Amazing lens, incredible sharpness

Great Bustard wrote:

c_henry wrote:

Great Bustard wrote:

c_henry wrote:

Great Bustard wrote:

c_henry wrote:

So, if I had my 75mm f1.8 on my E-M5 and was using a light meter which told me to set the aperture to f1.8, what would I set it to?

I'm sure I can't speak for what you would do. I could tell you what I would do, if you like -- let me know.

Yes please, lets assume, to keep it simple, I'm aiming to get the exposure that the light meter is telling me to use.

In any case, neither here nor there, in terms of my post that you were responding to.

Actually it is.

That is, 75mm f/1.8 is 75mm f/1.8, not 150mm f/1.8. However, 75mm f/1.8 on mFT is equivalent to 150mm f/5.6 on FF, where by "equivalent to" I mean it has the same diagonal angle of view, the same DOF for a given perspective, framing, and display size, and projects the same total amount of light on the sensor for a given shutter speed, resulting in the same noise for equally efficient sensors.

Now, if I've guessed correctly, you don't care. No problem, but you did respond to my post, and, well...

Unfortunately not, I do care. So, back to my question. My 75mm f1.8 on my E-M5, if my light meter is saying to use f1.8 (@1/125th at ISO200 for instance) that would be the same on m43, APS-C, FF, medium format and large format for the same scene right?

See if my reply just above does not answer the questions for you then. If not, please feel free to ask for more details.

It does indeed.

Excellent!

So it's f1.8 no matter what the sensor size.

It's also 75mm no matter what the sensor size.

So the 75mm is the equivalent of a 150mm f1.8 on FF, except for DoF where you get more.

No. 150mm f/1.8 will also project 4x as much (2 stops more) light on the sensor for a given shutter speed, resulting in half (one stop less) then noise for equally efficient sensors.

Actually, it's yes. We've agreed f1.8 is f1.8 whatever the sensor size. If you want to go off talking about noise then, well, whatever floats your boat, but that's not what I was asking.

That's good to know. Appreciate the help.

Glad to help! So now you understand that 150mm f/1.8 on FF looks rather different than 75mm f/1.8 on mFT, whereas 150mm f/3.6 on FF looks very similar to 75mm f/1.8 on mFT (for a given shutter speed and sensor efficiency).

Again, not really relevant to my question, but appreciate you taking the time to miss the point.