Skip to the end of navigation

Welcome to the Community!

FS7

Showing results for 
Search instead for 
Do you mean 
Reply
Highlighted
Specialist
Posts: 26
Registered: ‎01-13-2016
Message 1 of 5 (1,538 Views)
Accepted Solution

Minimum illumination for kit lens

Hi,

After being somewhat disappointed over the performance of the FS7 with practical lights I had a quick look at the specification for minimum illumination. It says: 

 

0.7 lx  (lux?) but there are conditons!  +18db, 23.98P, Shutter Off, ND Clear, F1.4

 

I didn't want to amplify, as it will amplify the noise as well, But shutter off ? Mainly the lens at F1.4. (what lens is that?)

 

What I need to know is what is the minimum illumination if you are simply using the kit lens (F 4) ?

 

People have been reporting good things with a SpeedBooster but mainly in the context of usung a Canon lens. Can they be used to help the kit lens?

 

Lastly, if you were going to film in an evironment where you don't want/aren't able to take much light with you - how would you configure your camera?

Expert
Posts: 92
Registered: ‎01-11-2016
Message 2 of 5 (1,509 Views)

Re: Minimum illumination for kit lens

[ Edited ]

I mean no camera (current low light kings A7SII and Varicam LT included) does well when you shoot in the "mud" IE the very bottom of the exposure curve. 

 

Those figures that you're reading are marketing figures that have no real bearing in the real world, it gets you an image, alebit a completely useless image. The same formula was used on HVX200s to claim it just needed 3 lux to get an image...yes at 3 lux you will see something....but it would be super noisy and terrible for use, but you know its there so that counts as minimum illumnation. They also claim the DVX200 needs .2lux

 

However as far as minimum illumination with the FS7 lens...its a fairly slow lens (f/4) and I like to rate the camera at 1000ISO.

 

Some back of the napkin math with a basic formula from the film days: You need 100fc at 100iso at 2.8 to have a well exposed image at 24fps 180d shutter.

 

So at f/4 at 100iso you'd need 200fc (each increase in f/stop doubles the amount of light needed)

 

At 1000ISO (each doubling of the iso halves the amount of light needed...) you'd need 1/8th the amount of light than ISO 100 at ISO 800 so 25fc. Add a third stop to get you back up to 1000ISO so lets call it 18.75 fc for a "properly exposed" image.

 

18.75 FC is roughly 200 Lux. That will get you a clean well exposed image on the FS7. Lets say you are ok with a little noise and hoot at the native 2000 ISO thats 100 lux you need for a well exposed image with an F/4 lens. Use a F/2.8 lens and that figure can drop down to 50...use an f/1.4 lens and that figure drops to 12.5Lux.

 

So how did they get that ridicoulous lux rating? Take 12.5 lux and add some gain (each 6db of gain equals a stop of exposure...so +18dB is 3 stops of extra gain) and you're down to 1.56 lux. Increase the shutter to 360d (so from 1/48th expsoure time to 1/24th) which adds another stop of exposure and you're down to .78 Lux....which taking into account our fuzzish math is pretty close to their advertised minimum illumination rating and completely useless.

 

 

How much light is that?

Well an Arri 300W Tungsten Fresnel generates 45 lux at 32ft away. 

A Litepanel Chroma (a small on board LED light) generates about 60 Lux at 9ft away at full power.

 

If I had no control over my environment I guess I'd be in a documentary style shoot or live event shoot:

I'd probably make sure to test out different custom profiles and shoot one one of those settings and avoid log so I don't have to spend time color correcting in post, use a metabones speedbooster with a fast zoom or prime to get me as fast an f/stop as possible, and bring some kind of LED battery powered solution with me. An on camera LED, a 1x1 LED, anything to just get my subject out of the mud and into proper exposure. Even a cheap on board LED can provide enough exposure

 

This camera does not need much light to generate a good image...but it does need some light.

Stray Angel Films
www.strayangelfilms.com
Specialist
Posts: 26
Registered: ‎01-13-2016
Message 3 of 5 (1,497 Views)

Re: Minimum illumination for kit lens

 

thanks very much, a great explanation

Expert
Posts: 134
Registered: ‎02-04-2015
Message 4 of 5 (1,479 Views)

Re: Minimum illumination for kit lens


dcolmenares wrote:

At 1000ISO (each doubling of the iso halves the amount of light needed...) you'd need 1/8th the amount of light than ISO 100 at ISO 800 so 25fc. Add a third stop to get you back up to 1000ISO so lets call it 33.5 fc for a "properly exposed" image.


This is wrong. If you need 25fc for proper exposure at 800 ISO, then you need less at 1000 ISO, not more. 

Expert
Posts: 92
Registered: ‎01-11-2016
Message 5 of 5 (1,446 Views)

Re: Minimum illumination for kit lens

And this is why I didn't become an engineer!

 

Thank you for catching it, fixed the comment.

Stray Angel Films
www.strayangelfilms.com

Get Social

Share your ideas Watch YouTube Support Videos follow us on Twitter Visit us on Facebook