A7S ii - how far can I zoom in with 4K on 1080p time line?

jcs said:
In Premiere, if one drops 3840x2160 footage into a 1920x1080 sequence, without setting Scale to Framesize, the result with be a 1920x1080 center crop of the 3840x2160 frame. Zoom in this case is 100%, which is the same view as a 200% zoom if putting UHD in a UHD sequence (not 400%). The reason it's not 400% is the scale/zoom factor is applied to both width and height. In order to get 1920 into 3840, the zoom/scale is 2x or 200%. This same zoom/scale is also applied to height at the same time. So even though the total resolution increase is 4x for UHD vs. HD, the zoom/scale is applied equally to width and height, and thus the zoom/scale factor is 200% (2x if going up, and 1/4 or 25% if going down).
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Excellent, as I was looking at the picture from Blafarm what you described is exactly what I was thinking was happening to get to the 200%. Thanks to everyone for the insight, this forum rocks!
 
There might be a lot more compression in those a7s files when zoomed into though, macroblocks and the like.
 
It seems different software options use different terminology: Adobe uses linear measures to calculate scale (so, 50% and 200%), Avid uses area measures (hence 25% and 400%). Just know what your software is doing and ride along.
 
blafarm said:
Understood. And the answer is 400% (25% of UHD)-- although you can likely go a little bit further without seeing meaningful image degradation.
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UHD has 4x the number of pixels but is only 2x larger in width and height, 3820 x 2160 v 1920 x 1080. If you zoom 200% percent you will have 1 recorded pixel for every final pixel, using a 1920 x 1080 portion of the UHD recording. If you did a 400% you would only have 1 recorded pixel for every 4 final pixelsor would be using a 960 x 540 portion of the original UHD recording. You may be able to go a little beyond 200% but it will start getting soft after all even at 200% it will have a slight quality loss since you are loosing the benifits of super sampling when down scaling an UHD image to HD.

Personally I would not go beyong 200% unless absolutely necessary.
 
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