Why does a black background look noisy and gray in RAW on my Pentax K-30?
Asked 11/26/2023
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2 answers
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I’m photographing small miniatures in a light box with a Pentax K-30 and the 18–55mm kit lens at about 43mm. I’m shooting RAW on a tripod, using the camera’s macro/auto settings. The scene is lit with LED lights and a diffuser, with a matte black background.
A typical exposure chosen by the camera is f/7.1, 1/25s, ISO 12800. The black background comes out mottled gray/blue and very noisy, while the subject looks washed out and less vibrant. Lighter-colored backgrounds don’t show the same problem.
Why is this happening, and what settings should I change to get a cleaner black background and better color?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
2y ago
2 Answers
5
I can't answer in regards to the camera itself, as I don't know Pentax at all, but…
You're very short on light.
f/7.1 1/25s ISO 12800
You can get away with 1/25s exposure time if you're on a tripod. Hand-held is expecting too much.
Your ISO has ramped up probably as far as it can go, to compensate for the lack of light. This means you have a lot of 'artificial' amplification going on in your shot. Your noise floor - random background & any inherent noise in the sensor - is being amplified as much as the rest of the shot.
For macro, as your depth of field is always going to be short anyway, you could open up your aperture as wide as it will go & not see any noticeable difference in DoF.
If you're used to a modern smartphone, what you're missing is the clever image manipulation they all do by default these days. Multiple exposures to extract maximum detail from different lighting levels in your scene, noise reduction & sharpening. These are invisible to the end user, it's all just done for you.
With a DSLR, basically you have none of that. You need to compensate for these things all by yourself.
Originally by user57929. Source · Licensed CC BY-SA 4.0
user57929
2y ago
0
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Two things are happening:
-
The camera is overexposing the black background. Auto metering tries to make the scene average to mid-gray, so a black backdrop gets lifted toward gray. That also makes the subject look washed out. Use negative exposure compensation or switch to manual exposure so the background stays dark.
-
ISO 12800 is causing heavy noise. That ISO means the camera is strongly amplifying the sensor signal, including shadow noise. RAW also won’t apply the strong noise reduction and contrast boost that a phone typically does.
What to do:
- Put the camera on the tripod and use a much lower ISO.
- Since the camera is steady, use a longer shutter speed instead of high ISO.
- If depth of field allows, open the aperture wider than f/7.1.
- Use exposure compensation or manual settings to keep the black background black.
In short: lower ISO, let the exposure run longer, and don’t let auto metering brighten the black backdrop.
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