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<blockquote data-quote="Mike D90" data-source="post: 229922" data-attributes="member: 17556">I sure appreciate you taking time to try to help me understand. I am not having an issue understanding sensor size.&nbsp; I do definitely understand that.&nbsp; I also understand the the lenses focal lengths are the same&nbsp; between the lenses.I also understand the image that is projected onto the sensor is cropped by the smaller sensor due to it physically being smaller.What I cannot understand is why the need for a DX lens?&nbsp; If the sensor is going to crop an image then it wouldn't matter what size image circle is projected onto it.&nbsp; You have shown that in your images and explanations.A DX lens projects a smaller image circle onto the DX sensor, but that image is no different in ratio than the FX lens. It is simply cropped to the size of the DX sensor.&nbsp; So my misunderstanding is in building the DX lens to begin with.It makes no difference to the DX sensor which lens it gets its image from.&nbsp; It crops either one to the same size.So unless it is simply to cut the overall size of the lens and its weight down I see no need for a DX lens.</blockquote>

[QUOTE="Mike D90, post: 229922, member: 17556"] I sure appreciate you taking time to try to help me understand. I am not having an issue understanding sensor size. I do definitely understand that. I also understand the the lenses focal lengths are the same between the lenses. I also understand the image that is projected onto the sensor is cropped by the smaller sensor due to it physically being smaller. What I cannot understand is why the need for a DX lens? If the sensor is going to crop an image then it wouldn't matter what size image circle is projected onto it. You have shown that in your images and explanations. A DX lens projects a smaller image circle onto the DX sensor, but that image is no different in ratio than the FX lens. It is simply cropped to the size of the DX sensor. So my misunderstanding is in building the DX lens to begin with. It makes no difference to the DX sensor which lens it gets its image from. It crops either one to the same size. So unless it is simply to cut the overall size of the lens and its weight down I see no need for a DX lens. [/QUOTE]

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