Let's see if I understand this correctly. We can't trust the camera's auto exposure ability. I have heard it is "USELESS". So we'll shoot manually. That's the solution!!! But how do we know if our manual exposure is correct while we're shooting?
Oh wait, of course, I've got it! We'll check the histogram to be sure our manual exposure is correct. I guess it must be OK to trust the camera's determination of what the histogram should look like. Right?? Or maybe the camera's histogram can't be trusted as we've seen discussed here many times before ("We want a RAW histogram, not some crummy jpg rendered histogram that isn't accurate!!").
Hmmm. OK, NOW I've got it! We'll review the captured manually exposed image on the camera's LCD to be sure the exposure is correct. It must be OK to trust the camera's jpg rendering on that little 3" screen. Right?? or maybe we can't trust either the camera's jpg conversion from the RAW data or the LCD's ability to faithfully show the camera's converted jpg on the LCD !!
After all, if we can't trust the camera's auto exposure capability to generate a file we can use, why should we trust anything else that the camera does that might help us get to an exposure that we decide is correct?
Further variations on this theme:
Why trust the incident meter because......
Why trust either the camera's or my hand held spot meter because......
Why trust that my monitor's rendering of the image file because........
Brad
+1 !!!!
Basically what the AE does is that instead of you adjusting the exposure according to the reading the light meter in the camera (or hand-held meter) provides, the camera transfers the values automatically. So if you are using the camera's meter to adjust manual exposure, you are just complicated things unnecessarily.
So basically OP is saying his camera's light meter is not working properly.
For a true manual exposure you have to just shoot manual, and then check the exposures on your monitor or print them, then adjust accordingly. Trusting the histogram is not "pure manual exposure" just like Brad explained above. For me this is too slow, can not travel to the office between every exposure, and the auto exposure gives good enough result or even perfect result actually (+-1 EV tweaking latitude) 98% of the time, given the huge latitude modern cameras provide.
Just yesterday a colleague of mine showed a studio portrait which was underexposed 5 stops. The picture looked totally black unadjusted. With LR sliders it was possible to tweak the photo to be perfectly useable, nobody would notice anything unless pixel peeping. Camera was Nikon D4. So unless overexposing more than 1 stop just about anything AE provides is perfectly fine.