63db S/N Accurate on F3?

[Ola Christoffersson]

Wouldn't this depend on wether you are using an interlaced or progressive mode? 1080i gives you one stop over 1080p. I think I recall reading that the F3 is ISO800 at 0 dB in interlaced mode. Hence ISO6400 @ +18dB would be correct. Right?

[Andy Shipsides]

So I did some tests in the standard REC709 gamma mode. And here is how it rates. Amazingly clean through the range. This is the test I showed Mitch.

-3 db - 640 ISO
0 db - 800 ISO
3 db - 1250 ISO
6 db - 1600 ISO
9 db - 2000 ISO
12 db - 3200 ISO
18 db - 6400 ISO

Tests where completed with DSCLabs chart, Sekonic Meter, and Leader scopes. I preformed the test under both tungsten, and daylight balanced lights for accuracy. Camera was at 1080 23.98, 180 degree shutter, Gamma = REC 709, Auto Knee OFF, Black Gamma = 0, Black Level = 0 (edit).

Using the Cine gamma modes (Cine 1,2,3) lowers the gray point effectively lowering the ISO value, but for comparing to any DSLR these numbers are accurate.

I'm going to post my findings on our blog in a couple days with pictures.

Andy

[Daniel Doherty]

Ola's right. It would be more helpful if the tests would include the video format. Personally, I will be using 1080 24p for most of my shooting.

[Andy Shipsides]

Good point. I'll add that above.

[Daniel Doherty]

Thanks Andy.

[Andy Shipsides]

A couple stills from my test.

I grabbed this out of Clip Browser (note the settings):

http://blog.abelcine.com/wp-content/...02/F3_6400.jpg

Frame grab (off EX recording):

http://blog.abelcine.com/wp-content/.../F3_6400_2.jpg

[Timur Civan]

Jeez. astounding.


I was testing in cinegamma.

Lemme reup, and match your settings.

(edit)

The only way i got the camera to Read 6400 ISO was in 59.94 Interlace mode. Gotta bust out the light meter.

[Andy Shipsides]

I didn't test the camera in ISO mode vs dB gain mode. So it could possible be limited in someway. But I don't see why shooting at a higher frame rate (59.94i) would effect ISO options. I'll give a more detailed report tomorrow.

Funny enough Sony's manual even suggest that 18 db is the same as 6400 ISO. Excerpt from F3 manual:

[Timur Civan]

well it seems like your readings are based on actual exposure, not what the camera "says". I trust a light meter. If 18bB is 6400 ISO, and it looks like that! its astounding.

[Daniel Doherty]

Andy,

Shooting at a higher frame rate may not affect ISO settings but shutter speed/angle definitely will. Also, as Ola stated previously, interlaced appears to be more sensitive than progressive.

Thanks,
Daniel

[Andy Shipsides]

Thanks Daniel

Shutter speed is a limitation in exposure length, so it would not effect ISO. As I decrease my shutter angle I am reducing exposure length and my image gets darker, this is not a change in sensitivity just exposure. Increasing my frame rate has the same effect, regardless of if the camera is capturing an interlaced or progressive image it will always have a reduced length of exposure.

In 59.94 mode it is possible they are trying to compensate for the shorter exposure time by adding additional gain, but that does not seem to make sense. I'll do some more testing, and if anything it should only be dependent on gamma mode.

Another note.. The F3 appear to always capture images progressively, if you turn on dual link output when in 59.94i you will get a 59.94 progressive out of the dual link connector. So the interlaced recording is just pulling odd and even fields from the progressive stream.