atmospheric distortion - moon/sun horizon shots

Discussion in 'Nature' started by 15sunrises, Dec 10, 2008.

  1. I've been trying to get some good shots of the moon/sun rising and setting, but find that atmospheric distortion is a major problem in these situations. Meanwhile, I see a lot of images online of the moon/sun which seem to have avoided this problem somehow. I'm wondering what factors contribute to the amount of distortion, and what I can do to help avoid it as much as possible. I'm thinking that 2 factors may help:
    #1 - getting out of the city, I would think that smog/pollution contribute to this quite a bit
    #2 - altitude - would it be safe to say that at higher altitudes, this phenomenon is less visible?
    I appreciate any help that people can provide with this. After searching online, I found a lot of info about wavelengths, etc. but not exactly any useful information on how to deal with this problem as a photographer who wants to avoid it (rather than photograph the distortions).
    thanks
     
  2. There is little way to deal with it.
    The problem is the amount of air between you and the horizon and how turbulent it is.
    The city does add turbulence, and hence may make it less likely to observe a little distorted sunset, but there is always some distortion at the true horizon. Increasing you own altitude does not change the situation for better, it actually makes it worse. If you're on a mountain then there is even more air since the horizon is farther away. So, to best avoid the distortion not you yourself, but the horizon must be higher; like looking towards hills with you yourself standing in a valley.
    Cheers, Rivi
     
  3. In general it's the atmosphere, especially in and around cities, and the best way is to get away from it is distance or elevation. Secondly, have a tripod with a good adjustable head to track the movement. And lastly, preferably, the longer the lens the better. Your and others mileage may vary.
     
  4. There's is also a technique employed by astronomers called "Lucky imaging" to fight turbulence. The principle is simple: Shoot as quickly as possible and keep only those with the least distortion. It can as well be used for sunsets .
     
  5. Hmm, so how can I actually get closer to the horizon then?
    ;)
     
  6. Well, the quantity called "airmass" goes with something like 1/cos(altitude). It's one in the zenith, and about infinity (not exactly, because the earth isn't flat) at the horizon. But you see, every degree the actual horizon is higher than the "true" one (that one being at 90 degree form the zenith) helps a lot. See the picture in the Wiki article for details, but be aware that in particular the interpolation formulae with decreasing airmass at low altitudes are not valid anymore at these low altitudes. At high elevations, the actual horizon is even below the "true" one. If you have the opportunity to see the sun setting into the sea from a high mountain you even see the sun shining "upwards" quite clearly when watching the shadows.
     
  7. Why not enjoy the distortion and take advantage of it photographically?
    There are photographers that try to find this distortion.
    Please see Atmospheric Optics website and do a search for distorted sunrises to see some great examples and scientific descriptions.
    http://www.atoptics.co.uk/
     
  8. SCL

    SCL

    Assuming you weren't being facetious when you said "Hmm, so how can I actually get closer to the horizon then?", the answer is that you have to bring the horizon to you...essentially be below the horizon, like in a valley with mountains...the horizon is then closer from a photographic standpoint. If you are above the surrounding area, the horizon extends further. That's why on old sailing ships (and modern ships), the crow's nest or bridge is higher than most other points on the ship...so that one can see further, and extend the horizon.
     
  9. Getting out of the city is scary to some people. I heard of one person who couldn't stand being in the great outdoors because people were breathing air there "that they couldn't even see".
     
  10. Atmospheric refraction causes the Sun's or Moon's altitude to appear greater than it is. Near the horizon, the bottom of the body is refracted more than the top, resulting in vertical compression. In most cases, there isn't much you can do about it, though refraction is slightly less at greater elevations because the air isn't as dense. Turbulence, as such, doesn't have much effect on refraction, but it can cause a shimmering appearance, which can cause some softness, especially at longer exposure times. In my experience, getting away from a city usually helps reduce this.
    Refraction decreases considerably as the Sun or Moon moves above the horizon, but in many cases, so does the photographic interest. But that really depends on the location. For example, shooting the Moon setting over many locations in California's Sierra Nevada gives quite a different result from shooting the Moon rising over San Francisco. In the former case, there is little atmospheric distortion, and the Moon is usually much whiter and sharper. This is the result of several factors:
    1. The air around the Sierra usually has far less pollution.
    2. The base elevation around many locations on the east side of the Sierra (say about 4500 ft) is greater so the air is less dense, and there is less refraction.
    3. The altitude of the distant mountains from many camera locations is much greater (say, for example, 10°), so the light passes through less of the atmosphere than it might in SF, where the hills to the east are typically around 1° altitude.
    So it's usually possible to get a much whiter, rounder, sharper Moon over distant mountains than in most urban locations. But there can be downsides, as well. Because the light passes through less atmosphere, the attenuation is less, and the Moon–foreground contrast can be tougher to manage, especially if you're shooting at or before sunrise.

    To my mind, atmospheric distortion is part of the appeal, and it's the way the Sun or Moon actually appear. Refraction at the horizon is highly dependent on atmospheric conditions, especially temperature, so almost no two rises or sets are the same. This, again, is part of Sun and Moon rise and set photography.

    Although airmass and refraction both result from the passage of light through the atmosphere, they aren't quite the same thing, and the formulas for airmass can't be used to calculate refraction. There are formulas for both airmass and refraction that are reasonably accurate at the horizon, but they assume a standard temperature profile that isn't always met in practice (and the true values are almost always unavailable), so they're best treated as approximate.

    Incidentally, the airmass is given by 1/sin(altitude) = 1/cos(zenith angle). But this formula is only good down to about 10° altitude, so it's often not of much use when photographing the Sun or Moon as part of a landscape. And the airmass relates more to the brightness of the Sun or Moon than to the refraction.

    Again, since it's usually tough to fight 'em, why not join 'em and enjoy the variety that accompanies every rise and set?
     
  11. They're both taken "uphill", towards the ridge of a hill. So, get out your favourite planetarium-prgram to find out what direction sun/moon rise/set will be, grab a compass and find a spot with hill-sight towards east/west.
     
  12. Ran into the same thing and told my wife that the effect simply adds character to the shot.
     

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