20 thoughts on “Balls

  1. Wow, you danced a Tango! I’m so impressed.

    Furthermore, there is photographic evidence, so “I don’t dance Tango” will never work as an excuse again. Although I might let you off occasionally, because I’m just nice like that 🙂

    1. I was badgered into it. I just did my Robin and Glennis beginners’ special all the way around the room, but my partner didn’t seem to mind.

      1. Clive is always teaching tango (for suitable values of “always”), it’s just I never get the routine down well enough to use it outside the lesson, so I generally don’t do it because what I do know is boring. I used to have the same problem with foxtrot, but that’s OK now.

  2. Subject: DOF+freezing motion
    Canon DSLRs have pretty good high-ISO performance. Having taken many low-light candids I can say it helps a lot.

  3. Subject: Photography theory…
    If by depth of field, you mean lack of it, then you have to have a lens with a large aperture. The next bit’s long and technical, sorry! But it does a contain a bad bit of ASCII-art.

    When a lens is focused, all light from a point on the subject which comes through the aperture of the lens gets focused onto a single point on the sensor. Since there are light rays passing through the whole aperture, they are not exactly parallel, so a displacement from the focus point (actually a plane) along the axis of the lens will result in a corresponding change of position on the sensor. Since the direction of this change is different depending which bit of the lens the light went through, points displaced from the focal plane are out of focus.

    Now with a large aperture, (or if the subject is nearer) the variation in angle at the subject is greater, so it takes a smaller change in distance to become significantly out of focus. So the only way to have a shallow depth of field is to have a large aperture, or photograph something from really close up! As a reference, my favourite low-light lens is a 50mm f/1.4, which means the aperture is around 34mm. Clearly no compact camera can have an aperture approaching this size.

    Here’s a diagram, where the v marks the focal point:

       S   | |__
       E  /|L|  ------____  v  _____-------
       N . |E|            -----___
       S  |N|     _____--        -------_____
       O   |S|----
       R   | |
       

    Low light is the same solution; a large aperture is a must. Hence all pictures taken in low light will have a shallow depth of field. There’s not much difference in the quality of sensor between compact and SLR cameras, it’s nearly all in the lenses.

    Also, the more you zoom in, the smaller the area you are collecting light from, so the larger aperture you need. For this reason, aperture sizes are actually given as the focal length (which corresponds to the amount of zoom) divided by the physical aperture diameter. So an f/2 lens has an aperture of half its focal length. A lens of any focal length will let in the same amount of light if it has the same f-number. Quite pleasingly, if the image is cropped to the same size (by standing further away with long focal lengths) the depth of field also depends only on the f-number.

    I hope someone understands some of that.

    1. Subject: Re: Photography theory…
      I think I got some of it. I was wondering about how he took stuff like this, where people towards the back are in focus, but (from memory) there wasn’t a lot of light. If the EXIF stuff is right, he had a 4.25mm aperture, so maybe there was more light around than I thought.

      I must get around to understanding all these photographic terms at some point.

      1. Subject: Re: Photography theory…
        Remember, what determines the amount of light hitting the sensor is the ratio of focal length to aperture size. So although the physical aperture is small, it’s still f/4, which is what matters. This is because with a short focal length you’re collecting light from more different directions. So the large-ish f-number gives you enough light (I think f-numbers get larger towards 0, not sure!). The large depth of field is due to the small absolute aperture size (or large subject, depending on how you want to think about it.)

        It’s still impressive; the 20D really is very good in low light. And in a little while it will be mine 🙂 I’m excited.

      2. Subject: Re: Photography theory…
        The alternative to a wide aperture or slow shutter is of course to underexpose and then adjust the exposure in software. Taken to extremes this results in posterization but given that you’re collapsing (typically) up to 12 bits into 8, you can actually get away with quite a bit. I don’t know if that’s what the photographer did in that case though; AV mode and the lack of any exposure compensation suggests not.

        1. Subject: Re: Photography theory…
          Given that he’s already shooting at ISO 1600, any more gain is likely to result in an unacceptable amount of noise. If more gain could reasonably be achieved, the 20D would have a higher ISO setting than 1600. (Actually I think there’s a custom option for 3200, but it would be unacceptably noisy for my liking.) Comparing the EXIF data with some of the other images, though, I would guess the camera did meter a bit high and Deian increased the exposure a bit in software.

      3. Subject: Re: Photography theory…
        If I remember correctly, I used the flash for that picture. I figured that the 17-40/4.0 zoom is 2 stops and a third slower than the 1.8 primes, so the speed would have been unacceptable if using only available light. 1/100 is a bit slow for moving objects, but I wanted to catch some ambient light too, and I was hoping that the flash would be sufficient to freeze the motion. I bounced the flash from the ceiling, thus the shadows on the shirts and behind the dancers are as if the light is coming from above, which makes it look as if available light was used.

        It seems that when I am using the flash the EXIF parsing code on my website reports “Flash: undefined”, and if I am not using it, it reports “Flash: 16”. Weird.

      1. Clare’s only in two of the three shots…

        Clare has a blink reflex for the camera flash, so I have a tendency to photograph her without a flash…

Leave a Reply

Your email address will not be published. Required fields are marked *