Here's the results of a test done this evening with the K3 + 16-85mm (a very good lens) to show signal to noise ratio in practice. Taken outside, bright but overcast, uniform light. Subject was a neutral (very dark grey) board. All at ISO 200 and f8, defocussed to minimise the effect of imperfections of the matt painted surface. All images are 800x800 pixel crops so the forum images should show exact pixels. RAW (DNG) files, no noise reduction in camera or in post processing (with Affinity Photo), converted to highest quality jpegs for the forum.

Here's the base image. Camera chose 1/25sec to give a mid-grey (as it should). Some noise apparent but not much and easy to remove in post processing (the default noise reduction in Affinity Photo does a good job).




Now an image underexposed by 4 stops (at 1/400sec) with + 4 stops added in post processing to bring the average brightness up to base level. Although the overall brightness is the same as the base image, there's a lot more noise. That's because the noise from the sensor has been increased by 4 stops in post processing. More difficult to remove in a 'real' picture because there's more of it competing with the detail that you'd want to retain (the software wouldn't know what is noise and what is 'real' detail).



Finally, an image overexposed by 4 stops (0.6 sec) with -4 stops added in post processing to bring the average brightness up to base level. Although the overall brightness is the same as the base image, there's less noise. That's because the noise from the sensor has been decreased by 4 stops in post processing. You've got to look very hard to see any noise, and that's without any noise reduction at all.



In a real picture, the same level of noise will be present everywhere. However, it will be more intrusive in darker areas because there is less light to mask it. It's up to you how much noise is acceptable and to ensure that it is below that level in the final image. Noise reduction in camera or post processing software is good, but it can never know whether the random specks in a shadow or dark area are sensor noise or vital detail that you need to see.

I hope that makes sense!

Steve

A different lens isn't likely to make a difference to noise, noise comes from the sensor and electronics. It's always present in the electronic output from the sensor (thermal noise etc.) and the amount of noise is pretty well independent of the light level. If the signal to noise ratio (i.e. light level to noise level) is big enough, the noise is not noticeable. If the signal level (i.e. light level) is low, then the noise is proportionally bigger relative to the light level so is more noticeable. Low light level might be because of overall low exposure or because of a darker part of the image (e.g. dark colour or shadow).

Noise can be reduced or even eliminated in processing the output from the sensor - either in the camera or by the user - but something else will be lost (e.g. resolution). It's a balancing act. If you're post-processing RAW, you do noise reduction with your post-processing software (although I may have read somewhere that the camera may apply some noise reduction to RAW). Try different options and see what works best for you. If you're concerned with jpegs from the camera, adjust the camera noise reduction settings to what works best for you. And 'what works best' may depend on the type of subject (e.g. dark overall or bright + shadows).

Noise is an issue for all signal processing, the same sort of thing applies to audio, radar, radio telescopes, particle physics experiments etc. etc. etc. It's always there, the balancing act is to get rid of as much as you need without affecting the useful stuff in the process.

Not sure if that helps!

Steve

Thanks. Neither wheat or barley, just random grass in the verge at the edge of a field. Now you mention it, I think you're right about a hint of a starburst in No. 1.

Steve

Well spotted. Good colours, good clouds and a nice feeling of gathering the crop in, which isn't that common since a combine can do it in a few hours.

Your fields are looking more interesting than mine at the moment, which is why I'm looking in the verges at the edges.

Steve

It was going to be a bog-standard ladybird shot. But then it headed off and the only way to get a shot was from the other side, into the light. It only travelled a few inches before the dog made it clear it was time to move on. Enough to get a few shots, though. And here they are. The starburst in the second is entirely accidental, but I've kept it there because I like it. And as coker says in another thread "Any insect will reflect. Somewhere."

K3 + Sigma 105mm macro.

Comments, thoughts etc. welcome as usual.

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Steve

+1. Consistent with my experience with a K3. And every digital camera I've owned has produced noise in some circumstances and to some degree. Always possible to get rid of it in post-processing, but at the expense of something else.

Doesn't worry me, though. I've got pictures on the wall that don't look good from very close up but are excellent from normal viewing distance. OK, they're paintings but the point is the same: the artist produced a picture that is good for the way in which it would be normally seen. They simply weren't interested in what it looked like at the level of each mark produced by each hair of the brush. I commend that approach for photography, too.

Sounds an interesting approach to processing - must try it!

Steve

But the drawer doesn't contain the one you need now that has the latest connection so you've got to buy one, along with adapters to connect to all the older sockets.

Steve

Find the local one and use often.

Or do what my son-in-law's father did - build lots of sheds. You've got to admire a man with 3 sheds (or was it 4?)...

Steve

I can remember picking up a DSLR for the first time and thinking 'Who'd want to carry that weight around?'. It's still a factor, that's why I've got a Q as well as DSLR. But look at what TV reporters are doing with smart phones. When something so capable can be carried in a modest-sized pocket, and as Jetsam1 says, it's also internet, basic computer, gps, and so on (and even occasionally a phone), there's got to be a good reason to spend £££ on a separate camera. I've got my reasons, you've got yours, but most people don't and never will have. So the camera manufacturers have got to concentrate on people who are prepared to spend £££ on a 'real' camera will actually buy and shape their business to the reduced market.

Will Olympus camera division survive under a private equity company? Well, the assets are mainly the camera-related IP, and it's a Japanese buyer, so asset stripping and shutting down is unlikely IMHO. The big questions are whether the buyer can make Olympus cameras profitable and, if so, who will buy a small but profitable specialist camera company in a few year's time? Well, Ricoh did it with an unprofitable one a few years ago and it's still here... Anyone fancy speculating on whether they might add a specialist in small MILCs after a few more years??

Steve

Very nice splashes of colour to add interest and depth to what would have been a very green scene. Well spotted, well taken. And it shows how useful a Q-in-the-pocket can be.

Steve
PS: I thought that I was dealing well with the sad demise of my 06, but now you've shown (again) what it can do I'm getting all emotional... You're a bad man, Mr Womble!