So pulling up some details of the Panasonic Leica 100-400 f/4-6.3
100mm f/4, 200mm f/5.1, 300mm f/5.7, 400mm f/6.3
The FF equivalent f-numbers would be:
200mm f/8, 400mm f/10.2, 600mm f11.4, 800mm f/12.6
I don’t know where it crosses to f/4.5 but it’s likely for all overlapping focal lengths the Olympus will either be equal or ahead.
BTW, once we’re using equivalent f-numbers, we've already equalised the smaller sensor disadvantage so there will be NO IQ disadvantage vs a larger sensor except shooting at the base 2 stops of ISO's and even then it's largely a DR advantage that you need a scene with high enough DR to exploit. We're talking a super tele lens here so it's likely we won't be shooting at base so on a practical basis I'm not sure there will be any IQ disadvantage at all. Furthermore for scenes where you would be shooting at base ISO, there will be abundant light. Hardly an issue with m43 even with their “tiny sensors”. The only situation I can really think of where this might be an issue is the underside of a bird with white feathers on top but dark underneath shooting in the midday sun. But sure, if that's your regular scenario then choose something more appropriate.
Let’s not compare original manufacturers and third parties. There will be a premium on original manufacturer’s products no matter how it compares. Sigma’s mantra for their Art series have been excellent performance at a good price which comes at the cost of size and bulk. I’m not familiar enough with their Sports and Contemporary range to know their relative performance but suffice to say it ranks below their Art series for optical performance. The Olympus will likely gun for a different balance, we’ll just have to wait and see.
We don’t know the 150-400's wide open performance, performance at different focal lengths, it’s closest focusing capabilities among others.
Other potential benefits.
AF detection range favours the lens with the faster actual f-number (constant f/4.5 for the Olympus). Equivalent f-number, which describes total light and SNR doesn't matter here.
Optical zooming to achieve the AOV or 'reach' fills the frame with the subject much better than cropping. This improves the system’s ability to subject-recognise. Animal AF is already here. More precise animal eye AF can be achieved with optical zooming and better framing compared to cropping from a larger sensor.
Also as Pitachu mentions, it’s a constant aperture pro lens. It’s just a nicer experience dealing with a constant max aperture.
And is it any questions that the build and weather sealing of this lens would rival any lenses out there given weather sealing is kinda Olympus' thing.
We can also probably add stabilisation advantages since Olympus are arguably the leaders and sensor base IBIS favours the smaller sensors with less mass.
Let’s not judge it prematurely. Too many unknowns atm.
100mm f/4, 200mm f/5.1, 300mm f/5.7, 400mm f/6.3
The FF equivalent f-numbers would be:
200mm f/8, 400mm f/10.2, 600mm f11.4, 800mm f/12.6
I don’t know where it crosses to f/4.5 but it’s likely for all overlapping focal lengths the Olympus will either be equal or ahead.
BTW, once we’re using equivalent f-numbers, we've already equalised the smaller sensor disadvantage so there will be NO IQ disadvantage vs a larger sensor except shooting at the base 2 stops of ISO's and even then it's largely a DR advantage that you need a scene with high enough DR to exploit. We're talking a super tele lens here so it's likely we won't be shooting at base so on a practical basis I'm not sure there will be any IQ disadvantage at all. Furthermore for scenes where you would be shooting at base ISO, there will be abundant light. Hardly an issue with m43 even with their “tiny sensors”. The only situation I can really think of where this might be an issue is the underside of a bird with white feathers on top but dark underneath shooting in the midday sun. But sure, if that's your regular scenario then choose something more appropriate.
Let’s not compare original manufacturers and third parties. There will be a premium on original manufacturer’s products no matter how it compares. Sigma’s mantra for their Art series have been excellent performance at a good price which comes at the cost of size and bulk. I’m not familiar enough with their Sports and Contemporary range to know their relative performance but suffice to say it ranks below their Art series for optical performance. The Olympus will likely gun for a different balance, we’ll just have to wait and see.
We don’t know the 150-400's wide open performance, performance at different focal lengths, it’s closest focusing capabilities among others.
Other potential benefits.
AF detection range favours the lens with the faster actual f-number (constant f/4.5 for the Olympus). Equivalent f-number, which describes total light and SNR doesn't matter here.
Optical zooming to achieve the AOV or 'reach' fills the frame with the subject much better than cropping. This improves the system’s ability to subject-recognise. Animal AF is already here. More precise animal eye AF can be achieved with optical zooming and better framing compared to cropping from a larger sensor.
Also as Pitachu mentions, it’s a constant aperture pro lens. It’s just a nicer experience dealing with a constant max aperture.
And is it any questions that the build and weather sealing of this lens would rival any lenses out there given weather sealing is kinda Olympus' thing.
We can also probably add stabilisation advantages since Olympus are arguably the leaders and sensor base IBIS favours the smaller sensors with less mass.
Let’s not judge it prematurely. Too many unknowns atm.