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  1. #21
    Senior Member
    WayneF's Avatar

    Re: Photography stops

    Quote Originally Posted by Eyelight View Post
    There is a very slight off target in the OP related to the use of EV.

    EV is derived by a calculation that does not consider ISO or lighting . It is used to compare camera settings independent of actual light or film ISO (or digital sensor ISO sensitivity). So, aperture/shutter combinations that yield the same EV will yield the same exposure at the same ISO, but EV does not carry up or down ISO sensitivity. An EV of 15 would only be appropriate for bright sun at ISO 100.
    Bravo! That always seems to be a pretty difficult concept. Not everyone gets it, because it is actually more simple than they want to make it. I have an article at EV - Exposure Value - and Sunny 16. Definition and chart on the subject of EV, which I found hard to write due to the contradictions. Criticisms welcome.

    Meters read EV values, and then ISO settings do produce a different EV reading in same light, only because proper exposure at that ISO then requires other values of camera settings for shutter speed and f/stop. But EV is only about the combination of those camera settings. Specifically, the basic idea is that an EV value is the name of the set of equivalent exposures of all the combinations on that one EV row.


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    Last edited by WayneF; 12-25-2014 at 03:41 AM.



  2. #22
    Senior Member
    Challenge Team
    Eyelight's Avatar

    Re: Photography stops

    Quote Originally Posted by Vincent View Post
    A practical application of this.
    I have the impression that the Sony A7 II is of no use for me, I have to stay with my idea to get better ISO performance, let us reason in stops.

    Sony A7 II
    IBIS 4.5 stops improvement on the shutter speed.
    ISO 6400 (DXO Mark Dynamic Range EV score of 8 for the original A7)
    24 Mpix

    better ISO: Sony A7s
    ISO 51200 (that is 3 stops better then the A7 II)
    12 Mpix
    ========================
    So in overall the A7 II is better due to better resolution and system that makes you gain more stops (1.5 more).
    If I want to take a picture with a 50mm I can do 1/2s schutter time hand held normally with good results, with a bit of technique even slower.

    Now the A7s has only 12 Mpix, but the strength is that it shows good 12 Mpix at high ISO.

    Take a scene which needs flash: 5EV Night home interiors, average light. School or church auditoriums. Subjects lit by campfires or bonfires.
    Can you do something without flash with this new technology?
    We start from daylight 15EV 1/1000s ISO 200 f5.6.
    There is gain of 10 EV needed, we go down to f2.8 so 8EV left to gain.

    A7 II: 1/3s ISO 200 f2.8 would be possible and give the picture with a 50mm;
    clearly I might choose f5.6 ISO 6400 1/30 s to be able to handle a little movement and have more DOF.

    A7s: 1/250s ISO 12800 f2.8 is well possible according to most reports
    Clearly I might want to choose: ISO 51200 f5.6 1/250s for a high shutter speed with more DOF.

    So now it depends what you want to do.
    The A7 II is good for a choir concert ,if their song is not too energetic.
    I`ll probably be in a ruin looking at a birds nest with a telephoto and for me the A7 II will be useless at 1/30s, obviously a Df or D3s will do better for me, since the shutter speed is higher due to the stops gained in ISO and not in slower shutter speed.
    I needed a cognitive exercise, so I waded thru the reasoning. So, what you arrived at, is the gain in stops of higher ISO allowing shorter shutter speeds (freezing subject motion) is more important to your photography than the gain in stops of better image stabilization allowing longer shutter speeds (with less camera motion). Makes sense.
    Last edited by Eyelight; 12-26-2014 at 03:27 PM. Reason: clarified less camera motion
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  3. #23
    Senior Member
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    Eyelight's Avatar

    Re: Photography stops

    Quote Originally Posted by Stoshowicz View Post
    Well Im meaning absolute in terms of , ummm, the camera already calculates how much light is coming into a sensor based on a voltage accumulated over a period of time, knowing aperture and ISO,,
    Then it calculates whether that would be over or under exposed at the settings you chose.
    It seems that it should be able instead to calculate the brightness of the scene and just tell me THAT- instead of changing the output 'relative value' with each click of aperture speed or change of ISO. I could then do a sweep of my circumstance , get a basic idea of how bright the scene is irrespective of my settings , and then I could go right to whatever settings I like to use, I wouldnt have to do clicks up and down from a floating exposure value. Im in accord with the old school guys, almost never use automated exposures and half the time never even consult the meter.

    The camera appears to have the data , they just don't program it to inform in this manner.
    The camera meter does it, but displays the EV graphically on the exposure indicator using the current settings as a reference.

    If we set manually, for instance, 1/100 @ f/16 ( or any other EV15 combination), then we have essentially zeroed the exposure indicator at EV15. If the meter thinks the light requires EV14 settings then it will show us on the exposure indicator -1 stop and if EV16, then show us +1 stop.

    We can use the meter to sweep a scene by watching the exposure indicator with spot metering or let the camera do the sweeping with matrix. Either way, the exposure indicator is using our EV15 setting to tell us or point us at the EV it is reading. And if we are within the stops marked on the exposure indicator, the meter is providing an EV number, just in a graphical way.
    Last edited by Eyelight; 12-26-2014 at 04:24 PM. Reason: typo
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  4. #24
    Senior Member
    Stoshowicz's Avatar

    Re: Photography stops

    Quote Originally Posted by Eyelight View Post
    The camera meter does it, but displays the EV graphically on the exposure indicator using the current settings as a reference.

