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TeamSpeed wrote:
If you have to crop and THEN resize the image back up, an optical extender is almost always superior to a digital upsampling.
Yep. How much better will depend on a lot of factors, though.
If you don't have to resize the image up for a large print or whatever, then it could be a wash either way, depending on the light levels.
The TC will still be better, regardless of the light.
Since the TC adds a stop, you will probably change ISO to be higher to compensate, and end up with a 1 stop noisier image.
Cropping costs the same stop of light, but you lose the resolution. For example, a photo of a scene at 300mm f/4 1/500 ISO 400 cropped to the same framing as an uncropped photo of the same scene at 420mm f/5.6 1/500 ISO 800 will be made with the same amount of light, and thus the same noise with respect to the light. However, the ISO 800 photo will be slightly *less* noisy than the ISO 400 because higher ISO settings on Canon sensors add in less electronic noise than lower ISO settings. Furthermore, because the photo with the TC will capture more detail, when noise filtering is applied to it to match the detail of the cropped photo, that will only serve to extend the noise advantage of using the TC.
The exception, of course, is if the aberrations in the TC degrade the photo more than the extra pixels help the photo. In this case, the bare lens and cropping will be superior. In addition, the TC made degrade the AF speed/accuracy of the system, and even being a little out of focus will do more harm than the extra pixels will do good.
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