Camera won't go below F3.9 unless I disable AGC (video)? (f2.8 lens)

Teagan wrote on 8/28/2020, 10:20 AM

Ok so I decided to learn more about my camera (Panasonic AG-CX350), which is probably the wrong kind (broadcast camera) for what I do but some of the features like HLG (rec 2020) and V-Log (rec 709) and 20x optical zoom are really great sometimes. It also can record 10 bit HEVC 4k60 4:2:0 internally to two SD cards at 200Mb/s. Otherwise it's just too big to take in a bag somewhere, when I'm not doing a job, that's the only downside, besides it being a fixed lens that can't be changed. I'm actually waiting for the GH6 to come out to decide if I should buy that or the GH5S with a stabilized lens. All of my work is done on a tripod. Now to the main issue:

I have moved from (UHD) 4k60p to 4k 23.976p to make more cinematic footage and I have set the shutter to manual 1/48. Here's where the problem appears:

When AGC (automatic gain control) for the video signal is enabled (which it is by default), the lens will not go below F3.9.

In order to get down to the max of f2.8 I have to disable AGC for video but then everything is too dark unless I manually flip the switch for Low, Medium and High gain for the video signal. I do not have access to manually adjust the ISO to my knowledge as there's no options to change that in any way and the manual doesn't help there.

Can someone explain to me what is going on here? I thought that a lower F number was better or is what the camera is doing correct to compensate for something? Or is what I'm trying to do not really meant to be done since this is a broadcast camera and everything is supposed to be automatic?

To be clear the footage at F3.9 looks fine but it could be brighter, but a transform to rec 709 with gamma 2.4 seems to correct that brightness issue from the HLG setting, which is just expanding the flat Log image, right?

Thinking back, I probably should have got a GH5 or GH5S instead but I didn't want to learn about different lenses. But the camera has been great for what I do, which is recording events where the camera doesn't move - especially outside on a football field in the press box - the 20x zoom is very helpful there.

Comments

Musicvid wrote on 8/28/2020, 11:31 AM

It may be that way to protect your sensors in case of a sudden burst of light at that shutter speed. There is no real reason to go outside REC 709 gamut as far as I can see. I have no familiarity with the camera.

DougT wrote on 8/28/2020, 11:55 AM

You need to read up on exposures, F-stops, ISO, and all. AGC is trying to adjust the amount of light. F-stops, exposures are capable of doing the same thing. You don't want to use AGC and manually adjust at the same time. It is usually an either/or situation. A lower f-stop is not "better", it is just an option that allows you to shoot with either a faster exposure or lower light. Study and read and it will make more sense.

fr0sty wrote on 8/29/2020, 9:49 AM

Higher F stops tend to be sharper, since the depth of field is much greater, lower f stops, the depth of field (area that is in focus) can be as small as a few inches once you start dropping below 2.8, so for instance the eyes might be in focus, but nose and ears are soft. This is a good thing for some uses (much more cinematic, and super-fast lenses (1.4 or lower) wide open look kinda dreamy), a bad thing for others. For instance, shooting fast moving subjects at these speeds is near impossible to keep in focus. Even filming a band standing still on stage with a tripod, you're constantly adjusting focus as you move from one subject to the next.

For you, I would recommend the Panasonic S1, because in addition to being far better at low light than the GH series, it has more dynamic range, so it is better able to take advantage of HDR's 16 possible stops, at 12.2 usable stops vs. just over 10 for GH5/s. It also can be charged over USB-C, which makes that super convenient, and has other cool features like exposure leveling for timelapses, and Pro-Res RAW recording over HDMI (coming in the 2.0 fimrware).

Last changed by fr0sty on 8/29/2020, 9:52 AM, changed a total of 2 times.

Systems:

Desktop

AMD Ryzen 7 1800x 8 core 16 thread at stock speed

64GB 3000mhz DDR4

Radeon VII

Windows 10

Laptop:

ASUS Zenbook Pro Duo 32GB (9980HK CPU, RTX 2060 GPU, dual 4K touch screens, main one OLED HDR)

Teagan wrote on 8/29/2020, 10:08 AM

Higher F stops tend to be sharper, since the depth of field is much greater, lower f stops, the depth of field (area that is in focus) can be as small as a few inches once you start dropping below 2.8, so for instance the eyes might be in focus, but nose and ears are soft. This is a good thing for some uses (much more cinematic, and super-fast lenses (1.4 or lower) wide open look kinda dreamy), a bad thing for others. For instance, shooting fast moving subjects at these speeds is near impossible to keep in focus. Even filming a band standing still on stage with a tripod, you're constantly adjusting focus as you move from one subject to the next.

For you, I would recommend the Panasonic S1, because in addition to being far better at low light than the GH series, it has more dynamic range, so it is better able to take advantage of HDR's 16 possible stops, at 12.2 usable stops vs. just over 10 for GH5/s. It also can be charged over USB-C, which makes that super convenient, and has other cool features like exposure leveling for timelapses, and Pro-Res RAW recording over HDMI (coming in the 2.0 fimrware).

Thanks for the advice and answer, that makes sense. The S1 does look pretty good relating to specs, especially with that 12 bit raw out to my ninja V. I think one problem I'd have is that I'd still like to record internally (if possible with prores raw out to HDMI at the same time) but there may be a problem with storage on the SD cards because most of the codecs are h.264 while there's only one h.265 at 72Mb/s. Perhaps that's enough for good quality 4k.

Now one thing that would sell me with the S1 (or soon S5 being announced in a couple days) is Raw recording over USB-C like the black magic pocket cinema camera 4k. The only problem with that camera is the lack of auto focus while recording, which makes sense because it's for cinema.

The GH5/s don't have Raw to my knowledge but that would definitely be something I'd be interested in for future proofing with the S1/S5, along with recording in HLG for that 2020 gamut. But with Raw I'd get any gamut I want...

Also, just noticed that Davinci Resolve doesn't support prores raw. So that's going to be a problem. I don't have macs but would transcoding to prores 4444 fix this? Also just saw that VP18 may get prores raw support soon.

Also, is there a good free way to transcode prores raw to prores 4444?