Lumens And EV Exposure

Started Nov 21, 2017 | Discussions thread
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BlackNinja101 New Member • Posts: 20
Lumens And EV Exposure

Hey guys, I need some help trying to figure out exposure. 

So basically, I did some research on Shutter Speed, Aperture, and ISO in relation to stops and exposure when utilizing the EV bar on the camera. I know that doubling your shutter speed decreases the amount of light by half, and slowing it down by half increases or doubles the amount of light. The same goes with ISO.

I did some tests with a lightbulb I have, which is rated at 5200 lumens, and a DIY diffusion panel, which if I remember correctly decreases light by 1.5 stops. I cant remember the exact amount for sure. But I'm using Savage Plastic from B&H. Got it a while back and I think it's the Medium Duty version.

Anyway, here is my question or dilemma. I plan on shooting videos soon, and I want a relatively deep depth of field, something like f/6 - f/10, with a low as possible ISO of hopefully 100.

I did some tests with a basic setup using my Sony a6500 and Sigma f1.4 30mm lens. I had some stuff propped up on the floor and in the first shot its purely direct light using a 24x24 softbox. After that in the second picture, I have the diffusion panel being used to diffuse the light (much better shadows and fill). As you can see in the photo's data, I have the aperture stopped down to f/10 for the deepest DOF I'd probably want in my videos. The third photo is the desired minimum shutter speed for when I'm recording, and I have the ISO boosted to compensate.

Now, here's what I'm asking. Given that each stop is the equivalent of doubling or halfing the light. The difference from the 100 ISO to 8000 ISO is about 6+ stops. Meaning I'd have to double the amount of light 6 times, if what I read prior to this post is correct.

100 > 200 (1) > 400 (2) > 800 (3) > 1600 (4) > 3200 (5) > 6400 (6) > 8000 (6+)

So with my lightbulb being rated at 5,200 lumens, using that math would mean I'd need a lightbulb rated at 332800 lumens!? Just to bring the ISO back down to 100 if I keep my shutter speed at 1/100, and my aperture at f/10 with the diffusion panel? I know that number is crazy high, and it seems like my math is way off. But I did some testing with two lightbulbs in my bathroom on a lit test scene. One lightbulb was rated at 840 lumens, the other at 1700. And sure enough, the 840 lumen light bulb was showing -1 stop in exposure. So that leads me to think my math is right. (I even added a second bulb which had the same lumens of 5200 to the test scene and I could increase my shutter speed by one stop as well too, which is still too slow)

But I wanted to double check and ask about this first. Does that even seem logical (the high lumens I mean)? I'm trying to keep my ISO down as much as possible to eliminate noise in the video, and keep in mind this is just assuming its one light source. I'm sure I'll have at least 2 - 3 with some spot lights here and there as well, and I can always boost my ISO (preferably no more than 500) and even open the aperture a bit too, so I can compensate for light and all that.

So I guess my question is, how would I go about calculating "accurately" how much light or lumens I'd need to properly expose that test scene. Because 332800 lumens seems crazy.


 BlackNinja101's gear list:BlackNinja101's gear list
Sony a6000 Sony a6500 Sony E 16-50mm F3.5-5.6 PZ OSS Sigma 19mm F2.8 DN | A Sigma 60mm F2.8 DN Art +3 more
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