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FORUMS Photography Talk by Genre Bird Talk
Thread started 10 May 2017 (Wednesday) 04:22
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Heat shimmer using superteles vs lighter zooms

 
Bjarne ­ Hemmingsen
Member
Bjarne Hemmingsen's Avatar
Joined Mar 2017
Skanderborg, Denmark
May 10, 2017 04:22 |  #1

In my part of the world most photographers may deal with Heat shimmer from the ground on warm days and it is nearly impossible to get a sharp shot on long distance with a supertele, but....

1.: Why does it seems to be nearly as bad on short distances near the focus limit? (Can the heat Affect the gear and micro-adjustments, so it is not the heat shimmer from ground I have to blame for ALL the blur on the photos...? ...or are there shimmer inside the lens, when it is warmed up?)

2.: Why does it seems to have a lighter effect on lighter lenses?

It is a general issue and I know about the effect from Heat shimmer, but canĀ“t figure out the 2 questions! Last week we were 8 photographers with different gear but same experiences, so it is not my skills or adjustments I ask for advice about. (I believe that in any case, but of course, I am open to suggestions...)

Anyone who have a Technical explanation or which may refer to articles about the subject?




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MalVeauX
"Looks rough and well used"
MalVeauX's Avatar
Joined Feb 2013
Florida
Post has been edited 6 months ago by MalVeauX.
May 10, 2017 08:16 |  #2

Heya,

1. At close distance, you're at higher magnification, and turbulence will greatly effect that. Yes, the heat turbulence is to blame. The air within the lens can heat up too, and it does matter a little, but ultimately shooting through turbulence, at high magnification, will result in blur.

2. Less magnification, less apparent blur.

The heat turbulence on the ground is both reflecting and radiating heat. Just like above a hot road. Just like above a fire. And essentially similar enough to the atmospheric seeing we shoot through. The turbulence will be the limiter when trying to capture an image through it, and the worse the turbulence, the more of a limit it becomes, and using higher and higher magnification through that turbulence won't work. It has to do with sampling limits. At great distance and lower magnification, the turbulence is less apparent, due to it's movement being represented as a lower portion or the arc-seconds making up your FOV. But at higher magnification, up close, the same movement is making up more of the FOV, so apparent blur is increased.

When you're shooting over heat turbulence or through it, it will always basically be the limiting factor to a sharp image. When I notice it when shooting birds for example, I don't bother taking the shot and move on.

To learn more, read about:

Atmospheric turbulence, specifically the "seeing" and how photographers image through it and what it limits
Sampling based on resolution (this involves aperture size and pixel size)
FOV and object movement in degrees, broken down into arc-seconds and why things are described in arc-seconds (such as "seeing") and how this is a limit and a major factor of "blur" (this applies to why a bird will blur at close range due to faster apparent movement than long range with slower apparent movement; but applies here too)

Very best,


My Flickr (external link) :: My Astrobin (external link)

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Bjarne ­ Hemmingsen
THREAD ­ STARTER
Member
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Joined Mar 2017
Skanderborg, Denmark
May 11, 2017 06:05 |  #3

MalVeauX wrote in post #18350821 (external link)
Heya,

1. At close distance, you're at higher magnification, and turbulence will greatly effect that. Yes, the heat turbulence is to blame. The air within the lens can heat up too, and it does matter a little, but ultimately shooting through turbulence, at high magnification, will result in blur.

2. Less magnification, less apparent blur.

The heat turbulence on the ground is both reflecting and radiating heat. Just like above a hot road. Just like above a fire. And essentially similar enough to the atmospheric seeing we shoot through. The turbulence will be the limiter when trying to capture an image through it, and the worse the turbulence, the more of a limit it becomes, and using higher and higher magnification through that turbulence won't work. It has to do with sampling limits. At great distance and lower magnification, the turbulence is less apparent, due to it's movement being represented as a lower portion or the arc-seconds making up your FOV. But at higher magnification, up close, the same movement is making up more of the FOV, so apparent blur is increased.

When you're shooting over heat turbulence or through it, it will always basically be the limiting factor to a sharp image. When I notice it when shooting birds for example, I don't bother taking the shot and move on.

To learn more, read about:

Atmospheric turbulence, specifically the "seeing" and how photographers image through it and what it limits
Sampling based on resolution (this involves aperture size and pixel size)
FOV and object movement in degrees, broken down into arc-seconds and why things are described in arc-seconds (such as "seeing") and how this is a limit and a major factor of "blur" (this applies to why a bird will blur at close range due to faster apparent movement than long range with slower apparent movement; but applies here too)

Very best,

Thank you for a logical and (for me nearly) understandable explanation...;o))




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SleepingMoose
Hatchling
3 posts
Joined May 2017
Amsterdam, the Netherlands
May 17, 2017 17:29 as a reply to MalVeauX's post |  #4

With spotting scopes I notice a large amount of blur after setting up the scope in full sunlight. But half an hour later the view is better. It seems that the equipment and the air/gas within it need to have the same temperature.

This is just field experience. And scopes and binos are filled with gas, cameras with air, it may make a difference. Have not tested it with my Canon 100-400 II yet, but even here it's getting warmer :-)




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Heat shimmer using superteles vs lighter zooms
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