It appears that neither the Sony 55-210 mm f/4.5-6.3 nor the Canon EF-S 55–250mm f/4–5.6 reports the actual focal length to the camera: both cameras' metadata show the lens but report the focal length as the minimum zoom.
I took pictures of the full moon and got some odd results, looking at the exposures closely. In particular, the size of the subject changed in the frame, which makes me think the zoom was not staying where I put it.
Could someone help me reverse-engineer the focal lengths actually used? Besides better comparing the two systems, I wonder if the longest zoom on the Canon in giving more chromatic aberration and less contrast, since even after reconciling the exposure difference I have effects I can't explain. So knowing the settings used will be helpful.
Exposure 1: Sony α-6000 which has a crop factor of 1.5 (15.6mm tall tensor) and a vertical resolution of 4000 pixels. Image of full moon is 137 pixels. I had intended to zoom the lens to 210mm.
Exposure 2: Canon 70D which has a crop factor of 1.6 (15mm tall sensor) and vertical resolution of 3648 pixels. The full moon is 135 or 136 pixels.
Exposure 3: Canon 70D, full moon is only 125 pixels tall. This makes me think that the setting changed between exposures, obviously.
The shots were taken on 2015-August-1 just after 1:30 AM local time, just north of Dallas Texas.
Could someone give me a hand with this photometry problem?