[Brightcolours]

I've done it in the past, but in my case (Nikon D100 + AFS 300 f/4) the resulting f/8 max. aperture was barely enough for the AF to work - in other words, no chances of getting BIF. One of the points of thxbb12 is that with f/4 it's reasonable to expect a very good AF speed.

Yep, of course you get an AF advantage. And an IS advantage on your case. And probably a sharpness advantage. But talking about lens equivalency is not talking about how this Olympus lens would be worse (it is most probably a very fine lens and will not be "worse" than equivalents, in many cases actually better). Yet whenever one mentions what the lens is equivalent to (in focal length and f-value) in FF 135 format terms, there are always people who take it that way. There probably is a term for that.

As I asked for some days ago   knowing the size and weight of the new lens is fundamental to place this discussion in context.

Not really. It still is equivalent to 600mm f8 on 135 format, even if it is small and light. Also if it is big and heavy. Lenses being equivalent on different formats in focal length and f-value terms says nothing about the particular lenses' advantages and disadvantages. It is not about "better" or "worse", just about similar properties concerning FoV and DoF. And when one for whatever reason feels a need to have similar exposure times, one just has to dial in an equivalent ISO setting.

[frank]

Size comparison:

 

[thxbb12]

Size comparison:

 

 

That 300mm is absurdly long. It's longer than the Pentax DA 300 f/4 which is a FF design!

I'm still waiting for Olympus to release a compact prime UWA in the 15-18mm range (FF equiv). Oh well...

[stoppingdown]

That 300mm is absurdly long. It's longer than the Pentax DA 300 f/4 which is a FF design!

I'm still waiting for Olympus to release a compact prime UWA in the 15-18mm range (FF equiv). Oh well...

 

Actually it is - just 4cm shorter than my Nikkor AF-S 300 f/4   , FF of course. Those 4cm are roughly the size of the TC 14 teleconverter, which gives the same angle of view on an APS-C body. Perhaps there's an advantage in terms of weight...

 

Perhaps it's the 40-150 zoom to be more interesting...

[Brightcolours]

Of course it is long, it is a 300mm prime.... Why would it have to be shorter than an FF design? The Pentax DA* 300mm f4 is an APS-C design (DA), and is shorter only if one does not count the mirror box size. The Nikkor 300mm f4 is very big, count in the mirror box size and the lens is more than 6cm longer. 

 

Where the Oly may have an advantage is weight, but with tele primes the smaller image circle needed for the smaller sensor only really counts for back elements, not so much for front elements.

[thxbb12]

It indeed appears the DA* 300 works just fine on FF:

• http://www.dpreview.com/forums/post/28774234
  
• http://ricehigh.blogspot.com/2009/10/com...-full.html
  

[stoppingdown]

Of course it is long, it is a 300mm prime.... Why would it have to be shorter than an FF design? The Pentax DA* 300mm f4 is an APS-C design (DA), and is shorter only if one does not count the mirror box size. The Nikkor 300mm f4 is very big, count in the mirror box size and the lens is more than 6cm longer. 

 

For instance, there are patents which claim to save a few centimetres more... But in the end weight is what I'm more interested and there could be advances in materials, rather than in optics.

[Brightcolours]

For instance, there are patents which claim to save a few centimetres more... But in the end weight is what I'm more interested and there could be advances in materials, rather than in optics.

Of course, Canon has used DO elements in two lenses (70-300 DO and 400mm f4 DO). Both are indeed MUCH shorter than their non-DO counterparts (in fact, the Canon 400mm f4 is shorter than the Nikkor 300mm f4). But the Oly does not use any DO element, so why would it be shorter? That was my point.

[stoppingdown]

Correct, in fact I was talking in general, for when we see the announce of a new lens of which we don't know much about.