[thxbb12]

Sensor size is NOT irrelevant. What is irrelevant is what you are saying (that "f/4" meters the same").

A lens does not meter. Would you give ISO 100 film and ISO 640 film the same exposure duration? No?

Why is that?

Maybe because they have different sensitivities?

Ok. So, why are you adamant in exposing sensors with different sensitivities the same? Sensors with smaller pixel/sensel/photo sensitive diode pitch have different sensitivities).

 

Point is: ISO is NOT what it used to be with film. One does not set a meter to meter for a certain film sensitivity anymore. Now one simply changes the ISO setting for whatever a certain image requires, and ISO is not about sensor sensitivity.

So don't bring in "metering at f4" as argument, it basically is a non-argument. Set the cameras to equivalent ISO settings and "f4" will NOT give similar exposure results. Nor similar DOF results.

You are saying: the light hitting the MFT sensor is LESS than the light hitting the FF sensor. That is because the MFT sensor is so much smaller (4x less light). Also: suppose the sensors have similar amount of pixels/sensels/photo sensitive diodes. Then the MFT sensels collect 4x less light energy, due to their smaller size. So, both on image level, and on pixel level, the MFT sensor will collect less light at f4.

No, exposure is not similar at all. See above. (Less light per image. Less light per pixel. Difference in sensor sensitivity. You just do not realize that because you misunderstand what "ISO" means in the digital age.)

No, it does not. Get that ISO 100 on MFT does NOT mean the same as ISO 100 on FF. The amplification to the signal will NOT be the same. Just like with film, where a bigger grain gives a higher sensitivity, a bigger sensel will collect more light too. So, would you say that ISO 100 film in a 4/3rds size film camera and an ISO 400 film in a FF film camera get equal exposure, with f/4?

I think you will not. Yet that is what you are saying about MFT vs FF sensors. 

 

With film, ISO says something about sensitivity. With digital, it does not. So, stop looking at ISO as a set thing. That is not valid anymore. With digital, ISO is just about getting more or less similar results REGARDLESS of sensitivity, by applying different amounts of amplification and/or sensor voltage for different sensors.

That is nonsense.... Why can you handhold 300mm f4 at ISO 400 and not 600mm f8 at ISO 800? Makes no sense.... One REALLY can change ISO settings to whatever one needs. Or even have the camera do it itself with Auto ISO setting.

 

There is no reason what so ever to set different cameras at the same ISO setting number.

 

Wooow, relax, no need to be so agitated.

 

All I'm saying is extremely simple:

An f/4 lens on MFT will meter the same as an f/4 lens on FF. That's what I meant when I said "sensor size is irrelevant". Nothing more, nothing less.

I this context, if you set a D800 with a f/4 lens (no matter the focal - that's not the point here) at ISO 400 and 1/200 for instance, you will get the same exposure as with an E-M1 with a f/4 lens at ISO 400 and 1/200.

I don't care whether ISO 400 on FF is roughly 1-2/3 stop better than on MFT. That's not the point. I was just talking about exposure.

I used to own a D800 and I switched to MFT, so I perfectly know the tradeoffs I made by doing so. To me, the IQ difference *in real life* is not significant.

 

Now, regarding the 600mm equivalent lens.  Yes, you can sure use the combos you mentioned. However, the 300mm f/4 Oly lens will probably have much better IQ than any of the solutions you suggest. Also, as you mentioned, there is no 600mm f/8 lens in existence in the FF world (and if it did, it would lead to AF issues anyway).

Bottom line: to reach 600mm on FF, you need to carry something huge and heavy. That's the whole point of my previous replies.