Using Slog to shoot day exteriors, plus stars at night

[Thomas Kaufman]

Hi, everyone,

I plan to use slog to shoot daytime exteriors next week, as well as a night time shot of stars (out in the country, away from city lights).

I've never used the slog function before, and would be grateful for any information regarding exposure.

There are threads posted here from last year, but I am unsure how up-to-date those comments are.

Many thanks,

Tom

[Nate Weaver]

Originally Posted by Thomas Kaufman

I plan to use slog to shoot daytime exteriors next week,
I've never used the slog function before, and would be grateful for any information regarding exposure.

When you have a situation where your dynamic range isn't so wide, like an interior that's been lit (including fill light), the camera in S-Log has latitude to spare and you should take care not to overexpose. It's easy to do. In those situations, your exposure histogram will have some blank space on the right if you're exposing correctly. Put another way, if dynamic range is low, underexpose by a stop.

Daylight exteriors, if it's hard sun, and you're not filling in the shadows with lights or reflectors, you can actually hold sun side and shadow side if you split expose. And it will come out looking nice. You won't get the luxury of exposing it "correctly", in which you underexpose a bit and let the LUT in post bring things back to level.

If you do this, you'll likely be adding only a little contrast back in post as opposed to the former situation where you add a lot of contrast back via the LUT.

In the grabs below, I actually have Resolve adding contrast back via the LUT Resolve provides for Alexa Log-C, but I further tweak it so I can still keep my highlights from clipping. Applying the S-Log or Alexa LUT and doing no further work would have the whites clipping on the hat on the left.

[Alister Chapman]

The easiest way to expose S-log correctly is to invest in a decent 18% grey card and use the cameras built in spot meter to expose the grey card at 38%. A white card should then meter at about 68%. This will place your mid tones in the correct part of the log curve for the best results. Over expose and you can end up with a lot of extra compression on skin tones and the mid range, under expose and the image can be come excessively noisy after correction in post.

Why Nailing Your Mid Range Will Make Post Production Happy. Even with Cingammas and Log. |

S-Log and contrast ratios. Why is Grey 38 and white 68? |

[Mark Kenfield]

Alister,

For low key exposures, where you want your subject's face to be considerably underexposed - how do you suggest setting the exposure to get the cleanest image possible (given the compression of the SLOG curve)?

Cheers,

Mark

[Alister Chapman]

Log compression increases the brighter you expose, so in an underexposed shot log compression will not be an issue. If you under expose then noise will become an issue, as by definition if you have underexposed you will be pulling your material (and noise) up more than if it is correctly exposed in post and this will lead to more noise.
If your talking however of a low key scene, that is a dark scene as opposed to an underexposed scene then the same rules apply as for any other scene. It is how you light (or don't light) the scene that will dictate the mood and feel of the scene. Your log exposure should then still be used to capture the optimum amount of information so that final brightness decisions can be made in post. If you scene is adjusted in post to make it darker, then noise will as a bonus decrease.

For a very dark scene you may not be able to use a grey card and exposure is harder to judge, but you definitely don't want to underexpose you still want skin tones around 40%-50%.

[Thomas Kaufman]

Great information, everyone! Thanks so much.

Has anyone had experience filming a star field at night using the Gemini and S-Log? I have a Superspeed lens set so can shoot at t/1.3 but not sure about exposure in this situation.

Also, is it possible to undercrank if shooting to an out-board recorder?

[Nate Weaver]

Originally Posted by Thomas Kaufman

Great information, everyone! Thanks so much.

Has anyone had experience filming a star field at night using the Gemini and S-Log? I have a Superspeed lens set so can shoot at t/1.3 but not sure about exposure in this situation.

Also, is it possible to undercrank if shooting to an out-board recorder?

You'll be wide open, but 6 or 12 of gain at wide open is enough to put the sky glow at 20-30IRE with a set of super speeds (and 1/24th shutter too)

You can do long frames to an outboard recorder, but the recorder will be recording many duplicate frames. Not a big deal if you take notes. I haven't done it in a while, you don't use S&Q, you use "Frame Accumulation" or something similar in the Camera Menu.

[Alister Chapman]

I use a similar technique when shooting the Northern lights. If you have very clear sky the F3 will pick out the brighter stars without needing a slow shutter etc. But if you want to capture a lot of stars consider using S&Q motion at 1fps with the shutter at 360 degrees. Any external recordings can the be sped up by the frame rate (24x for 24p) if needed. Alternately you can use the EX Slow Shutter.

However in either case the images will be noisy. I would only go down this route if your trying to capture motion of some sort. Otherwise a DSLR is a much better tool for shooting stars.

[Thomas Kaufman]

Alister,

If you use S&Q motion to reduce the F3 frame rate to 1 fps, would there be a corresponding increase in exposure time, as it was with the Varicam? Or would exposure remain the same?

If the frames would receive an increase in exposure time, would the Gemini recorder receive the same frames?

Does using S-log have any impact on the above?

thanks,