01-07-2011, 04:40 PM
[quote name='genotypewriter' timestamp='1294362096' post='5371']
Actually the difference is roughly 2 stops because the area of a FT sensor is 17.3x13=224.9 and the area of a FF sensor is 36x24=864. So 864/224.9 = 3.84 ~= 2 stops.
[/quote]
I have included the F stop advantage of the 300mm 2,8 over the Canon 600mm 4.
These lenses have exactly the same (fstop = focal length / diameter) diameter.
So it is possible to build lenses with better F stops for smaller sensors.
But you're right with your statements below.
I would say that it is all a matter of weight you want to carry with and how high your requirements to the camera systems are.
The Leica D-Summilux you mentioned has really high resolution. It might be right that a 50mm 2,8 is better, but the difference is not that great.
[quote name='genotypewriter' timestamp='1294362096' post='5371']
E.g. A 70-200 2.8 lens on a FF is like a 35-100 f/1.4 on FT but there's no such thing on FT. As another example, the Leica D-Summilux 25mm f/1.4 for FT is like a 50mm f/1.4 FF lens stopped down to f/2.8. A 50 2.8 on FF would be sharper and be smaller and cheaper too.
So at the end of the day FT (and small sensors in general) need faster lenses and higher resolution sensors than FF cameras to match them. Making a lens fast and high in resolution are very conflicting objectives.
In comparison, just making an image circle bigger is not that difficult. For example the [url="http://www.bhphotovideo.com/c/product/36862-GREY/Nikon_1309_105mm_f_5_6_Nikkor_W_Lens.html"]Nikor-W 105 f/5.6 lens[/url] has an image circle that is 31x the area of a FT image circle but it's still a f/5.6. It weighs only 185g and costs $350... but on its native format (6x9) it only needs to resolve 22 lp/mm to match that 12-60's 12MP resolution. And it does that while giving the DOF of 42mm f/2.2 lens on FF.
GTW
[/quote]
Actually the difference is roughly 2 stops because the area of a FT sensor is 17.3x13=224.9 and the area of a FF sensor is 36x24=864. So 864/224.9 = 3.84 ~= 2 stops.
[/quote]
I have included the F stop advantage of the 300mm 2,8 over the Canon 600mm 4.
These lenses have exactly the same (fstop = focal length / diameter) diameter.
So it is possible to build lenses with better F stops for smaller sensors.
But you're right with your statements below.
I would say that it is all a matter of weight you want to carry with and how high your requirements to the camera systems are.
The Leica D-Summilux you mentioned has really high resolution. It might be right that a 50mm 2,8 is better, but the difference is not that great.
[quote name='genotypewriter' timestamp='1294362096' post='5371']
E.g. A 70-200 2.8 lens on a FF is like a 35-100 f/1.4 on FT but there's no such thing on FT. As another example, the Leica D-Summilux 25mm f/1.4 for FT is like a 50mm f/1.4 FF lens stopped down to f/2.8. A 50 2.8 on FF would be sharper and be smaller and cheaper too.
So at the end of the day FT (and small sensors in general) need faster lenses and higher resolution sensors than FF cameras to match them. Making a lens fast and high in resolution are very conflicting objectives.
In comparison, just making an image circle bigger is not that difficult. For example the [url="http://www.bhphotovideo.com/c/product/36862-GREY/Nikon_1309_105mm_f_5_6_Nikkor_W_Lens.html"]Nikor-W 105 f/5.6 lens[/url] has an image circle that is 31x the area of a FT image circle but it's still a f/5.6. It weighs only 185g and costs $350... but on its native format (6x9) it only needs to resolve 22 lp/mm to match that 12-60's 12MP resolution. And it does that while giving the DOF of 42mm f/2.2 lens on FF.
GTW
[/quote]