Please clarify extender magnification for me...

Started Nov 29, 2012 | Discussions thread
Dave Seeley
Contributing MemberPosts: 716
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Re: Please clarify extender magnification for me...
In reply to ammac12, Nov 30, 2012

ammac12 wrote:

So, does having a field f view of 448mm lens mean I am "zoomed" in to 448mm? Or am I zoomed to 280mm, with a 448mm fov?

Others, please chime in if you think I'm wrong, but I believe...

Technically, the 1.6 crop factor just means that the camera's sensor is already a crop of the image that is projected through the lens... so it's like you had a projector and a screen in your living room, but the image you are projecting is larger than the screen.  In the Camera, the screen/sensor is all you can see.  (The up side is that the edges of the lens, traditionally the weakest optically, are never utilized in a crop camera.)

The extender changes the focal distance, so it would be like moving your projector backward in you living room, to expand the picture on the screen.  Your camera still only see's the portion on the screen...so it is effectively a further crop.  It is also less light that makes it to the screen/sensor, so that is why you take a hit for aperture.  Same in the analogy of moving the projector backward in your living room.  The picture dims with relative size.

I believe that both are ultimately resolving a reduced area of your lens.

so your zoomed to 200, you are using only the portion of the resolved image coming through your lens that is equivalent to a 448mm lens.

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