Can high-tension lines degrade image quality?

I've been trying to photograph foxes, there den is under many high-tension lines (about 2/3 mile upstream from a 35,600 kW power generating dam). I'm using a Canon 400mm F2.8 L USM lens on Canon EOS 5D III and 7D II bodies. I'm sitting for five or six hours each session, directly under the wires.

The images are soft - it looks like I'm shooting through heat shimmer. It isn't that I'm missing the focus - there are no sharp points anywhere in the image. I've shot a few hundred thousand shots with this gear on this tripod. I miss the focus now and then, but the set up has been proven repeatedly, so we're not dealing with motion blur. I'm in a blind only ~35 feet from the den, hard to believe there's enough heat shimmer to distort an image. The same gear works well once I'm away from the high-tension lines.

Is there something that could be interfering? I wondered if the magnetic field from the lines might be strong enough to be corrupting the card. But, I'd expect that to give file read/write errors rather than affect the image. (The affect is the same writing to both SD and CF cards).

Anyone have any thoughts?

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    \$\begingroup\$ I doubt the field is having an effect on the cards. The only thing I can suggest as an experiment is to to try manual focus and no image stabilization of any kind. Complete shot in the dark! This sounds like an interesting issue. \$\endgroup\$ Apr 30, 2020 at 0:28
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    \$\begingroup\$ What exposure values are you using ? First eliminate the standard issues. Also note that "a few hundred thousand shots" could mean some fault has developed with camera body or lens or both that only affects particular shooting conditions. \$\endgroup\$ Apr 30, 2020 at 0:51
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    \$\begingroup\$ As to the card: A strong magnetic field might affect the card. We then expect random bit flips at first. This would invariably lead to corrupt images, not an evenly distributed soft effect. \$\endgroup\$ Apr 30, 2020 at 5:49
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    \$\begingroup\$ Could you post an example photo? Or at least a link to one? \$\endgroup\$
    – Michael C
    Apr 30, 2020 at 9:32
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    \$\begingroup\$ @Kai Mattern - Moisture in the lens was one of my early thoughts. There's none visible when looking through the lens - probably not a definitive test. The issue has occurred on several different days, and not occurred on several days elsewhere. \$\endgroup\$
    – NYSW3636
    Apr 30, 2020 at 11:51

3 Answers 3


As you said, one would expect file errors if it was affecting the cards. And I think it would take extremely strong interference to cause an issue with the ultrasonic focus motor or electronic aperture.

I sometimes take pictures under high tension wires with no apparent effects... the wires are close enough, and carrying enough power, that I can hear them buzz and pop.

Are you shooting through anything? I once had a spider build a web inside a lens hood... And shooting through foreground obstructions like blades of grass will cause that effect.


Magnetic fields have no impact on cards. These are unlike previous storage devices that did rely on magnetic fields aligning iron particles on plastic media.

For more: https://electronics.stackexchange.com/questions/36921/does-magnetism-affect-sd-cards

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    \$\begingroup\$ Magnetic fields do affect SD cards. SD cards are based on NAND flash technology that have a floating gate transistor. The floating gate has trapped electrical charge. As we know, a very strong and rapidly changing magnetic field can induce an electric field, destroying the stored charge. The static magnet test does not prove anything other than that a strong non-changing or slowly changing magnetic field does no harm. This says nothing about a very quickly changing magnetic field. \$\endgroup\$
    – juhist
    Apr 30, 2020 at 15:14
  • \$\begingroup\$ sure, question linked above suggests that indeed a very strong magnet can have an impact, but that same magnet would have negative impacts on other items, including credit cards, etc and in significant cases, your blood. If you feel this answer is incorrect, pls downvote and i will remove \$\endgroup\$
    – cmason
    Apr 30, 2020 at 15:21
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    \$\begingroup\$ No, not so incorrect that I would downvote it; just wanted to say that there are cases a magnetic field can affect SD cards. For example, ionizing high-energy electromagnetic radiation is essentially a changing magnetic field (and along with it, a changing electric field), and can cause lots of damage to not only living organisms but also flash memory. \$\endgroup\$
    – juhist
    Apr 30, 2020 at 15:23
  • \$\begingroup\$ @cmason - thanks. That's good info. I suspect I'm reaching here, but haven't found anything else to check. \$\endgroup\$
    – NYSW3636
    Apr 30, 2020 at 15:53

I have a WAG!

Your cropped image fox crop has a bunch of fine wavy lines that remind me a little bit of the effect of high speed motion captured with an electronic rolling shutter.

Yes I know, you don't have an electronic shutter, bare with me.

The rolling electronic shutter effect results from reading the sensor line by line on a live image that's changing as the readout rolls through the sensor array.

Suppose (my WAG) that the sensor readout row by row of the static image, i.e. not an electronic shutter, is having small varying signals induced into it by the high electromagnetic field oscillation. This would be prior to digitization check-sums so no detectable image error would occur. This would be not only before the jpeg creation, it would be before the raw file creation.

If you happen to have access to a small Physics lab with a Helmholtz coil, you could test it.

  • \$\begingroup\$ Thanks, that's an interesting idea. Now to figure out where I put my Helmholtz coil.... I'm not far from Dartmouth College, they must have one. \$\endgroup\$
    – NYSW3636
    May 2, 2020 at 18:25
  • \$\begingroup\$ @NYSW3636 - Dartmouth would almost certainly have one and I bet you could convince a physics prof that it would make a great undergraduate experiment. Dependencies would include: Camera Model, field strength, relative directionality between field and camera in 3-axis. Possibly ISO settings as well. \$\endgroup\$ May 2, 2020 at 20:08
  • \$\begingroup\$ Similar thoughts: reading the sensor (into processor then to card memory) involves electrical events, which might be effected by strong local voltage variations (AC current). Steven Kersting's report of shooting near high voltage lines without issue runs against this hypothesis, but perhaps it's just idiosyncrasies (differing distance to voltage source, perceptual differences of varying individuals, etc.). You could buy a cheap Gauss meter. If the field in your blind is off scale, 'nuf said. And if not (if lower), maybe you could find an in-home source (say, near a clothing iron) to test. \$\endgroup\$
    – ZenGeekDad
    May 3, 2020 at 17:51
  • \$\begingroup\$ @user10216038 Undergrad? Heck, I was going to suggest putting a grad student to work. Dartmouth supposedly has a supply of students who couldn't leave campus. They're not in class, I may get lucky and find someone to put to work. And, I've been in touch with Canon. Tech support has kicked me up to an engineering group. That makes me guess I'm not the first one with a problem, but also that the problem is rare enough that the first line techs don't have an answer. Will post what I find out. \$\endgroup\$
    – NYSW3636
    May 3, 2020 at 22:55
  • \$\begingroup\$ @ZenGeekDad - My first thought was to call the power company. They probably have a good idea of the field strength already. And location I'm having the problem is an easy ten-minute walk from the dam. Probably close enough to get someone curious enough to measure it if it comes to it. Also have found a phone app. Downloaded it, but suspicious of it's accuracy. \$\endgroup\$
    – NYSW3636
    May 3, 2020 at 22:59

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