Why are my blacks coming out so noisy on a Pentax K-30 DSLR when using RAW format

Question

I'm a new DSLR user with an older model Pentax K-30, using a 18-55@43mm lens (The lens that it shipped with).

I don't yet understand what all the settings mean, or how they are used, or the impact of choosing a specific setting, as I previously just used a mobile phone set to Automatic.

I'm using RAW format to photograph small scale miniatures in a light box against a matt black background.

The objects that I am photographing a non-reflective and are lit by two double LED battens with a diffuser mounted in the top of the lightbox, and a independent LED light bank placed on top of the camera in place of a flash.

The camera is set to macro mode. The camera is set to automatic, but there are numerous other settings that I believe are set independently, and which remain as they were when I received the camera.

The backgrounds are coming out a mottled blue\gray with a lot of noise on it, rather than black. The objects that I'm photographing look washed out. Vibrant colors are dull, and the blacks are gray.

I don't have this problem other colored backgrounds. I'm guessing that this has something to do with them being much lighter.

For example.

Taken using the Macro preset, and other setting on automatic. According the meta data this is equal to

f/7.1
1/25s
ISO 12800

I'm using a tripod and these are the settings that the camera\preset chose.

_{Click for full size}

The gradient is because this background is curved, not flat, and this not lit from the same angle along it's length. I'm not worried about that, it's . Only why it's so noisy.

I can correct some of this in photoshop, but it impacts on the rest of the image too.

It has been suggested several times that the high ISO indicates that there is insufficient light. This is a definite possibility which I am not discounting as being the correct answer. The camera itself has a low light indicator and a long expose warning indicates. Neither of which are being displayed. Hence me looking for other - less obvious - answers.

The object appear well lit to the naked eye. I have turned the LEDs up to a high setting, but not all the way up. If I turn them up any more the gray areas of the objects that I am photographing turn white, and the white areas become over exposed and all details are lost. Leading me to question whether there is another setting that I am not aware of which is causing my problems (For example, some form of manual override to the automatic settings).

Answer 1

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.

Answer 2

The backgrounds are coming out a mottled blue\gray with a lot of noise on it, rather than black. The objects that I'm photographing look washed out.

I don't have this problem other colored backgrounds. I'm guessing that this has something to do with them being much lighter.

The main thing I am seeing is that the metering mode is being fooled by the black background and you are not compensating for that. The meter expects to see an average scene brightness, so it thinks black is average (grey) and overexposes it. This is causing the black background to record as grey and your subjects to be washed out.

You need to use exposure compensation (p20 of the manual), or manual settings, to prevent the overexposure. And then the results should be more comparable to what you are getting with the other background colors.

Dark parts of a scene are always noisy; because they contain very little light. Your problem is that they are being made bright enough to make the noise visible/more visible.

Answer 3

I don't yet understand what all the settings mean, or how they are used, as I previously just used a mobile phone set to Automatic.

Mobile phones usually use aggressive noise reduction and increased contrast (reduced details in dark parts of image) so you won't see a lot of noise generally. This also turns all details cartoonish when the light is lacking.

Dedicated cameras usually do not have aggressive noise reduction enabled by default specifically because it destroys fine details.

Answer 4

How does the exposure automatic work?

As already pointed out, the exposure automatic works best if there is a motive with a usual distribution of light levels. It will fail in edge cases like an image of a snowy landscape as well as a black cat in a coal mine.

As soon as you enter a situation where you can see (at least after taking the first image and seeing it on the lcd screen) that the automatic fails, you can either use exposure compensation or switch to full manual settings.

In a studio setting as described above, I would recommend using fully manual mode.

If you are going to use exposure compensation instead, see if you camera supports center metering. If will then try to use the light situation in the center more than the surrounding background for establishing exposure. This will offer a better starting point.

Photography is about light

And you are lacking light.

You are on 1/25 (indicates not much light), aperture 7.1 (saying do not allow much light in, in exchange for more depth of field) and ISO 12800 (which is the max your camera can go on auto - which also states you are low on light.

Cameras usually capture very grainy images when pushed to their ISO limits. And this is why your image is so grainy.

But I have LED lights...

Yes, but their intensity is pretty low. There is a reason why in the past, Photographers used powerful studio strobes - or nowadays more and more powerful LED spot lights to light their images - especially when in a studio setting. Note that sunlight is much much more intense than we usually notice. At least when comparing to some inexpensive LED light.

You can indeed work with moderate lighting and a tripod, however, as you can increase exposure length into the area which cannot be hand held. At least as long as your subject is not moving.

What can I do to get good color contrast?

You can expose the image correctly. Switch all settings to manual. Then start to reduce ISO until your main motive looks exposed correctly.

