A7SmII Shutter and Framerate question

[Ryan Patrick O'Hara]

So I own an A7S, but almost never do video with it. It's my personal photography camera, but I've bought some cages and accessories so that I may rent it out. Recently while exploring the camera I noticed that when I went to 60p, the shutter I had before in 24p didn't change, which was 1/50.

This is impossible, right? How can you have an exposure of 1/50, when a wide open shutter at 60p should be 1/60.


I didn't solve the question and it's been raised again by another cinematographer. Just curious if there is a glitch in the camera, and it's really 1/60, or if there is something I am unaware of.


-Ryan

 

[Viscount Omega]

I don't understand why it's impossible. The shutter speed is controlled electronically instead of mechanically.

What I mean is, I thought these digital cameras always simulated a mechanical camera's rate and amount of light hitting the frame. The shutter was never like a mechanical camera.

 

[thekreative]

it is impossible because 60 frames at 1/50 of a second is more than one second.:smile:

 

[Viscount Omega]

it is impossible because 60 frames at 1/50 of a second is more than one second.

Right, but I thought these shutter speeds/fractions of a second were never meant to be taken seriously in these digital cameras. Same thing with them using the term "ISO" from the film world.

There's no spinning disk in front of the frame, it's just a simulation of that amount/rate of light.

 

[deltoidjohn]

Most likely you'll end up with duplicated frames - probably a 30p video in a 60p stream.

Most video cameras can shoot slower shutterspeeds than their frame rate. I think it was really only during only the DSLR revolution that cameras lost this function, because stills camera engineers didn't understand the concept. Plus a whole new generation of "film-makers" came along who thought anything other than a 180 degree shutter was not possibly a creative option. But videographers for decades have used this trick to shoot in lower light. Even film-makers have done this too - legendary WWII cameraman Damien Parer routinely shot at slower frame rates, by physically slowing the motor with his thumb, in order to shoot with longer exposures. The trick is knowing which shots you can do it on without it being obvious.

 

[Viscount Omega]

...possibly a creative option.

I'm thinking of using it for in-camera motion-blur effects. City lights, cars, night, walking on sidewalk, wide-angle lens w/ stabilizer, 24p, 1/15th shutter looks like the POV of someone hallucinating or drunk.

But videographers for decades have used this trick to shoot in lower light.

I've already used it on my current project in a graveyard and on establishing shots in a neighborhood at night. Both were just static shots on a tripod. 24p, 1/20th and 1/15th of a second. Helps keep the ISO down for a cleaner image. I never knew there was a rule against it. :laugh:

 

[Ryan Patrick O'Hara]

Most likely you'll end up with duplicated frames - probably a 30p video in a 60p stream.

Most video cameras can shoot slower shutterspeeds than their frame rate. I think it was really only during only the DSLR revolution that cameras lost this function, because stills camera engineers didn't understand the concept. Plus a whole new generation of "film-makers" came along who thought anything other than a 180 degree shutter was not possibly a creative option. But videographers for decades have used this trick to shoot in lower light. Even film-makers have done this too - legendary WWII cameraman Damien Parer routinely shot at slower frame rates, by physically slowing the motor with his thumb, in order to shoot with longer exposures. The trick is knowing which shots you can do it on without it being obvious.

That is interesting. I don't know what cameras you shoot though, because none I work with can do that. I think the C300 might have some sort of long shutter mode. Otherwise, this is new to me. Arri and Red cameras don't do this. :/

 

[Bern Caughey]

Ryan,

Perhaps Sony has some wizardry in the machine, but otherwise I'd think setting the shutter to a speed longer then the reciprocal of the framerate is impossible, & probably a glitch. Panasonic GH cameras had (have?) the ability to set too long a shutter but doing so forced the camera into a low bitrate mode, & I think duplicated or dropped frames, so definitely a glitch.

Is there an appropriate exposure shift when going from 1/50th to 1/60th when filming 60p on the A7sII?

 

[Viscount Omega]

Is there an appropriate exposure shift when going from 1/50th to 1/60th when filming 60p on the A7sII?

Yes.

I think duplicated or dropped frames, so definitely a glitch.

If you're intentionally shooting motion blur or it's a static shot in very low light, duplicated or dropped frames don't matter. So, not a glitch, a feature!

 

[Bern Caughey]

If you're intentionally shooting motion blur or it's a static shot in very low light, duplicated or dropped frames don't matter. So, not a glitch, a feature!

Not on the GH cameras as the low bitrate made the images unusable.

 

[Viscount Omega]

Hmmm. I don't think the a7sII lowers the bitrate. If you say the GH cameras made the images unusable, I probably would've noticed with my Sony footage but it looks fine. In low light, I have no problem shooting at 24p and 1/20th of a second as long as there's not a lot of motion in the shot:

 

[deltoidjohn]

That is interesting. I don't know what cameras you shoot though, because none I work with can do that. I think the C300 might have some sort of long shutter mode. Otherwise, this is new to me. Arri and Red cameras don't do this. :/

Yes, but the Arri and Red cameras are not conventional "video cameras", they are "cinema" cameras which lack many of the automatic features of other cameras, like AF or Program modes. Instead, they assume the user knows exactly what they are doing at all times. As such, to get a longer shutter speed these cameras first require you to lower the frame rate manually (down to as low as 1 fps) before setting a slower shutterspeed. Same outcome, it just requires more user intervention to get there.

C300 I'm not sure about, but previous Canon cameras have all had this ability (XF100, XF200, XH-A1, etc). It really is a pretty standard feature, though the C300 might be from the Cinema division where things are done a little differently to the broadcast division.