Sony a7SIII Help Manual page 358

If you connect this camera to a TV using an HDMI cable, available menu items are limited.
Only TVs that support "BRAVIA" Sync can provide SYNC MENU operations. For details, refer to the operating
instructions supplied with the TV.
If the product performs unwanted operations in response to the TV remote control when the product is connected to
another manufacturer's TV using an HDMI connection, select MENU →
FOR HDMI] → [Off].
Hint
This product is compatible with the PhotoTV HD standard. When you connect a Sony PhotoTV HD-compatible device using an
HDMI cable (sold separately) or the USB cable, the TV becomes set to an image quality suitable for viewing still images, and a
whole new world of photos can be enjoyed in breathtakingly high quality.
The PhotoTV HD allows for a highly-detailed, photo-like expression of subtle textures and colors.
Note
Do not connect this product and another device using the output terminals of both. Doing so may cause a malfunction.
Some devices may not work properly when connected to this product. For example, they may not output video or audio.
Use an HDMI cable with the HDMI logo or a genuine Sony cable.
When [Time Code Output] is set to [On], the image may not be output properly to the TV or recording device. In such cases, set
[Time Code Output] to [Off].
If images do not appear on the TV screen properly, select MENU →
→ [2160p], [1080p] or [1080i] according to the TV to be connected.
During HDMI output, when you switch the movie from 4K to HD image quality or vice-versa, or change the movie to a different
frame rate or different color mode, the screen may become dark. This is not a malfunction.
5-021-326-11(1) Copyright 2020 Sony Corporation
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(Setup) → [External Output] → [CTRL
(Setup) → [External Output] → [ HDMI Resolution]