The MC20 (2XTC) Two Stop Exposure Loss “Fallacy” for Wildlife Photographers. It Can be a 2 Stop Gain

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drj3 Veteran Member • Posts: 9,068
The MC20 (2XTC) Two Stop Exposure Loss “Fallacy” for Wildlife Photographers. It Can be a 2 Stop Gain
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When I attach the MC20 TC to my 300mm f4 lens, the camera reports an aperture of f8 and raises the ISO by two stops compared to the lens without the TC. If I photographed a stationary bird at 1/800, f4, and ISO 200 with the 300mm, the camera setting for the same bird would be 1/800, f8 and ISO 800 with the MC20.

There is an apparent 2 stop loss. However, the bird in the 300mm image would need to be cropped to ½ its height and width to be equivalent to the 600mm image. The image of the bird using the 300mm without the MC20 would have the same amount of light as the 600mm bird image, but have ¼ the number of pixels and thus less resolution and color information while having no exposure advantage.

The 300mm f4 cropped image is the equivalent of using the 300mm lens on an 8.65x6.5mm 5MP sensor or equivalent to the 600mm f8 lens on the mFTs camera.

A lens without a TC has an IQ advantage, if you can get closer to the target. Of course, if you can get closer to the target, then you should not be using a TC. If you cannot get closer to the target, then the MC20+300mm f4 image should always be better than the 300mm f4 cropped image taken from the same location.

However, the 600mm f8 lens can actually have a 2 stop IQ advantage over the 300mm lens without the TC. If I lower the shutter speed to 1/200 for the 600mm f8 lens in the above example giving an ISO of 200 (the base ISO) then I will have with four times the amount of light on the target compared to the cropped 300mm image at ISO 200.

Anytime you can have the same ISO for the MC20+300mm vs the 300mm cropped image, the MC20+300mm will have a 2 stop advantage.

When photographing a moving target, you cannot normally lower the shutter speed to increase the amount of light on the target. However, the MC20+300mm image will still have the same amount of light on the target and 4 times as many pixels on the target as the cropped 300mm f4 image, so the image with the MC20 should still give better IQ.

However, if you photograph a target twice as far away as those you photograph with the 300mm, you cannot expect the MC20 to give equivalent IQ, since you do now loose 2 stops relative to the 300mm and you have the same number of pixels on the target.

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drj3

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