HD light metering -- need advice

Hi, I'm looking for a potentially better way to find the proper light value when shooting HD through a lens adapter/lens package. It seems like I'm missing something by following the f/stop my meter is telling me in accordance to the speed of my lens.

Currently, I'll look at my "target" f/stop according to the particular lens I'm using with a few other factors thrown in like adapter light loss, -3dB gain, light superiority, etc. Then, naturally, I'll choose a source that will provide that value.

However, it seems when I go from, for example, an f/1.4 50mm to an f/3.8 zoom, I'm needing to push way more light into the frame than my video monitor is letting on (not that I trust my monitor completely). Let's say I'm over-correcting for my rig's light loss by 2 stops, for my key I would look for about an f2.8 on my meter with my 50mm (f/1.4) wide open. But then on my zoom (f/3.8) I would need almost an f8? That's almost 3 stops from one lens to the next which seems a little extreme. Again, I know you can't trust the monitor, but it doesn't look that much darker to me when switching lenses in the same lighting conditions.

There maybe other factors in there that I'm not considering or maybe I'm getting this system confused with a t-stop exposure. The settings on my camera aren't changing at all and of course I shoot wide open on the lens themselves all the time.

Until I can afford to buy a waveform, this is my practice. I 'm sure there are plenty of people on here who can steer me the right way.

Thanks.

Chris