[dallas kruse] “Sony a7s ii….shooting some performance shots tomorrow where a LOT of colored lighting is going to be used. Dancing lights. Fog. Effects. Etc….I’m wondering if I should shoot in 4k or stick to 1080?…I know the advantages of being able to zoom or crop with 4k footage but wondering if it’s going to make a HUGE difference in output quality?”
I would NOT shoot 1080p on a camera designed primarily for 4k, unless meticulous testing shows that camera’s 1080p output is good in all your conditions. This is totally separate from the issue of 1080p vs 4k on a camera designed for 1080p, like the 5D Mark III.
E.g, my 5D3 produces good quality 1080p, esp. in low light. My A7RII (in 4k Super35 crop mode) does at least one stop better in low light but both are very good. In that comparison the issues might be logistical handling of the data on a long program, don’t have to transcode 1080p whereas 4k requires transcoding to proxy for good editing performance, etc.
However the 1080p vs 4k decision can be totally different if the camera is designed mainly for 4k. A lot of such cameras don’t produce very good quality 1080p. To get a 4k sensor to produce this, the image must be pixel binned or resampled or line scanned or heavily cropped or something else. This often degrades the image quality dramatically, especially in low light or adverse conditions.
Another issue is 4k cameras may force you to a non-ideal codec when used in 1080p, such as AVCHD. IMO that alone warrants staying with 4k. In FCPX AVCHD can be a little tricky to handle, and I usually rewrap it with EditReady before importing.
I don’t remember the A7SII behavior on 1080p — you’ll have to research and test that. So the issue is not combining 1080p and 4k on the timeline — that is easy for FCPX. However in proxy mode 4k material is 1080p, but 1080p material is only 960 x 540, maybe not enough for some editing decisions. Since FCPX’s proxy mode is global — all files are displayed as proxy or none are — when using mixed 4k and 1080p material you might be forced to use optimized media, not proxy. This allows display of mixed 4k and 1080p while retaining good editing performance. However this increases disk space by about 6x over H264. IMO it’s easier to just use all 4k and transcode to proxy.
The main issue is whether a camera designed for 4k will produce a compromised image if set to 1080p mode, as compared with a pure 1080p camera. If there is the slightest chance of this it’s better to shoot in 4k. If your particular 4k camera produces excellent, non-compromised 1080p (inc’l low light, no aliasing, equal dynamic range, good codec and bit rate for that resolution, etc) freedom from aliasing, then the issue is storage space and transcoding to proxy.