Ok. Now what Jim said about evaluative/matrix metering makes sense to me now.
So, I'll simplify my proposed comment even more by going with something like:
"....contemporary camera meters are calibrated to output their manufacturers' set image lightness...."
which should cover all bases, hopefully 🙂
Would you and Jim be comfortable with that if you saw it in my posts?
Another set
had to klean up my desktop theres that many images .
preview histogram
Live histogram
this is showing clipping
On a side note:
BBcode, like HTML tags, have no forward slash "/" in the opening tags. The closing tags have a forward slash.
Also, opening/closing tag pairs need to match otherwise you end up with "ugly" looking posts with messed up code being displayed.
In your above post, all you need to do is delete the forward slash in the opening quote tag.
awesome thanks for that, i hope i can remember for the next time.
No problem.
Why? "What are you on now?", please?
Jim is shooting MF Hasselblad.
0.1 EV - not a huge tolerance.
I'm not sure which tolerance you are referring to.
I was referring to the 18% grey I originally mentioned and Jim's ~12.5% and Iliah's 7%.
some go to 22%
Also Nikon Z 9 and Leica Q2M.
Hey Ted, having you and Jim in the same forum is neat!
What happens with those histograms when you start gradually lowering the exposure?
The raw histogram tells you how far your channels are from clipping in the raw data. If there is at least 1.33 stops of unused headroom, then you know that you could have exposed 1.33 stops more, and pulled the conversion down 1.33 stops.
There are more or less 3 points at which clipping can occur. The first is when the photosites are being read out; any photosite that has too much charge will be recorded as the highest number in the bit depth, by the ADC. Cameras rarely give you that real, initial raw data anymore, although many early digital cameras with raw did. Many cameras will multiply the original raw numbers and do additional clipping before writing the raw file. Then finally, the converter may cause clipping where there was none in the raw file.
And GFX. And Nikon Z. And Leica Q2M.
"Meter readings of the gray card should be adjusted as follows:
- For subjects of normal reflectance, increase the indicated exposure by 1/2 stop."
"ln use, the Gray Card is placed in the same illumination as the main subject, and angled slightly toward the primary light source. An exposure reading is then taken off the 18% gray surface of the Gray Card ."
"The gray side of the card reflects precisely 18% of the incident light, while the white side reflects 90%. The KODAK Gray Card is manufactured to extremely tight tolerances. Allowable deviation in reflectance is 1%, an insignificant variation for any photographic process."
Kodak, "How to Use KODAK Gray Card"
It would give you information on how you could vary exposure (or ISO setting) to get maximum SNR without unwanted highlight clipping. The recommended exposure for an ISO setting in a camera is just that exposure for which the default conversion parameters would create an image with normal, expected "lightness". Most cameras can take more exposure than that without highlight clipping in raw mode, and then you can pull down the lightness in the converter, and the tones should look the same as if you didn't give the extra exposure and pull the lightness down, but with less noise and less potential artifacts in deep shadows.
So, with your camera set to ISO 100, you may be able to expose for ISO 40 with the ISO 100 setting, which will give you 1.33 stops less read noise, and 0.67 stops less photon noise.
The question of how much extra exposure you can give depends on the subject matter. If it is a black cat on a black couch that isn't glossy, then you might be able to expose the ISO 100 setting for ISO 16 or 10, with a single exposure.
Some converters do unwanted strange non-linear things when you play with their lightness-related sliders, though, so you need to make sure your converter can handle it. It would be theoretically possible to make an app that takes raw files and scales down the values and puts them in a DNG, so that the converter itself doesn't have to do the lightness pull-down, but I don't think anyone has done so. It is a shame when the first lightness-related slider in a converter isn't a simple linear scaling slider for the raw input, and any shoulders or knees or gamma applied separately.
At any ISO, every stop you can increase exposure decreases read noise by 1 stop, and decreases photon noise by 1/2 stop, relative to signal. You usually only have that luxury in situations where you can do that at base ISO (or the base of a higher dual-conversion-gain range of ISOs) If you have a very-high-DR scene, then you also keep your shadows away from black, which means less of a chance that you get that magenta or green tint that some conversions cast in deep shadows.
