Understanding Exposures not Understood

Discussion in 'Photography Beginners' Forum' started by RxForB3, Feb 22, 2012.

  1. EchoingWhisper

    EchoingWhisper TPF Noob!

    Joined:
    Aug 12, 2011
    Messages:
    1,553
    Likes Received:
    54
    Location:
    Malaysia
    Can others edit my Photos:
    Photos OK to edit
    No. Because to fill the frame, you'll have to go closer and you'll get less depth of field. And distance scale isn't useful most of the time, it doesn't work on far distances.


     
  2. RxForB3

    RxForB3 No longer a newbie, moving up!

    Joined:
    Feb 10, 2012
    Messages:
    654
    Likes Received:
    77
    Location:
    Yakima, WA
    Can others edit my Photos:
    Photos OK to edit
    Certainly not arguing, so please correct wherever my misconception is. You say I'd have to get closer to fill the frame, but is that necessarily a bad thing? I realize that the closer you get the smaller the depth of field, but if I recall correctly from the dof calculator the hyperfocal distance for the 18mm on a canon would be about 2 feet. Shouldn't that be close enough to fill the frame appropriately even with a small subject such as the gecko?

    Another thought/question. With the 100mm the hyperfocal distance is something like 30 feet at f/22. When using the lens for macro as opposed to say portraits, does the same focus distance apply? Hence the very shallow dof in macro?
     
  3. bazooka

    bazooka No longer a newbie, moving up!

    Joined:
    Dec 28, 2009
    Messages:
    2,293
    Likes Received:
    294
    Location:
    Houston
    Can others edit my Photos:
    Photos OK to edit
    You're observations are why I don't like UE. I don't think he's a good author. The best thing to learn from the book is how to get a good manual exposure, and that small apertures give you large depth of field, and large apertures give you a narrow depth of field. When DoF doesn't matter, choose a middle aperture to get the sharpest image. That pretty much sums up the book.

    And I advise you to check out the charts at Canon EF-S 10-22mm f/3.5-4.5 USM Lens Image Quality for your lens. Compare the sharpness of the aperture at f/22 to f/16, to f/11, to f/8. Notice how massive a difference it (probably) is between f/22 and f/8. It's unlikely you'll need to use f/22 on a crop sensor.

    As far as setting the lens focus distance to 2 feet, if for some reason you would actually need to do that, just focus on something 2 feet away. You don't need a scale to judge distance and it doesn't have to be perfect. Something that might help is to get a DoF calculator on your smart phone if you have one. That way, when you do need to balance between DoF and sharpness, you don't have to guess.
     
  4. RxForB3

    RxForB3 No longer a newbie, moving up!

    Joined:
    Feb 10, 2012
    Messages:
    654
    Likes Received:
    77
    Location:
    Yakima, WA
    Can others edit my Photos:
    Photos OK to edit
    I do have an android smart phone. Do you have a specific dof calculator you recommend?
     
  5. Rephargotohp

    Rephargotohp TPF Noob!

    Joined:
    Nov 2, 2011
    Messages:
    680
    Likes Received:
    148
    Can others edit my Photos:
    Photos NOT OK to edit
    Here's my opinion, Having been a Photographer for over 40 years I do understand the triangle But everyone raved about the book so I bought it. I thought it was a pamphlet and a vehicle for him to show pictures of his hit wife and brag about it. But everyone loves the book so what do I know.

    Here's the thing with your DIF question, When framed equally, ( Equal magnification) Distance to subject and focal length cancel each other out and you will have the same DOF no matter the Focal Length/Distance to subject. So the only thing that will affect DOF is Aperture.

    As far as him recommending f/22. Yes it will yield the greatest DOF but it will also introduce Diffraction within the lens and cause the image to be soft, especially on a cropped sensor camera.

    As far as Hyperfocal distance goes, it's not the cure all to everything. It provides for the maximum DOF for a given Aperture. However it doesn't provide for the sharpest image, especially if you have a singular subject close to the camera. The sharpest point will be the point of focus and everything else is just wintin the field of acceptable focus.

    The best of all worlds were to place your subject at the point of focus and that point being the hyperfocal distance also. So your subject would be the sharpest and then you would have a filed of focus from 1/2 the distance to your subject to infinity.

    The reason that a wide angle lens will appear to have a deeeper DOF, has to do with perspective compression of bringing the background into closer view with a telephoto lens. You can then see that the backgrund is OOF even though the DOF is exactly the same it just to the eye doesn't appear that way.

    You also have to take FOV into account with your Gecko shot. The shot's BG will look entirely different shot with a 18mm at 1' DTS than with a 180mm 10' DTS

    The reason he suggests metering the blue sky is that in essence you are turning your Camare's Reflective meter into a Incident meter and metering the light that lights the scene (skylight) instead of what is reflected off your subject
     
    • Like Like x 2
  6. Rephargotohp

    Rephargotohp TPF Noob!

    Joined:
    Nov 2, 2011
    Messages:
    680
    Likes Received:
    148
    Can others edit my Photos:
    Photos NOT OK to edit
    And if you do focus at something 2' away without a distance scale on the lens, remember that it is from the Sensor plane not the front of the lens
     
  7. RxForB3

    RxForB3 No longer a newbie, moving up!

    Joined:
    Feb 10, 2012
    Messages:
    654
    Likes Received:
    77
    Location:
    Yakima, WA
    Can others edit my Photos:
    Photos OK to edit
    Thanks for the great info! I think at this point I know just enough to confuse myself. Sometimes a little knowledge is a dangerous thing :)
     
  8. FitzTML

    FitzTML TPF Noob!