This should set a good starting point.

Now my light areas are blown out and my mid tones are ok

Two things might get in the way:

• You may need a more diffused light to dampen specular highlights
• If lateral contrast is too big, your light might simply be too close to the subject. Due to the inverse square law, light diminishes not linear with distance. You lose much more light in the first 3 feet than in the next 3 feet. This can be exploited to either create more contrast by placing the light nearer to the subject. Or farther away to create less contrast.

There is a website explaining this concept: https://fstoppers.com/education/peter-hurley-explains-how-inverse-square-law-applies-photography-167674

You can test this by tuning down the light and placing it closer to the subject and take a picture and then turning up the light to max and increase distance until you reach a good exposure again. If you compare both images, you will notice they look differently although both are correctly exposed.

But my black look still grainy, and not all black

These are two separate problems. Let's sort out the grain first.

There is a rule about the exposure triangle (Exposure, Iso, Aperture) that any change in one values can be balanced by a step in the opposite direction on one of the remaining settings.

So if I want to go one step down in ISO (12800 -> 6400) I need to counter this by either doubling the exposure time 1/25 -> 1/12 or change the aperture one step more open.

This means you can go from 12800 -> 6400 -> 3200 -> 1600 -> 800 -> 400 -> 200 -> 100 in 7 steps. This would mean that 1/25 would become 5 seconds.

A tip: there are exposure calculators like the Photo Pills App (or many free websites) that help you calculate these things, if you have to. You can also just try out and make the exposure longer and longer until you get a decent exposure. You are probably getting a not too grainy picture starting at around ISO 400 or less.

More on the exposure triangle here: What is the "exposure triangle"?

How to get real black background?

You need to make sure that not that much light hits your background - or is reflected from it.

For lights, photographers usually use something like a grid mask in front of the light to prevent stray light.

Or you can use less reflective background material. Like black velvet, black molton fabric or similar.

Setting up lighting should be done with clear intent. You need to understand, what ambient light you might be getting into your exposure and what each light provides for your shot. If you just place some lights here and there, your shot will look like that.

If the problems with grain and correct exposure has been sorted out, you can start playing with the light placement and see what each one does. You will need to compensate in your exposure a bit, but you should have a good starting point for doing so.

It also helps to understand some of the fundamental rules with light like what is hard/soft light and how to get it, what does diffused light do, what if light falloff and the inverse square law.

See here for more inspiration What do I need to get photos with a unifom black background (not with post)?

But why did the camera not indicate exposure warnings?

Because it still could fit in the scene into a practicable exposure triangle setting. The ISO limit was not broken and the exposure was barely ok to be handheld.

But as you saw for yourself, the image was no longer usable.

My Mobile Phone captures better images

Yes. For one, the mobile phone in question is probably not having a 10+ years old sensor. There has been a lot of progress in the last years.

Another point is, that a raw image is mostly unprocessed. It is expected that you give it a pass in a development program like Lightroom to refine contrast, colors, sharpness and possibly reduce noise. Your mobile phone is doing that for you and is quite good a t it. However, you will see a hige difference if you really zoom into a DSLR image with good exposure and a mobile picture.

Please not that this margin of quality might diminish more and more as AI features enter the mobile camera world, as AI can insert details into an image that were simply not captured. A good example is recent Samsung phones which replace the moon in a picture with a rendered fake moon with more details.

Answer 5

You've received solid advice across the board but I get the impression you're not understanding it. In particular where you said, "I've boosted the light to the extent that the lighter areas are totally blown out. I think that something is incorrectly set on the camera."

You are correct, there is something incorrectly set on the camera and that something is the "Automatic".

The camera automatics are using reflective metering, which implicitly assumes reflectivity from an aggregate gray level. In the circumstances you describe, this will not work!

Turn off automatic exposure!

Ideally you would use an incident light meter to determine the manual exposure settings to use. If you don't have one, trial and error will work.

Set your F-stop to a reasonable value for what you're shooting, use F-8 if you have no idea where to start.

Set you ISO to an acceptably low noise value, use 400 if you have no idea where to start.

Now vary only your shutter speed until you get a decent exposure.

Once you have a decent picture you can alter the other parameters proportionately to maintain a proper exposure.

EDIT

It occurred to me that since you are using a variable intensity LED light source you may want to go with a fixed shutter speed, start with 1/60, and vary your F-stop instead.

The reason for this is that the LED light is actually flickering at a high rate duty cycle that will average out to your eye and to a slow shutter speed. A very high shutter speed may actually capture partial images if it's fast enough to be in the range of LED flicker speed. Just avoid that issue with a slower shutter speed. Plus it's easier to vary the F-stop.