Why is the Daylight White Balance setting of my Canon 450D showing in Lightroom as 4900K instead of the 5500K it should be? The images shot in shade have a distinct blue cast. Does the lens affect WB? I'm using a Tamron 18-270mm
'Daylight' white balance is for shooting under direct sunlight during mid-morning through mid-afternoon. The diffused indirect sunlight that illuminates subjects in the shade on a sunny day or even out in the open when the sun is obscured by clouds will have a much cooler cast/higher color temperature than subjects directly lit by sunlight. You should not use 'Daylight" WB for subjects not being directly lit by sunlight. Instead use 'Cloudy' (≈6000K) or 'Shade' (≈7000K) WB.
Most Canon cameras seem to put 'Daylight' WB at around 5200K in terms of color temperature. Other camera makers may use anywhere from around 5000K to 5600K. All are more or less correct because the temperature of direct sunlight varies during the daylight hours. It will be cooler (higher color temperature) at noon than at 9 a.m. or 3 p.m. Noon on the equator will have a higher color temperature than noon at a high northern or low southern latitude when the sun will still be at a lower angle in the sky compared to locations closer to the equator. Weather and atmospheric conditions will also have an effect on the exact color temperature of direct sunlight. The amount of water vapor and the color and concentrations of particulates in the air can affect the color temperature of sunlight. During spring when a lot pollen is flying around in the air where I live using 'Daylight" WB can give a very yellow/green tint to photos shot under sunlight!
- Color temperature is an adjustment along only one axis on the 360° color wheel that includes all white balance adjustments. The low end of the Kelvin scale is biased towards purple (to make up for orange light) about one third of the way between pure blue and pure red and the high end is biased towards orange (to compensate for very bright, cool light) about halfway between pure red and pure green. My Canon cameras also introduce a bit of blue bias along the Blue<--->Yellow axis and a bit of bias along the Green<--->Magenta axis when set to 'Daylight'. Both 'Cloudy' and 'Fluorescent', for example, use a color temperature of about 6000K, but the fluorescent setting also includes quite a bit of bias towards magenta to offset the green cast from fluorescent lights.
- Most of the time Canon's 'Auto' WB will do a good job of selecting the correct color temperature and WB when outdoors during the day and will usually pick up any additional color casts that may be affecting the scene and will compensate for them as well. If I need to precisely control WB then I'll set the color temperature (Kelvin) and WB correction to a specific value for a given situation, or even use a 'Custom WB' from a photo of a neutral gray target taken under the same lighting as that under which I will be shooting.
The lens will only affect WB if it has a distinct color tint. If you can't see any when using that lens vs. your others in other situations, then no, the lens you're using isn't having an effect. It's that you chose the wrong WB setting for the situation you were shooting (i.e., using sunshine for shade shooting, instead of shade).
Another alternative to controlling WB precisely is to shoot RAW and adjust WB in post. The WB setting in the camera is really only meaningful if you're shooting JPEG.