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Archive 2012 · Temperature causing softness?
  
 
StarNut
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p.1 #1 · p.1 #1 · Temperature causing softness?


Hi,

I just returned from a frustrating little excursion.

It was very cold outside (8 degrees F), and there was nothing I could do to get my long lens (500/4 IS) to take sharp photos.

It's a very sharp lens, and had shown that just last weekend (last time I was out with it; it was 30 degrees warmer then).

While contemplating the situation on the drive back, it occurred to me that, with telescopes, we have to give the equipment a long time to reach temperature equilibrium, or convection currents in the tube may hurt the image.

So, when I got back home, I let all the equipment reach equilibrium, and, voila, the lens was incredibly sharp, as I expect of it.

Is it a known problem with long (large volume) lenses that it takes them a while to reach thermal equilibrium, and that failure to allow that to happen runs the risk of ruining photos taken while out of equilibrium?

Thanks.



Feb 18, 2012 at 09:15 PM
EB-1
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p.1 #2 · p.1 #2 · Temperature causing softness?


Perhaps. Did you see any condensations? Did you try multiple cameras?

EBH



Feb 18, 2012 at 09:57 PM
StarNut
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p.1 #3 · p.1 #3 · Temperature causing softness?


No condensation; same result on two camera bodies, while shorter lens (24-105) had no issues.


Feb 18, 2012 at 10:02 PM
matanuska
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p.1 #4 · p.1 #4 · Temperature causing softness?


Makes sense. Either air currents in the tube spaces between elements, or distortions in the larges elements as they cool down unevenly. And yes, I've taken my 24-105 (and other short lenses) out in temps as low as -50F and never really noticed any degredation - but I suppose there might be something if I looked really hard.

I don't own a 500mm photo lense, but of course I can definitely see thermal effects in my 102mm APO (800mm FL) as it cools down to equilibrium.



Feb 18, 2012 at 10:32 PM
leftymgp
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p.1 #5 · p.1 #5 · Temperature causing softness?


Well, things will contract in cold weather. Perhaps lenses will go out of calibration when in extreme cold?... Not sure.


Feb 19, 2012 at 12:36 AM
 

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Taoguy
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p.1 #6 · p.1 #6 · Temperature causing softness?


I've taken my 500/4 out in temps much colder than 8F without any problems, after being in very cold weather for several hours I've had my 200-400 zoom much slower but getting sharp photos has not been an issue.
I would try to duplicate using two different bodies if possible. Might not be your lens.

Gerard



Feb 19, 2012 at 12:57 AM
dehowie
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p.1 #7 · p.1 #7 · Temperature causing softness?


Just because it's cold is no guarrantee of freedom from heat distortion.
It is still very prevalent in cold temperatures.
It's around in light or nil wind and shooting over dissimilar surfaces.
The 800 is like a distortion microscope showing every bit and being cold is no guarrantee.
Heat waves are very visible in low temps when viewing over any object hitch can absorb and reflect energy from the sun.
Even on some of the coldest days I have hot on wind is the biggest factor in cold temps.
In hot weather nothing helps.
By far the best protection is shooting after recent rain which flattens the sky for a solid 20minutes after the sun re appears.
Biggest problem with long glass is finding he right conditions to shoot..



Feb 20, 2012 at 01:28 AM
AJay
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p.1 #8 · p.1 #8 · Temperature causing softness?


This is a common occurrence with long telephoto lenses and it is heat refraction. The easiest way to see this is to shoot some video and then watch it during playback. Heat refraction can be caused by turbulent air in/around the lens itself, turbulent air shooting from a car window or other shelter of different temperature or it can be caused by the sun's heat reflecting off of the ground or other surface.

What is interesting is that when looking through your viewfinder it is seldom seen, but looking at live view or watching a video taken afterwards will readily show the problem. The greater the magnification of the lens, the greater the effect will be seen.

There have been many cases where lenses/camera bodies are sent in for repair, when the problem is not with the equipment but due to heat refraction.

Recently I was testing out the Canon 70-200 f/2.8 with a 2x TC inside of my house, focusing on a test pattern. Looking through live view I could see the image shifting on the LCD screen yet autofocus and IS were turned off. The problem was caused by a ceiling fan. As soon as I turned off the ceiling fan, the image on the LCD display stopped moving.

This problem occurs a lot more often than people realize.

Alan
www.iwishicouldfly.com



Feb 20, 2012 at 02:25 AM
StarNut
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p.1 #9 · p.1 #9 · Temperature causing softness?


AJay wrote:
This is a common occurrence with long telephoto lenses and it is heat refraction. The easiest way to see this is to shoot some video and then watch it during playback. Heat refraction can be caused by turbulent air in/around the lens itself, turbulent air shooting from a car window or other shelter of different temperature or it can be caused by the sun's heat reflecting off of the ground or other surface.

What is interesting is that when looking through your viewfinder it is seldom seen, but looking at live view or watching a video taken afterwards will readily show
...Show more

Thanks very much for this!



Feb 20, 2012 at 06:31 PM





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