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I've got a Panasonic Lumix FZ72: a 20-1200mm superzoom. It's pretty good, and has pretty decent image quality for the price.

Unfortunately, I've noticed that if I take any pictures past roughly 400mm of anything more than a kilometer away, the images get "mushy". I doubt that it's the lens, given that I've taken fairly decent pictures up to 1200mm on the same camera. That must mean that I'm seeing atmospheric effects. But I'm seeing this "mushy effect" at only 400mm in a town with pretty clean air. So what gives?

Am I seeing atmospheric effects? When can I generally expect to see them?

This is an image taken at 402mm, about 1.7km from the subject. If you zoom in, you can see that the image is slightly "mushy".

Another image I took at 402mm, no atmospheric effects, subject about a meter from the camera.

An image I took at 145mm, again no atmospheric effects visible as the flowers were right in front of the camera.

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    Depends so much on local conditions. If you're shooting across a black tarmac road on a sunny day, expect atmospheric effects at just about any focal length. If you're shooting at the top of a big mountain on a still day, expect very different results. – Philip Kendall May 28 '17 at 16:54
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    "Mushy" is not a very exact term. It would be better if you put an example. – Rafael May 28 '17 at 18:23
  • An image is worth thousand words... please, supply an example. – roetnig May 29 '17 at 6:19
  • @Rafael and roetnig, I've edited the question to include the image in question (402mm), another image at 402mm and 1m distance to subject, and another image at 145mm. – Owen Versteeg May 29 '17 at 8:06
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    Owen, thanks for providing pictures. Would you mind editing your question and actually insert them into your question, rather than linking to them? Links to externally-hosted images tend to rot over time, causing confusion for future readers who can't see the images being talked about. Thanks! – scottbb May 29 '17 at 13:47
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Atmospheric effects aren't caused by using a particular focal length. They are caused by how much air is between the camera and the subject, by the uniformity or lack of uniformity of the temperature and density of that air, the stillness or turbulence of the air, and the amount and types of particulates suspended in that air.

We notice atmospheric effects more when using longer focal lengths only because we tend to shoot at longer subject distances when using those focal lengths and because the narrower angle of view we get with such focal lengths increases the magnification of any atmospheric effects in that narrower field of view when we view the resulting images at a particular display size.

Your first example shows a near textbook case of haze and other particulates in the air through which you are shooting. The result is that the parts of the image that are further from the camera show a loss of contrast as well as loss of detail.

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    ah, should have asked "roughly at what distances will I start seeing atmospheric effects?" Should I edit this question or make a new one? – Owen Versteeg May 28 '17 at 20:44
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    It's still way too variable based on the conditions. In cool, dry, stable air you can see for a hundred miles with very little effect. In other conditions you can't see across the street. – Michael C May 28 '17 at 20:51
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    @OwenVersteeg, the only concrete answer is the upper bound: even under ideal conditions, you can't see more than about 200 miles/300 km. – Mark May 29 '17 at 1:28
  • @Mark, so how far away are all of the stars in the sky? – Michael C May 29 '17 at 3:19
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    @MichaelClark, about five miles. Air thins out rapidly as your altitude increases, so when looking up, you're seeing starlight that's traveled through an amount of air equivalent to five miles of sea-level atmosphere. – Mark May 29 '17 at 3:27
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Without looking into the details here, it sounds like you are seeing blurring coming from the camera diffraction limit hitting in.

Given perfect optics, the diffraction limit dictates the smallest focal spot the lens can generate. Roughly speaking for visible light, the blur diameter is (a bit more than) the camera lens working F-number in micrometers. (Search Airy disk diameter for details.) A superzoom lens can modify the focal length (f) on the fly, but I very much doubt it could keep increasing the camera aperture (D) at the same rate. F/# = f/D, thus as you focal length f keeps increasing, so does the f-number.

The lens zoom ratio is 1200 / 20 = 60X. If D stays roughly constant, you would get 60 times more blurring just from diffraction in the far end of the zoom range.

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    Keep in mind that the 'D' in f=FL/D is the diameter of the entrance pupil, not the absolute aperture diaphragm size. Diffraction, on the other hand, is determined by the physical size and shape of the actual diaphragm. As most lenses zoom the entrance pupil is also enlarged by the increased magnification between the diaphragm and the front of the lens. Constant aperture zoom lenses maintain the ratio as they zome, but even lenses that aren't constant aperture usually come fairly close. Otherwise an 18-55mm that is f/3.5 at 18mm would be f/11at 55mm. – Michael C May 29 '17 at 8:22
  • That's demonstrably false for this situation. – Carl Witthoft May 30 '17 at 11:35

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