Determing a useful ISO. Brevis and EX1.

[Phil Gerke]

Hey folks,

 

I may be gaffing an indie feature in April and as of now the plan is to use the new EX1 with a Brevis 35 adapter and a Nikon SLR prime set. I am curious as to what would be the best way to set up my meter in terms of a usable ISO rating.

 

I understand that rating video like film is not a great idea in the sense that a video cameras effective ISO fluctuates at various light levels. Forgive me if that is incorrect I am still learning a lot about this area. Film is much easier in this regard. How useful is it to grab the camera setup, hook up to a scope, and shoot a grey card etc... I am not even clear on the process, but would that gain much?

 

What it boils down to is that I would like to be able to be lighting while camera dept. is getting all squared away and I don't want to have to wait for a monitor to be up before I really do some work. Granted once a good monitor is up I'll tweak from there, but I want to at least be able to come close.

 

Also, is it just as simple as combing the F stops of both lenses to get your actual stop? Seems like the math should be harder. The 35 adapter setup is still pretty new to me and certainly raises questions.

 

We should have plenty of opportunities for testing and such and I know thats what is really important, but testing is a waste of time if you don't know what questions to ask.

 

Thanks for any help, I hope this makes sense.

 

Phil Gerke

[Jonathan Bowerbank]

It's sort of a question that's so specific you should probably only be asking the DP when it comes time to shoot. He should have an idea of what ASA he's working with for interiors, which will in turn give you an idea of what light levels you will be working with.

 

Most DP's light by eye, first and foremost. And when shooting video, I've seen many who usually adjust the exposure at the last second. So as long as you work together and get the contrast ratios the way you want, you shouldn't have to worry too much specific ASA.

[Michael Maier]

It's sort of a question that's so specific you should probably only be asking the DP when it comes time to shoot. He should have an idea of what ASA he's working with for interiors, which will in turn give you an idea of what light levels you will be working with.

 

Most DP's light by eye, first and foremost. And when shooting video, I've seen many who usually adjust the exposure at the last second. So as long as you work together and get the contrast ratios the way you want, you shouldn't have to worry too much specific ASA.

 

Yeah, but I find it very useful and important to work with the same T-stop through a scene rather than setting the exposure for the shot, specially with a 35mm adapter where you will be changing lenses.

[Walter Graff]

The most accurate way to measure Exposure Index for a video camera at a PARTICULAR STOP is with a chip chart, waveform, lights and meter. Light the chip chart evenly. Adjust the cameras iris until the the crossover point on the waveform is 55 units. See where the F-stop is. If that is not the f-stop you want to work from, adjust your lighting levels until you get the crossover on the money at the stop you want. Now read the chart with your meter adjusting it until your meter matches the lens. You now have the most accurate measurement of the cameras exposure index AT THAT F-STOP. It will be well in the ballpark, but frankly nothing beats a good monitor in video, especially when it comes to highlights.

[Satsuki Murashige]

Yeah, but I find it very useful and important to work with the same T-stop through a scene rather than setting the exposure for the shot, specially with a 35mm adapter where you will be changing lenses.

The original poster said they were shooting with the Brevis and a set of Nikon still lenses which are marked in f-stops and are all over the place in terms of aperture and actual light loss thru the lens. The slowest lenses in the set will probably be in the f/2.8 - f/3.5 range. I've also noticed when shooting with the Brevis that stopping down the SLR's aperture from wide open down to about f/2.8 doesn't seem to affect the exposure at all - I have no idea why. Beyond f/4, the exposure begins to drop in a normal way.

 

So I think it may be more helpful to compare apples to apples, so to speak. I'm familiar with the HVX+Brevis+Nikkor setup which I'd estimate is in the 160ASA - 200ASA range depending on the gamma, at 24PN and 1/48 shutter. The EX1, due to its 1/2" sensor, is definitely faster than the HVX. I haven't compared the two cameras side-by-side, so I don't know how much faster. Hopefully this is a good starting point for you to do some tests.