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How can I reduce blurriness when taking a photo in the dark, using only UV light?

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I'm trying to take a photo of a white paper heart in UV light, to make the heart look like it's glowing. I expect that the heart is going to look, well, purple, rather than white.

I'm taking this picture against a white wall with the regular lights off, at night, so pretty much the only source of light is the UV light.

blurry photo of purplish heart

Unfortunately, it came out... rather blurry around the edges. The color is fine, the background (which is a white wall) is fine... but the edges of the heart itself are just not coming through clearly.

What can I do to have the edges of the heart show up more clearly when photographing in the dark, using only UV light?

I'm using a GoPro Hero 7 Black, set to automatic Superphoto (but I can adjust the settings).

Why should this post be closed?

2 comments

is this image cropped? scottbb about 1 month ago

@scottbb - yes, rather heavily (the original image was too large to upload and cropping was the easiest way to shrink it) Mithical about 1 month ago

1 answer

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Possible problems, with their solutions, are:

  1. Inability to focus properly in the dark.

    Put the camera on a tripod. Focus and compose with the lights on. Depending on the camera, you may have to switch it to manual focus mode. If your camera is too dumbed down to allow that, then it is inappropriate for this situation. Use a camera that can be manually focused, and then retain the focus setting.

  2. UV light may not focus the same as visible light.

    This applies to glass lenses, not mirrors. However, it would be very unlikely to use a mirror lens in a room in a house like this. Most mirror lenses are long focal length.

    The index of refraction of glass varies with wavelength (color). Your camera lens was designed to deal with this by careful formulation of the glass, and use of multiple elements to keep the overall focal length reasonably constant over the visible spectrum. However, focusing UV light the same as visible light was not likely a consideration. In fact, UV focal length may have been sacrificed to get better consistent visible focal length.

    The solution is to block UV. Perhaps your camera already does this, in which case it is not necessary. I would certainly start with a UV filter over the lens. You can then experiment and see if it actually matters.

so pretty much the only source of light is the UV light.

Keep in mind that you're not actually photographing in UV. You are photographing the visible light emitted by the paper due to phosphorescence.

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