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Oddly, when taking a photo of the Nikon D7500 which has an Eye-Start Sensor, my camera captures a red-purplish glow on the sensor while it is completely invisible to my eye. Take a look at the sensor right above the viewfinder:

enter image description here

No matter how closely I look with my naked eyes, even in darkness, I cannot see the dot in the Eye-Start Sensor yet my camera captures it every time, even under bright studio lighting.

  • Is my camera capturing infrared?
  • Can this be fixed internally?

I do not want to add an IR-cut filter to the lens because of impact to image quality and flare, put not all my lenses support filters and sometimes I use polarizers or ND filters which I would have to stack.

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    \$\begingroup\$ Do you get the same effect when the D7500 is turned off? With what camera are you using to take the photo? \$\endgroup\$
    – Michael C
    Commented Nov 30, 2017 at 18:39
  • \$\begingroup\$ No. There is no dot appearing when the D7500 is off. This photo was taken with a Pentax K-5 (original, non-II/IIs). \$\endgroup\$
    – Itai
    Commented Nov 30, 2017 at 19:17
  • \$\begingroup\$ Because there is a similar dot on the viewfinder, I suspect the auto focus assist light on the Pentax. \$\endgroup\$
    – user50888
    Commented Nov 30, 2017 at 19:27
  • \$\begingroup\$ Assist light is disabled and the viewfinder dot is barely noticeable while the one in the sensor is much brighter. \$\endgroup\$
    – Itai
    Commented Nov 30, 2017 at 19:40
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    \$\begingroup\$ Are you concerned about this as a "defect" because you often shoot images containing infrared light sources, or are you concerned about a possible impact on image quality in normal scenes? \$\endgroup\$
    – mattdm
    Commented Dec 1, 2017 at 14:40

4 Answers 4

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If you only see the effect when the D7500 is turned on but not when the camera is turned off you are almost certainly seeing near-infrared light recorded by the camera taking the photo.

It's fairly common for most digital cameras to record such light. The easiest example I can think of are the near countless photos people have posted in various forums of an infrared remote control for their television pointed at the camera with one of the buttons pushed when the photo was taken.

(If you also saw it when the D7500 were turned off it is possible it could have been a specular highlight from your lighting reflecting off the exterior coatings on the Eye-Start sensor - but that does not seem to be the case since you don't see it if the D7500 is turned off.)

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  • \$\begingroup\$ ...And infrared LEDs are very commonly used as emitters in proximity sensors. Lots of mobile phones have them, too. \$\endgroup\$
    – Blrfl
    Commented Nov 30, 2017 at 19:25
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    \$\begingroup\$ @MarkRansom - See sample image It does not produce what the eye can see. I'm doing product photography, not shots for the X-files ;) \$\endgroup\$
    – Itai
    Commented Nov 30, 2017 at 21:21
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    \$\begingroup\$ @Itai no camera captures colors identically to the eye. What I'm saying is that seeing extra is better than seeing less, and doesn't rise to the level of calling a "defect". Your expectations are simply too great. \$\endgroup\$
    – Mark Ransom
    Commented Nov 30, 2017 at 21:26
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    \$\begingroup\$ @Itai, your camera already has an IR-cut filter. If you're not seeing issues when taking pictures illuminated by incandescent lights, it's working as designed. If you want to eliminate concentrated IR sources like the camera's Eye-Start sensor, you'll need to add a second, stronger filter. \$\endgroup\$
    – Mark
    Commented Dec 1, 2017 at 0:07
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    \$\begingroup\$ See the answer below from Agent_L, this is NOT a defect. all digital camera's will detect and show infrared sources. There are even people who photograph using only the infrared light spectrum. \$\endgroup\$
    – HTDutchy
    Commented Dec 1, 2017 at 14:39
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Is my camera capturing infrared?

Yes. All cameras are capturing some infrared. Digital cameras are particularly good at capturing IR, that's why most of them have internal filter that dims out the IR.

Can this be fixed internally?

No. It cannot be "fixed" at all, because it's not considered a defect. The camera likely already has internal IR filter, but it's not ideal (nothing is). You can try external filter, but it either won't help (same as the internal one) or degrade lower portion of visible spectrum (filter out visible red light).

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Run this test: Image your IR TV remote while pressing the volume up button. Can you image the IR LED outputting IR?

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    \$\begingroup\$ Instructions unclear, neighbors complaining about noisy TV :) \$\endgroup\$
    – rackandboneman
    Commented Dec 1, 2017 at 1:07
  • \$\begingroup\$ @ rackanboneman - The only solution is -- sprinkle pixel dust. \$\endgroup\$
    – Alan Marcus
    Commented Dec 1, 2017 at 1:45
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    \$\begingroup\$ An alternative would be the holding down the "Channel +" button. But I'd only recommend this before 9PM, unless you have a very open mind :) \$\endgroup\$
    – Wossname
    Commented Dec 1, 2017 at 10:45
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    \$\begingroup\$ Or just any button and not pointing it at the TV (or doing it in another room)... \$\endgroup\$
    – RobIII
    Commented Dec 1, 2017 at 20:03
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I believe this is the IR sensor that detects your eye (or most other things) near the viewfinder so it can switch off the display screen for easier viewing. Without this, your eye when it is on the viewfinder, would get the glare from the screen below. I am a Canon guy, but I think this is the same function on mine as well.

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    \$\begingroup\$ I'm pretty sure Itai wasn't asking about what the red-purplish dot is or its function (after all, he identified it as the Eye-Start Sensor); rather, Itai was asking if the camera that took the picture of the D7500 is seeing in the IR spectrum (because the Eye-Start Sensor light is infrared). \$\endgroup\$
    – scottbb ♦
    Commented Dec 1, 2017 at 20:52

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