Re: Sigma 500mm f/5.6 DG DN OS Sports Image Thread
RikWriter wrote: arbitrage wrote:
This lens looks promising. I'm keeping it on my short list along with 300GM and Z8/600PF.
Like Chris I would never use a TC on an f/5.6 lens. I don't even like them on Sony's native $12K prime lenses which start at 2.8 and 4 so no way I'll be happy with one on a Sigma 5.6 lens.
Huh. I can't understand that mindset.
The gap between a TC and cropping is smaller than you think...
For a perfect lens we have:
angular resolution = 1.22 λ/D
D = focal length / f-stop
combine the above two formulas and we get:
angular resolution = 1.22 * λ* f-stop / focal length
Remove the constants (lambda in our case is visible light frequencies), and we see the relationship:
angular resolution ~= f-stop / focal length
For the TC case, using a 24mm height FF sensor and 2x TC with a 300/2.8 lens:
angular resolution ~= f/5.6 / 600mm = 0.009
And for the case of cropping, we only use half the sensor height:
angular resolution ~= f/2.8 / 300mm = 0.009
Notice that the angular resolution provided to the sensor by the lens in both cases is the same.... which means that the smallest detail you can resolve through using the TC and cropping is the same!
However in the real world...
The sensor is not infinite resolution, using a TC gives a low res sensor an easier time compared to cropping.
The lens is not perfect, which reduces the resolution requirement on the sensor
The TC is not perfect, using a TC reduces resolution as a result
Particularly if you use a high res sensor, its very possible that you get a better image from cropping compared to using a TC.
edit:
autofocus and tracking also works better without the TC, the brighter the lens the better for AF.
Re: Sigma 500mm f/5.6 DG DN OS Sports Image Thread
RikWriter wrote: arbitrage wrote:
This lens looks promising. I'm keeping it on my short list along with 300GM and Z8/600PF.
Like Chris I would never use a TC on an f/5.6 lens. I don't even like them on Sony's native $12K prime lenses which start at 2.8 and 4 so no way I'll be happy with one on a Sigma 5.6 lens.
Huh. I can't understand that mindset.
The gap between a TC and cropping is smaller than you think...
For a perfect lens we have:
angular resolution = 1.22 λ/D
D = focal length / f-stop
combine the above two formulas and we get:
angular resolution = 1.22 * λ* f-stop / focal length
Remove the constants (lambda in our case is visible light frequencies), and we see the relationship:
angular resolution ~= f-stop / focal length
For the TC case, using a 24mm height FF sensor and 2x TC with a 300/2.8 lens:
angular resolution ~= f/5.6 / 600mm = 0.009
And for the case of cropping, we only use half the sensor height:
angular resolution ~= f/2.8 / 300mm = 0.009
Notice that the angular resolution provided to the sensor by the lens in both cases is the same.... which means that the smallest detail you can resolve through using the TC and cropping is the same!
However in the real world...
The sensor is not infinite resolution, using a TC gives a low res sensor an easier time compared to cropping.
The lens is not perfect, which reduces the resolution requirement on the sensor
The TC is not perfect, using a TC reduces resolution as a result
Particularly if you use a high res sensor, its very possible that you get a better image from cropping compared to using a TC.
edit:
autofocus and tracking also works better without the TC.
Re: Sigma 500mm f/5.6 DG DN OS Sports Image Thread
RikWriter wrote: arbitrage wrote:
This lens looks promising. I'm keeping it on my short list along with 300GM and Z8/600PF.
Like Chris I would never use a TC on an f/5.6 lens. I don't even like them on Sony's native $12K prime lenses which start at 2.8 and 4 so no way I'll be happy with one on a Sigma 5.6 lens.
Huh. I can't understand that mindset.
The gap between a TC and cropping is smaller than you think...
For a perfect lens we have:
angular resolution = 1.22 λ/D
D = focal length / f-stop
combine the above two formulas and we get:
angular resolution = 1.22 * λ* f-stop / focal length
Remove the constants (lambda in our case is visible light frequencies), and we see the relationship:
angular resolution ~= f-stop / focal length
For the TC case, using a 24mm height FF sensor and 2x TC with a 300/2.8 lens:
angular resolution ~= f/5.6 / 600mm = 0.009
And for the case of cropping, we only use half the sensor height:
angular resolution ~= f/2.8 / 300mm = 0.009
Notice that the angular resolution provided to the sensor by the lens in both cases is the same.... which means that the smallest detail you can resolve through using the TC and cropping is the same!
However in the real world...
The sensor is not infinite resolution, using a TC gives a low res sensor an easier time compared to cropping.
The lens is not perfect, which reduces the resolution requirement on the sensor
The TC is not perfect, using a TC reduces resolution as a result
Particularly if you use a high res sensor, its very possible that you get a better image from cropping compared to using a TC.
Mar 13, 2024 at 01:48 AM
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