EF600/4 lens hood image distortion

After beating myself over the head for years trying to find the cause of occasional severe image distortion in my bird photography setup, I've discovered an unlikely contributor: that great, big, 8" long, lens hood that comes with the EF600/4LIS (ET-160) and other versions going back to the FD model.

I do most of my bird photography under clouds or in shade rather than full sun because I've always had some trouble with heat distortion with images in full sun (effective focal length 1200mm). I've always (more than 20 years) attributed it to external thermal currents, now I know that *some* soft images are due to heating of the lens hood itself. With the lens hood in direct sun on a cool day (70 degrees F or less) it becomes hot enough to be uncomfortable to touch in minutes and the bigger the difference between ambient temperature and hood temperature, the worse the distortion is.

I notice that the Nikon long black lenses don't have hoods quite as long as Canon's and at least some models have an adjustable sliding length feature which may help with this problem.

By comparing image frames, videos and magnified LiveViews at 100% with and without the solar heated hood, I can easily see the effect of the heated air inside the hood. At an "actual pixel" viewing level, critical focus, or not, is obvious.

I spent a little time trying to figure out how to make a short lens hood that would not trap heated air so well and would work for me in the way I handle the lens and R5 with the usual 2x tele, when I accidentally found that Canon makes a short, 4", version of the hood, exactly what I thought would help and wouldn't expose that vulnerable front glass element to handling and weather.

I've been a Canon 600mm lens user for about 35 years and thought I knew it's products for telephoto lenses reasonably well, but the existence of this alternate lens hood was almost a shock and what else could it be for except to fix this problem I've been having for so long? And I've never seen it mentioned in any reviews or other publications. In fact, thermal distortion of images at high camera magnification is rather overlooked or barely mentioned, too.

By the way, those cool-looking dark camo adhesive fabrics have got to make this worse by adsorbing more solar energy than the basic white color. And, also BTW, you won't see this as a problem if you're not into making highly cropped images and/or largish prints - you can get away with a lot of image faults in web publishing.

https://petapixel.com …os-taken-in-cold-weather/

Thanks for that link.

The article shows the effect at it's extreme of temperature differences, however, what I'm seeing has nothing to do with cold weather, my problems have been on warm days as well as cool ones.

The author gets it right that the difference in temperature (delta T) is what causes the atmospheric waves and the bigger delta T is, the worse the effect. Since neither he nor I have that temperature measurement, we can't be too sure which way is worse. Approximately, in my case, the ambient temp was in the 70s F and the part of the hood I touched was about 105 F (by feel, I often test water for baking bread by feel and have a fair idea of how hot that is.) I also know from other sources that 125 F is too hot to touch for more than a few seconds, so that's my ballpark.

Also, there's confusion in the discussion between thermal distortion vs lens fogging.

It's really unfortunate that this effect isn't covered in detail in the manufacturer's docs nor in any magazine article I've ever seen. Certainly, the problem goes back nearly as far as I am old and should be in the arena of common knowledge.

I'm hoping that the short version of the lens hood will reduce the effect substantially while still protecting the front element and, if not, I'm contemplating drilling holes in it to vent the warm air quickly.

FrankKolwicz wrote in post #19434076
Thanks for that link.

The article shows the effect at it's extreme of temperature differences, however, what I'm seeing has nothing to do with cold weather, my problems have been on warm days as well as cool ones.

The author gets it right that the difference in temperature (delta T) is what causes the atmospheric waves and the bigger delta T is, the worse the effect. Since neither he nor I have that temperature measurement, we can't be too sure which way is worse. Approximately, in my case, the ambient temp was in the 70s F and the part of the hood I touched was about 105 F (by feel, I often test water for baking bread by feel and have a fair idea of how hot that is.) I also know from other sources that 125 F is too hot to touch for more than a few seconds, so that's my ballpark.

Also, there's confusion in the discussion between thermal distortion vs lens fogging.

It's really unfortunate that this effect isn't covered in detail in the manufacturer's docs nor in any magazine article I've ever seen. Certainly, the problem goes back nearly as far as I am old and should be in the arena of common knowledge.

I'm hoping that the short version of the lens hood will reduce the effect substantially while still protecting the front element and, if not, I'm contemplating drilling holes in it to vent the warm air quickly.

That article was just weird. Such extreme, sudden changes in environment are going to cause problems, hood or no hood.
Regarding hood 'covers', I think a light coloured fabric over neoprene would be a benefit.
It would be easy to test. Leave hood in sun for 15 minutes with such a cover, then remove cover and I'm sure temperature of hood will quickly rise.
I'll do this test when I get a chance, though with a camo coloured neoprene cover as that's what I have.

