, but what I tried to tell you is explained here:
    Depth of Field and the Small-Sensor Digital Cameras
    "So the bottom line - and all you really need to know - is that DOF is inversely proportional to format (sensor) size."

    or
    Background blur and its relationship to sensor size

     
    Last edited: Feb 24, 2016
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  12. dalethorn

    dalethorn Guest

    The sensor DOF issue is pretty well known among photographers, but not so much beginners and intermediates. Which makes it important to discuss on photo forums. The other issue can never be helpful, unless you're trying to inform a full-frame user of what he already knows, ahead of him selecting a smaller camera for casual use.
     
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  13. bartjeej

    bartjeej SC Hall of Famer

    Nov 12, 2010
    bart
    It can be useful for anyone choosing between camera's with different sensor sizes, if they wish to know just how the differences in sensor size and lens speed work out on balance. Any valid comparison needs a reference point, and since everyone is using full frame as as lens field of view reference point, it makes sense to convert to full frame equivalent when comparing dof an total light gathering too.

    But alas, wish lists... I think nic made a good point that travels should be higher on the wish list, and Ive been looking into Sweden recently... but really when it comes to travel, there are more places that I would like to see than there are likely to be days in my life ;-)
     
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  14. dalethorn

    dalethorn Guest

    I'm up to a dozen pros now asking about this, and like another person said here, it's not useful because it makes no sense at all, and because nobody references it. I've been on a lot of photo forums, and there's no track record on such a thing. Perhaps you could show where those references are on a couple of pro photo forums.
     
  15. bartjeej

    bartjeej SC Hall of Famer

    Nov 12, 2010
    bart
    Well, for one, there's DPR

    DL or No DL? What you need to know about the Nikon DL compacts

    ^that, and any other enthusiast zoom compact reviewed / discussed by DPR in the last 2 years or so...
    What is equivalence and why should I care?

    Several other websites have referenced it as well; some to argue that they are useful, some to argue that they're not.

    For two, all the criticisms are basically "sensor efficiency isn't only related to size", but if you read my posts, that's exactly what I said too.

    For three, as I indicated, sensor efficiency is completely irrelevant when it comes to determining DOF, which is what equivalent aperture is also used for. So even if you consider equivalent aperture irrelevant for total light purposes (it is most definitely NOT irrelevant, it's just not the ONLY determinant), it's still relevant for DOF purposes.

    Maybe the pros you consulted don't consider buying different formats that often. Maybe they know from experience what the difference is going to be, so they don't need a formula. Maybe they just don't understand equivalent aperture; being a good photographer doesn't require understanding this stuff, which, as I said 2 or 3 times already, is relevant for choosing a camera, not for using the one that's in your hand. Whatever the case, equivalent apertures are pure logic. Use them to your advantage if you like, ignore them if you like, I don't care; the phenomenon they describe is still there, and still relevant for the purposes I described.
     
  16. dalethorn

    dalethorn Guest

    I already covered DOF as have others - there's no need to beat that dead horse. The point about the Aperture equivalence is, and although you have now found references, is that it's:

    1) Completely useless. Not relevant for choosing a camera outside of DOF.
    2) Confusing to pros and amateurs.
    3) Suggests to pros what they already know, but can't use in that expression.
    4) Suggests to small camera users what they don't need to know.
    5) "Full frame" (24x36) is 'a' reference, not 'the' reference.

    I'm a good reader and have a fantastic memory, and don't remember ever reading that in 19 years of digital photography. If I saw it, I undoubtedly dismissed it as useless information. Perhaps you could do a real service to small camera users and explain to them why they should care about "effective aperture" outside of DOF issues. Then we would have something to discuss - something I can take to my friends and discuss.
     
  17. bartjeej

    bartjeej SC Hall of Famer

    Nov 12, 2010
    bart
    Dale: noise (and therefore by extension dynamic range) in digital cameras has, broadly speaking, 2 causes: shot noise and read noise.

    Shot noise is the effect of irregular photon distribution over the sensor's area, read noise is the effect of several factors in the sensor / image pipeline process.

    Shot noise is, always has been, and will forever be determined by the amount of light hitting the sensor - in other words, with a given shutter speed and light level, by the combination of aperture and sensor size - which can be compared across platforms using, you guessed it, equivalent apertures.

    Read noise is a result of electronic processes in the sensor. All the sensor efficiency gains over the years relate to minimizing read noise / maximizing the percentage of photons hitting the sensor that's actually transmitted as (correct) signal.

    As efficiency goes up, the share of read noise in overall noise goes down - which means that the sensor/aperture combination, aka equivalent aperture, is becoming a bigger and bigger determinant of overall noise and dynamic range as the years go by.

    *sigh* and to think I don't even care that much about noise... so long as it's "good enough" for a big print up to ISO 1600 and a small print / black and white print up to ISO 6400, I'm happy.
     
  18. dalethorn

    dalethorn Guest

    Here's the deal - I'm an amateur photographer who has done some simple pro work - portraits etc., but that's about all. I've had Leica and other film cameras, and many many digital cameras, but no DSLR's, which to me are effectively expensive junk.

    As an ordinary photographer, I need to know the effective focal length based on the 135 reference, to know my angle of view, or whatever it's called. That's essential. The DOF issue, mostly for bokeh or whatever reason, is far less essential for me to know, but is still useful in some situations, but then, any camera I have has its limits, so I test the bokeh (if it's important) right there on the live view screen.

    The issue you keep raising is absolutely of NO USE to me, ever, for any reason. Nor is it going to be useful to anyone except a "full frame" user who wants to look down his or her nose at less-than-full-frame users. Now if you have something that is of interest to people like myself and millions of others like me, speak up, otherwise you're telling me nothing, because people already are becoming more aware of sensor size, and they're not going to make a choice of a small fixed-lens camera based on what you're talking about.

    Ordinary people are going to choose their little fixed-lens cameras based on the aesthetics, size, focal length (zoom if not prime), and so on. The secondary thing I mentioned, bokeh, as much as dpreview harps on it, isn't going to make much if any difference in those camera choices, let alone noise issues, UNLESS the actual noise performance gets an unusually bad review from a major camera site.
     
  19. Luke

    Luke Super Moderator

    Nov 11, 2011
    Milwaukee, WI USA
    Luke
    Dale, noise may be useless information for you. But one of the main complaints I hear about small sensor cameras is that they are noisier (and sometimes the "quality' of the noise is not as good).

    as poorly as I grasp as concept, I think it explains why shooting with an f2 lens at the same shutter speed results in a noisier image on a smaller sensor than on a larger one...... is that not the take-away here?

    For myself, I'm fine with modern digital camera noise (for the most part), but saying that noise in a photo is totally irrelevant means we could have all stopped buying digital cameras 5 years ago.

    I'm starting to feel like this thread should be broken into two so that people can post about their wishlist here, and the discussion (which seems to be verging on arguing) about technical stuff get a thread of its' own. I'm on vacation right now and may not get to the job right away.
     
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  20. dalethorn

    dalethorn Guest

    I see that you're misrepresenting everything I've said, which may or may not be deliberate on your part. The point is that serious photographers like myself and my friends are very, very well aware of sensor size and noise issues, and we don't need the "effective aperture" to confuse things.
     
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