Pure Black Background Problem!

[radicalgel]

<p>Hey,</p>

<p>I shoot with a Nikon D300s and use lightroom to process my images. I was recently trying some grided portraits where I was exposing the model's face and letting everything in the background go pure black. I chimped a lot and also confirmed that the background was truly black, by zooming in so I can see just the background, then using the RGBL histograms to make sure they all read 0. However, when I opened the RAW images in Lightroom and pulled the blacks slider that defaults to 5, back to 0, the histogram miraculously showed no clipping in the shadows and my background was now a murky gray. Does this mean that lightroom is actually pulling detail out of the RAW, or is it just shifting the blacks to ~90% gray.<br>

My light meter told me, that in several of my shots, the background was almost 5 stops or more underexposed, which to my knowledge translates to pure black, where the sensor is picking up no light and hence no detail. I hope someone here can clarify my doubt and tell me if I am missing something or doing something.</p>

[francisco_disilvestro]

<p>That detail is in your RAW file. Assuming you were working at the base ISO of 200, the D300s is capable of recording plenty of detail at 5 stops of underexposure. It is actually the same as setting the ISO to 6400.</p>

<p>When you check the image and histogram in the camera LCD, you are not viewing the RAW file but at a jpg rendering based on your parameters (color space, profile, etc) and you will not see those details below 5 stops of underexposure.</p>

<p>Back in lightroom, when you pull the black slider to zero, those details appear. What you actually should do is to use the black slider up to the value where all your unwanted detail disappears</p>

[george_ghio]

<p>Two words of advice:<br>

"Black Velvet"<br>

Wonderful stuff if you want a black background.</p><div></div>

[Charles_Webster]

<p>Black velvet or black paper, the secret to getting a truly black background it to keep the light off it.</p>

<p>Flagging your lights so they fall only on the subject, not the background will relieve you of all the post-processing trouble later.</p>

<p><Chas></p>

[Mattman944]

Pure gray or noisy gray? If noisy gray, then are pulling detail out from the depths.

 

If the black is really black when your sliders are set for good results, don't worry about it. If not, get a blacker

background or keep the light off it as others have suggested.

[radicalgel]

<p>Thanks so much for the replies!<br>

@<a href="../photodb/user?user_id=6211748">George</a>: Black velvet is awesome and that's exactly what I used! :)<br>

@<a href="../photodb/user?user_id=3861002">Francisco</a>: Thank you for the detailed reply. Very informative.<br>

about this "What you actually should do is to use the black slider up to the value where all your unwanted detail disappears"<br>

I realized that when I do this I also start to clip details on my subject in the deep shadows or black hair. I guess it's my fault that I only checked if the background was black but didn't bother to check if any part of my subject was clipping. It amazes me how this camera picks up detail in near darkness.<br>

So I would like to know what your advice would be to achieve pure black in camera? and is it possible to tweak my picture control settings so that the histogram in camera doesn't mislead. I current have it on 'Neutral' modified as follows:<br>

Sharpness: 6 (to check focus)<br>

Contrast: -1<br>

Brightness: -1<br>

Everything else to default.</p>

 

[radicalgel]

<p>UPDATE:<br>

In the mean time I tried a test suggested at another forum. I took and image at f8.0 1/250th with the lens cap on and Lightroom still pulled back "something from nothing". 'Black' @ 5 gave me R:0 G:0 B:0, where as, 'Blacks' @ 0 gave me R:5 G:2 B:3. Could someone please explain what the issue is here?</p>

[francisco_disilvestro]

<p>The issue here is "noise". It is a fact of real life, present in every digital sensor in a higher or lower level. It actually get worse for long exposures and that´s why "Long Exposure Noise Reduction" is for. This method of noise reduction will take a second shot without opening the shutter just after you take your picture and substract pixel by pixel. This, only for long exposure times.</p>

<p>In most cases, you don´t need to pull the Black slider at 0 in Lightroom. You can also play with the tone curve for better control of your shadows</p>

<p>Regarding the in camera histogram and preview, I´m not sure you could achieve a high level of precision, your settings seems fine. Besides to achieve pure black you might always need to do some post processing.</p>