    If we set manually, for instance, 1/100 @ f/16 ( or any other EV15 combination), then we have essentially zeroed the exposure indicator at EV15. If the meter thinks the light requires EV14 settings then it will show us on the exposure indicator -1 stop and if EV16, then show us +1 stop.

    We can use the meter to sweep a scene by watching the exposure indicator with spot metering or let the camera do the sweeping with matrix. Either way, the exposure indicator is using our EV15 setting to tell us or point us at the EV it is reading. And if we are within the stops marked on the exposure indicator, the meter is providing an EV number, just in a graphical way.
    Yes, thats true , but the 'graphical way' they choose, is relative to the settings and gear I'm using rather than to a constant zero. Each time you change a lens , add a TC, change your 'working ISO' youve got to do it all over again. If I compare my EXIF data to someone with a smaller objective lens, etc, the settings I used wont match theirs, unless Im using the same gear and shooting the same scene at the same time, so they cant imitate my settings and get the same exposure , if I wanted to back-calculate the actual 'brightness' of the scene I cant do it , because its a 'floating' standard relative to the situation at the sensor, rather than relative to the light coming off the target I am shooting.

  5. #25
    Senior Member
    Challenge Team
    Eyelight's Avatar

    Re: Photography stops

    Quote Originally Posted by Stoshowicz View Post
    Yes, thats true , but the 'graphical way' they choose, is relative to the settings and gear I'm using rather than to a constant zero. Each time you change a lens , add a TC, change your 'working ISO' youve got to do it all over again. If I compare my EXIF data to someone with a smaller objective lens, etc, the settings I used wont match theirs, unless Im using the same gear and shooting the same scene at the same time, so they cant imitate my settings and get the same exposure , if I wanted to back-calculate the actual 'brightness' of the scene I cant do it , because its a 'floating' standard relative to the situation at the sensor, rather than relative to the light coming off the target I am shooting.
    Maybe it''s too early in my day, but I can't follow your thoughts. So, not sure this is on the same page.

    If you look at a well exposed shot and know the EXIF (aperture, shutter speed & ISO), then another number is only going to tell you the same thing in a different language.

    Regardless of camera and lens, if the same trinity of settings is used, the exposure will be the same. The image may be different depending on camera and lens. But the same aperture, shutter speed and ISO will always be the same exposure and, once the right exposure has been achieved, better than any other info we could add.
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  6. #26
    Senior Member
    Stoshowicz's Avatar

    Re: Photography stops

    Quote Originally Posted by Eyelight View Post
    Maybe it''s too early in my day, but I can't follow your thoughts. So, not sure this is on the same page.

    If you look at a well exposed shot and know the EXIF (aperture, shutter speed & ISO), then another number is only going to tell you the same thing in a different language.

    Regardless of camera and lens, if the same trinity of settings is used, the exposure will be the same. The image may be different depending on camera and lens. But the same aperture, shutter speed and ISO will always be the same exposure and, once the right exposure has been achieved, better than any other info we could add.
    If I use a faster lens will the exposure be the same?

  7. #27
    Senior Member
    Challenge Team
    Eyelight's Avatar

    Re: Photography stops

    Quote Originally Posted by Stoshowicz View Post
    If I use a faster lens will the exposure be the same?
    If the faster lens is set at the same aperture, yes, the exposure will be the same. The term faster lens just means the lens has a larger maximum aperture, but any two lenses set at the same aperture will allow the same amount of light to pass.

    Edited to add: Clarifying, the aperture itself will be a different size depending on focal length. That's where f/stops come into play. The same f/stop on any lens will produce the same amount of light hitting the sensor at the same interval of shutter open.
    Last edited by Eyelight; 12-29-2014 at 02:59 PM.
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  8. #28
    Senior Member
    Stoshowicz's Avatar

    Re: Photography stops

    Quote Originally Posted by Eyelight View Post
    If the faster lens is set at the same aperture, yes, the exposure will be the same. The term faster lens just means the lens has a larger maximum aperture, but any two lenses set at the same aperture will allow the same amount of light to pass.

    Edited to add: Clarifying, the aperture itself will be a different size depending on focal length. That's where f/stops come into play. The same f/stop on any lens will produce the same amount of light hitting the sensor at the same interval of shutter open.
    Faster lenses , often have larger objectives,Is the light gathering potential is greater with a larger objective?

  9. #29
    Senior Member
    WayneF's Avatar

    Re: Photography stops

    Quote Originally Posted by Stoshowicz View Post
    Faster lenses , often have larger objectives,Is the light gathering potential is greater with a larger objective?
    Only if you open it wider to use it (potential, not actual in all cases).

    f/stop number = focal length / aperture diameter (effective diameter, viewed through magnification of front elements).

    The sole purpose of inventing f/stop is that f/8 is f/8 in any lens. A 200 mm lens will have an aperture area 4x larger than a 50 mm lens, so that f/8 will be f/8 in both. A faster lens may open wider, say to f/1.4, but when at f/8, its diameter is stopped down, so that is NOT f/1.4 then, it is a f/8 lens.

    We could discuss minor variations, T-stops and transmission of lenses with poor coatings, or 15 lens elements, but the the big idea is that f/4 is f/4.

  10. #30
    Senior Member
    Challenge Team
    Eyelight's Avatar

    Re: Photography stops

    Quote Originally Posted by Stoshowicz View Post
    Faster lenses , often have larger objectives,Is the light gathering potential is greater with a larger objective?
    Faster lenses often have larger objectives in order to pass light thru the larger maximum aperture. As the aperture is stopped down, less of the objective lens is used. So, f/8 passes the same amount of light thru a 1.8 lens as it does thru a 5.6 lens.
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