Blackmagic Forum

App version 1.3.00111, shooting outdoors on a sunny day with a ND filter on iPhone 15 Pro Max, 24mm lens, 4K, 30 fps, shutter angle 180 degrees.

Per my usual practice, I set the Zebras to come on at 95%.

When recording in Rec. 709, the zebras appear at around ISO 250. The image looks well exposed on the screen and when opened in DaVinci Resolve.

When recording in Apple Log, the zebras don't show up until I exceed ISO 1250. At this ISO, the image is extremely over exposed and blown out. This happens whether I display a LUT or not. (Using the built-in Rec. 709 LUT or the OneLut.) But if I dial back to ISO 250, the recorded and displayed image look fine.

I've uninstalled and reinstalled the app, and still have the issue.

Is there something I'm overlooking or is this an issue with the current version of the app?I don't recall this being an issue in the past, but during the winter months I shoot infrequently.

Are you setting zebras to 95% for both Rec. 709 and Apple log?

AlNash wrote:When recording in Apple Log, the zebras don't show up until I exceed ISO 1250. At this ISO, the image is extremely over exposed and blown out.

You've omitted a vital piece of information: if you shoot at 1250 and protect for the zebras, do post-production adjustments restore the data which appears to be blown out on the screen of the phone or when you first bring the clip into Resolve? Or is the data actually clipped?

If in doubt, upload a sample frame to a file sharing site and post a link here.

Hi Al,

I don’t get a clear understanding of your process for determining exposure from your post. I wonder whether this is a process problem rather than a problem with the Blackmagic Camera app. Since you raise that possibility yourself, maybe have a look at the resources below.

This video is about Canon cameras, but that’s beside the point for the purpose of this discussion. You can ignore what he says about base ISO. Note, in particular, that his zebra values are not the same for Rec. 709 and Log, and that he chooses a middle grey card as a target:
How to Expose Canon Log on the EOS R5 and R6


Also, have a look at this cinematography.com thread, the posts by David Mullen and Phil Rhodes in particular:
Setting proper exposure when shooting Slog?
https://cinematography.com/index.php?/f ... ting-slog/

This Alister Chapman article may also be useful:
How To Correctly Expose S-Log3 – a7S III / FX3 / FX6 / FX9
https://sonycine.com/articles/how-corre ... fx6---fx9/

In this case, since he's judging exposure with zebras, that's really all that's at issue. If zebras are working as advertised, there will be no clipped data (if there were no zebras). It's true that the ideal ISO/exposure for iphone15+BM app seems to be in some dispute. But that's another issue.

Unprocessed log will of course look blown out and washed out. But it's also likely in this case that the normalizing LUT(s) -- Applelog to rec. 709 -- is mapping the values "high" based on his particular exposure. So while the shot may *look* blown out even with a rec 709 LUT, reducing the levels in a node which precedes the LUT should restore the data (if in fact he didn't clip anything).

Why a LUT?
RCM knows about Apple Log plus Rec. 2020 and is doing a better job.

Sure, but the OP mentioned that he applied a LUT and the shot was still blown out, so for reference.... It would seem this app has attracted a number of shooters unfamiliar with log and what it requires in post.