[thxbb12]

Well, it's all just theoretical. In practice it's simply not the case as Klaus has shown in the article. To quote what I wrote in the comment section of the article:

 

"the most important aspect is that most lenses in APS-C and MFT land don't have FF equivalent, hence the size gain: Fuji 18 f2, Pana 14 f2.5, Oly 12 f4, Oly 17 f1.8, Oly 25 f1.8, Oly 45 f1.8, Pany 12-32 f3.5-5.6, Oly 9-18 f4-5.6, Fuji 18-55 f2.8-4, Fuji 14 f2.8, etc. It would be perfectly possible to have similarly small FF lenses if there were such equivalent lenses (28 f3, 28 f5, 24 f8, etc.) but I highly doubt it will ever happen. From a marketing point of view, manufacturers would have a tough time convincing customers a 24-64 f7-12 lens or a 24 f8 is sexy despite the size gain... So, if one doesn't mind the loss in DOF control and is happy with the smaller sensor IQ, then smaller systems make a lot of sense. Even with MFT, from a pure IQ point of view, we've reach the "good enough quality" a long time ago already."

[Brightcolours]

There is no reason to get a big sensor and very small aperture lenses. The single big advantage of FF sensors is... possible more shallow DOF. See the equivalence theory.

 

So, if you are not in need of the very shallow DOF options, no need for a big sensor. Simple as that...

 

Equivalence is not about one system being better or worse than others, it is just about understanding the relationship of sensor size to lens attributes. And, understanding what is needed for which task.

[Klaus]

Well, the listed examples show that such equivalent FF lenses exist - although to be fair few slow lenses are professional grade.

A Canon 300mm f/4 + 2x is roughly similar to the Olympus 300mm f/4. If you optimize the combo you could achieve a similar quality I guess. But then who would buy a 600mm f/8 USM L IS for a DSLR ? It would make more sense for the Sony A7x.

 

BTW, the game is also possible the other way round ... 

http://www.metabones.com/products/detail...EF-m43-BT3

[huffy49]

 

Math is on my side.

Way back in the late '60s my physics professor demonstrated mathematically that depth of field depended only on the relative image size and the focal stop in use.

[Brightcolours]

 

Way back in the late '60s my physics professor demonstrated mathematically that depth of field depended only on the relative image size and the focal stop in use.

And subject distance. And viewing distance. But the last one does change the image size.