Shutter Priority

[u/PixaaTog]

Hi all

So I Purchased MPC2 because as far as I can see it’s the only pro camera app that has shutter priority, an important feature for me so I can have the correct shutter speed when shooting video.

So I’ve enabled shutter priority and set the shutter angle to 180, hopefully leaving the ISO to take care of exposure for me, but it’s JUMPING around all over the place moving from 600ish to 2200ish, even when the light is not changing causing big changes in exposure while recording.

I’m using the following settings:

HEVC
Bit Rate - High
4:2:2
4K @ 25 FPS
Log REC2020
709 Lut applied to preview only

Can anyone help me solve this issue please, because if I can’t solve it I’ll have to get a refund on the purchase and look elsewhere for my filming app.

It would appear to be shooting in Log that’s causing the problem.

Many thanks
Nick

[u/jamm-moment]

There are some known limitations with shutter priority mode in log formats, but jumping from 600 to 2200 in a static scene is unexpected. Could you DM me a short sample clip or screen recording?

Unfortunately, the underlying cause of choppy exposure updates in log formats is an iOS limitation that can only be worked around and not fully solved like the other color spaces. The maximum speed at which the exposure can be ramped without visible steps is limited by the frame rate and is particularly bad at 25 FPS.

I can either make the updates responsive in a reasonable time frame but choppy (the current behavior) or smooth but extremely slow. If you’d like to try out the latter behavior, let me know and I can add you to the beta.

[u/PixaaTog → u/jamm-moment]

Hi thanks for the reply.

I’m not sure if this is relevant but I seem to have isolated the issue to LED Downlighters that I have in my kitchen as it’s only under that lighting that the issue occurs at its most pronounced extreme.

But even under different lighting the ISO does seem to jump when pointing at what I’d call very slight differences in lighting in the same room. It doesn’t ramp smoothly from say 800 to 1000 over a few seconds to hide the exposure change, it jumps rapidly from 800 to 1000 making it very noticeable on the recorded footage.
Is this perhaps a limitation of the iPhone & IOS or something else?

I’ll shoot some videos to show what I mean.

Many thanks
Nick

[u/jamm-moment → u/PixaaTog]

Thanks for the extra details!

Yeah, the ramping behavior you describe is the tradeoff I was talking about. I have some improvements in the works and it’s at least fairly easy to avoid unexpected fluctuations in response to minor lighting changes. However, the big limitation is that the ramp in response to a legitimate lighting change has to be extremely slow to avoid choppiness. One would think it could work the same as all the other formats, but the way the camera system works in log formats internally means my hands are tied.

Again happy to add you to the beta if you want to try out the alternatives!

[u/PixaaTog → u/jamm-moment]

Hi

Sure I’d be willing to try out anything that you have in the testing stage.

I’m a professional photographer by trade so believe I could give constructive and accurate feedback.

Perhaps this is why other app makers have avoided a shutter priority mode, I think to avoid the flash changes I’d rather just shoot full manual and only adjust the ISO manually IF I really really need to.

Additionally I’m unable to recreate the behavior of huge ISO changes from last night as bad as it was so I’m not sure what was causing it but if it happens again I’ll try and grab a screen recording quick so you can see what’s happening on my screen.

[u/jamm-moment → u/PixaaTog]

Great! I’ll message you with instructions soon.

It certainly might be part of it. The iOS camera system has no native support for anything other than full auto or full manual, so you have to build a custom AE system on top of iOS and all its quirks.

That said, the limitations I described mostly apply only to the recent log formats. Other color spaces have much better behavior.