I often use a small towel to drape over long lens and body on hot days with no clouds. It's obvious just touching the body how much cooler it is.

It looks like a clear sunny, but cool, 70F high for the day, so I've gotten my pyrometer out and I'll put the hood out in the sun and take some temps. Afterward, if I have time, I'll make some test images.

I did a little testing yesterday, but there was haze and high thin clouds, so the hood wasn't as hot as previously noted.

I am not surprised at this. Most likely thermal effects around the lens can cause a reduction in sharpness.

I had planned to do a comparison with a white and black lens hood in the sun but never got around to it. Maybe one day...

I use a 3D printed lens hood on my Canon 500mm because the Canon hood is just too long. it does not seem to retain much heat from the sun, even though it's black.

When I laid the hood in the sun at 70F ambient for just a couple of minutes the hottest area got to 120F inside and outside.

I also remembered that there were often times when the first few minutes of use, after poking the camera out of the window of the relatively cool car on a hot day caused distortion problems that went away a little later.

I now use the short hood or none whenever possible.

Simple solution: Move to Sweden.
Bring warm underwear and gloves.

apersson850 wrote in post #19436861
Simple solution: Move to Sweden.
Bring warm underwear and gloves.

I was in Sweden, for a few hours. It was nice there (in the summer).

It is not the temperature, but the temperature difference, that causes distortion.

FrankKolwicz wrote in post #19434076
Thanks for that link.

The article shows the effect at it's extreme of temperature differences, however, what I'm seeing has nothing to do with cold weather, my problems have been on warm days as well as cool ones.

The author gets it right that the difference in temperature (delta T) is what causes the atmospheric waves and the bigger delta T is, the worse the effect. Since neither he nor I have that temperature measurement, we can't be too sure which way is worse. Approximately, in my case, the ambient temp was in the 70s F and the part of the hood I touched was about 105 F (by feel, I often test water for baking bread by feel and have a fair idea of how hot that is.) I also know from other sources that 125 F is too hot to touch for more than a few seconds, so that's my ballpark.

Also, there's confusion in the discussion between thermal distortion vs lens fogging.

It's really unfortunate that this effect isn't covered in detail in the manufacturer's docs nor in any magazine article I've ever seen. Certainly, the problem goes back nearly as far as I am old and should be in the arena of common knowledge.

I'm hoping that the short version of the lens hood will reduce the effect substantially while still protecting the front element and, if not, I'm contemplating drilling holes in it to vent the warm air quickly.

You probably want to make those holes as close as possible to the lens end of the hood, so that any light that leaks in will likely not strike the lens, plus, you need ventilation more at the closed end, anyway. I'm surprised that hoods aren't made with angled slots that don't allow light coming from in front of the lens to hit the front element; a hood could theoretically block all outside light while having lots of ventilation.

You can also paint the outside of the hood bright white, too, to cut down on heat, if it doesn't scare wary subjects.

Choderboy wrote in post #19434514
That article was just weird. Such extreme, sudden changes in environment are going to cause problems, hood or no hood..

True, but at least if the difference in temperature is only between air and glass, with no heterogeneous currents, then all small effects should be consistent, like focus, but focus is dynamic, anyway, and does not rely on exact lens positions for a given subject distance.

apersson850 wrote in post #19436861
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Simple solution: Move to Sweden.
Bring warm underwear and gloves.
.

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That won't help. . The worst heat distortion I have ever experienced was in Montana in 2014 when it was -4 degrees Fahrenheit, or -20 degrees Celsius. . In fact, in my experiences, heat distortion is normally more extreme in the cold winter months than it is in the hot summer months.


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Tom Reichner wrote in post #19437265
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That won't help. . The worst heat distortion I have ever experienced was in Montana in 2014 when it was -4 degrees Fahrenheit, or -20 degrees Celsius. . In fact, in my experiences, heat distortion is normally more extreme in the cold winter months than it is in the hot summer months.

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Exactly. I saw my worst thermal distortion that I ever noticed the first day I tried my RF800/11, on a very cold morning with bright sunshine. I thought that my lens was defective, it was so bad. I checked again a little later, and I could see the distortion changing through the viewfinder in real time, and then realized that it wasn't the lens.

apersson850 wrote in post #19436861
Simple solution: Move to Sweden.
Bring warm underwear and gloves.

LoL

Rod