    Joined:
    Nov 27, 2007
    Messages:
    57
    Likes Received:
    3
    Location:
    Chicago Area, USA
    Can others edit my Photos:
    Photos OK to edit
    I've read the book and learned from it.

    When people talk about the exposure triangle, it does seem like most of the information is copied directly from the film days when ISO was not adjustable. One thing to consider is that (most) cameras operate most efficiently at ISO 100 so the adjustment of the ISO should reflect this (i.e. change shutter speed or aperture before increasing the ISO).

    The triangle boils down to using the shutter speed to freeze or show motion, aperture to narrow or widen the focus plane. ISO and/or additional light is thrown in there.

    One takeaway is that film and sensors don't have the same capabilities as the human eye and are quite limited.
     
  9. gsgary

    gsgary Been spending a lot of time on here!

    Joined:
    Oct 31, 2008
    Messages:
    16,144
    Likes Received:
    2,967
    Location:
    Chesterfield UK
    Can others edit my Photos:
    Photos OK to edit
    Not recommended by me
     
  10. pgriz

    pgriz Been spending a lot of time on here!

    Joined:
    Jul 30, 2010
    Messages:
    6,733
    Likes Received:
    3,212
    Location:
    Canada
    Can others edit my Photos:
    Photos OK to edit
    I'll probably be repeating things people already said, but here goes...

    Prime lenses (those that don’t zoom, but have a single focal length, like 50mm or 135mm, or 200 mm) generally have both the distance scale on them, and a bunch of brackets that mark the effective DOF for that lens at different f/stops. Zoom lenses don’t.

    If you go to the DOF calculator link posted by EchoingWhisper, you will see a nice diagram that shows DOF and hyperfocal distance. Playing around with the calculator, you find some of the following:
    • For a given lens and focal length, DOF increases with aperture (f/22 has more DOF than does f/5.6)
    So, 50mm lens on a Canon 7D, set to an aperture of f/5.6, focused at 20 ft., will have a DOF of about 11 ft. (15’11” on the near end, 27’0” at the far end). At f/22, the near point is at 9’9”, and the far point is at infinity.
    • At the same distance, wider focal lengths give more DOF than do longer focal lengths, EEBE (everything else being equal).
    So a 200mm lens on a Canon 7d, set to an aperture of f/5.6, focused at 20 ft., will had a DOF of about 8” (compared to 11 ft with with 50mm lens set to the same aperture and distance).
    • At the same distance, with the same lens, and with the same aperture, larger sensors give more DOF than do smaller sensors EEBE.
    So if we switched the Canon 7D (which has a sensor with a crop factor of 1.6x) and replace it with a Canon 5D MkII, which has a full-size sensor, the DOF is now almost 19 ft (near side at 14’2”, far side at 33’11”) at 50mm, f/5.6 and 20ft. focusing distance.

    In principle, the plane of focus is exceedingly thin if you have a sensor with infinite resolving power. But in the real world, film media and sensors have limitations, beyond which you just can’t get more detail. That limitation can be expressed as a “circle of confusion” Sensors with large sensing elements have relatively “large” circles of confusion, whereas sensors with very densely packed sensing elements have very small circles of confusion. And this means that something ahead or behind the point of exact focus, will still look in focus if the corresponding out-of-focus circle is less than what the sensor can resolve.

    Now how to use this information?

    Suppose you have a Canon 7D with a 18-55mm zoom lens. You have a scene where you want to capture the flowers at your feet at 6 feet, and you want the horizon to also be in focus. Let’s also say that you decide that the 55mm focal length give you the most pleasing framing. Running the little DOF calculator, you find out that the hyperfocal distance at f/32 is 16’6” and the near point is 8’7”. Not enough. But if you zoom out to 40mm, the hyperfocal distance at f/32 is 8’9”, and the near point is at 4’5”. Perfect! So you find something at 8’9” away from you, set your focus on that, lock the focus, then reframe your picture with the flowers in the foreground and the horizon in the back, and Voila! You got everything in focus that you wanted.

    Now wasn’t that simple?
     
  11. RxForB3

    RxForB3 No longer a newbie, moving up!

    Joined:
    Feb 10, 2012
    Messages:
    654
    Likes Received:
    77
    Location:
    Yakima, WA
    Can others edit my Photos:
    Photos OK to edit
    Gotcha. I was already understanding most of that, but hadn't looked into the circle-of-confusion. Mainly, though, I wasn't understanding how exactly to implement the hyperfocal distance. It's kind of like exposing to something other than your subject (sky for instance). Focus away from the subject, lock it, then recompose. Thanks!
     
  12. CMfromIL

    CMfromIL No longer a newbie, moving up!

    Joined:
    Oct 11, 2011
    Messages:
    710
    Likes Received:
    132
    Location:
    Illinois
    Can others edit my Photos:
    Photos OK to edit


    I had zero experience shooting with the exception to my fully automatic P-N-S camera, and I thought the book was pretty good. Gave me a much better understanding of the basics, and how the 3 pieces play together.

    I wouldn't expect that someone with 40 years experience could really gain much insight from the book. No more than I could from reading a basic drivers ed book on how to drive a car, something that I've been doing now for 25 years.

    It certainly didn't make me an 'expert', but it did make me think a lot more about the camera settings when I go out to take pictures. I think that's where the value is.
     

Share This Page