# Basic light meter questions



## kat.hayes (Mar 28, 2018)

I'm using a 5DM3 and a Sekonic L-478D

1.) I dial in T=250, F=2.8 and the meter tells me to use an ISO of 20. The lowest ISO on the 5DM3 is 100 as far as I understand it, what do you do in this situation? Does this mean I have too much light and need to close down my aperture?

2.) I want to shoot some video so I switch to HD mode. I want to control F stop, Shutter, and f/s and let it provide me with ISO, though the way it is set up I enter the shutter, ISO, and f/s and it provides the aperture. I do not see any other options for this. How do I enter my desired aperture as a controlled value?

Thanks in advance.


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## hne (Mar 28, 2018)

kat.hayes said:


> 1.) I dial in T=250, F=2.8 and the meter tells me to use an ISO of 20. The lowest ISO on the 5DM3 is 100 as far as I understand it, what do you do in this situation? Does this mean I have too much light and need to close down my aperture?



Yes. Stop down lens aperture, go faster on the shutter, turn down the light or go indoors. That light level sounds like outdoors on an overcast day.


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## Sporgon (Mar 28, 2018)

I presume in question one you’re using the 478 as a flash meter ? If you must shoot at f/2.8 just reduce the flash power to 1/4 or even 1/8 output.


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## LDS (Mar 28, 2018)

kat.hayes said:


> 1.) I dial in T=250, F=2.8 and the meter tells me to use an ISO of 20. The lowest ISO on the 5DM3 is 100 as far as I understand it, what do you do in this situation? Does this mean I have too much light and need to close down my aperture?



Yes, it's too bright for your settings. You have to change aperture/shutter speed - or use a neutral density filter if you need those settings.



kat.hayes said:


> 2.) I want to shoot some video so I switch to HD mode. I want to control F stop, