Originally posted by az1895 It CANT ! It doesn't know what lens your using ! Without a link to know the A value its imposible. It doent know if wide open is a f1.2 or a f3.5. There is NO direct info through the contacts to the camera meter. Only A series lenses are fully compatible in Av , M , or Tv modes. The M42 , K , and M model lenses aren't fully compatible. Uasble...Yes. But the camera wont give you an Aperature and shutter value. Your limited to M mode or Av mode with an exposure time based on the lense stopped down. I know its confusing to me too ! here is an example... Im in M mode and I set my lens to f/11... if I use the green button to stop down and do a meter value and the camera says 1/125 sec , that gives me a starting point. Now I mentally know that my lens stopped down to the set value of f/11 on the lens. Hence...My lens says f11 and the meter stopped down reads 125sec.....Now that makes sense to me , but its not all in the camera on the old lenses.....there isn't full compatability.
I think that when JohnnyXD says he wants a "exposure value", he means he just wants an "over/under" indication - like what a light meter gives you. When you do DOF preview, the camera stops the lens down, the same way as it does when you push the green button. If it can compute and set an appropriate shutter speed when you push the green button, then it can also display an over/under exposure reading based on the current shutter speed, and by how many stops when you do DOF preview.
Want proof? My old K200D ( also a mid-range Pentax DSLR ) does it just fine, and if you have the camera set to spot metering, you can trigger DOF preview and pan around your scene and see, for example, that the white flower over there is 2 stops over, the shadow over there is 1.5 stops under, and the gray card at my feet is at "0". AFAIK, the K7 does this, and probably the K5 as well.
Turning off the meter during DOF preview ( and during live view ) was a bit of a prickish thing to do IMHO. Had I known there was no way to meter with a manual lens, I would have had second thoughts about purchasing this camera. Since all previous cameras supported this, I just assumed this one would as well.
Cheers, Rick