Is it ok to use IR filter for photographing sun?

Question

I recently purchased cheap IR filter 720nm from Amazon to see whether I will be able to replicate effect with which your camera can see through thin plastic. I was wondering whether it could be also used for taking pictures of sun since I believe it should be blocking enough of the sunlight. I think sun would be just black and white but I am ok with that. Or maybe not, Sun is pretty strong and it is a cheap filter after all. So, some colours could potentially appear.

The camera I am planning to use is iPhone 14 Pro.

iPhone can supposedly take pictures of the Sun by default without taking too much risk. Does using IR filter makes things safer? I am not asking what is the proper filter, I am asking whether the IR filter is sufficient enough for iPhone.

Answer 1

There is already an IR blocking filter in all consumer cameras and if you are blocking almost all visible light you are eliminating almost all risk of damaging the camera. That's also the reason why your idea of seeing through thin plastic with camera might work worse than you'd expect. The strength of IR blocking varies.

That said, leaving the camera stationary pointing at the sun for prolonged period is not safe in any case because there are a lot of sources of heat inside camera and rarely there is any active cooling. The sensor would at the very least get heated by the adjacent IR blocking filter. Yes, I am sure you can take a lot of photos of the sun with short exposures. No, I am not at all recommending keeping the camera pointing at the sun in fixed position.

I also highly doubt the iPhone is somehow safe from damage without any filters attached. It might detect sunlight and close the aperture and maybe even use ND filter internally (I did not hear of it) for live view but it won't prevent damage if you somehow set up long enough exposure, opened aperture and fix the iPhone pointing at the sun. In that sense it's not safer than any other camera equipped with same speed lens.

Answer 2

Though given one material (glass lenses on DLSR, injection molded plastic for more affordable camera lenses) the diffraction depends on the wavelength of radiation, to obtain a sharp image, the camera concentrates radiation on a small area. In the case of directly exposing a lens to the sun (i.e. alignment of the sun along the optical axis of the camera), this carries the risk that film (analogue technique), or sensor (digital technique) are irreversibly damaged.

Likely, the magnification of the camera lens alone will not suffice to observe sun spots. But if you find one aluminized mylar filters from the safety glasses sold around solar eclipses mount top of the lens, your device should be much safer. There is a standard for them (ISO 12312-2). Without endorsement for a particular source, regarding the upcoming solar eclipse in the Americas (Saturday, October 14th, 2023), the American Astronomical Society compiled a large list of suppliers. Some of them for about $1 a pair.

Answer 3

I would purchase a solar filter if I were you. If the cost is too much for your budget, you can add a cheap solar glasses film to a UV filter. Make it secure. I have an IR filter, but it allows infrared light to pass through. I am not certain it will prevent eye damage. If you limit the time of exposing the censor to the sunlight through the IR filter, it probably will work. I would use your camera's live view so you don't worry about eye damage.