My take on the RF 800mm f/11 DO IS STM for birds

Started 2 months ago | Discussions thread
J.K.T. Regular Member • Posts: 321
Re: Clarification.
2

MyDog Is Incharge wrote:

Crop mode, cropping, and a TC all reduce the effective aperture. There is no way to crop or use crop mode on an F8 image and still end up at F8.

When you crop, use a TC, or use crop mode, you are throwing away light. A TC throws away light and spreads the remaining light across the full sensor. Crop modes and cropping, crops away light and uses a smaller portion of the sensor.

I'm not convinced about that.

Whether you crop or not, your front element size is the same (d). When you crop, your focal length is the same as before (f) and the ratio f/d is not changed. Thus your aperture does not change. On the other hand, adding a TC changes the focal length and that changes the ratio and thus your aperture.

If you just crop, the diffraction does not change either ... relative to your pixel size. Relative to to the entire image it does, but calling that effective aperture is a bit of reach in my opinion. And if you use crop body with same number of pixels as the original, your diffraction is now larger relative to your pixels too. However, your description of the effective aperture seems a bit odd in that case as well.

Edit: Just a bit late...

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