Thanks for your coments.
Camera 1, the most compact, is a modified HIK camera, with a high-speed motorized varifocal lens. The varifocal lenses that are installed in these cameras work well, but they are very slow and the zoom takes a long time to approach objects and focus them, practically losing its usefulness except for focusing on very close objects. This modification allows you to use the zoom and focus in an agile way on the move without sacrificing quality, since the focus time is considerably reduced and the zoom is very fast.
I do the zoom and focus control with dedicated software, since, on the one hand, communication with the surface via RS485 or RS232 is not necessary and thus I don’t need to use an extra twisted pair of tether. And on the other hand, the dedicated software allows zoom and focus control directly with the ROV joystick, thus avoiding extra configurations.
The dedicated software allows you to view the IP camera, record, configure camera parameters, take photos, and control zoom and focus with the joystick. But if you prefer, it can be used only to control the zoom and focus with the joystick, using a secondary stream from the IP camera, with very low image quality, so as not to consume bandwidth and view the camera through qgroundcontrol. I prefer the first option, with a minimized screen of qgroundcontrol to see the navigation parameters.
For communication with surface I use FathomX up to 200m of tether, with more tether the data rate usually drops and is not enough for decent 4k streaming.
When the distance is greater, I use an ethernet conversion board with VDSL2 protocol. For example, the images that I have shared from the DAHUA 12 mp camera are transmitted live through 500m of 2x2x24awg copper umbilical, installed in a motorized spool that I have designed for the Marine Research Center of the University of Vigo CIM. (Attached photo and vídeo.)
Regarding the DAHUA vs HIK image quality, I prefer DAHUA 12 mp. In my ROV I have the previous version of the camera that I share in my previous post, and the image is excellent. But I think the new model is much better. You can see the quality of my ROV camera in the following links (in video settings select 4k).
With respect to larger and quality cameras, there is a wide variety such as blackmagic, cinema4k, Zcam and of course the ones you mention, but the size forces large casings and makes the ROVs not very maneuverable in difficult conditions such as sea currents, etc. But it is evident that everything depends on the use that you are going to give to the equipment.
In my latest design, I have tried not to give up image quality, integrating the DAHUA 12mp camera, in a compact ROV with great maneuverability and good response in strong currents, with a wide working range at great depth, thanks to a resistant and flexible tether of 500 m, thus avoiding fiber optics. On the other hand, I have incorporated UGPS, a 14.8V 36Ah battery customized for prolonged dives and a rotating arm with a servo of my own design. I think the result is a hard-working, maneuverable ROV with very interesting image quality.
I hope I have helped.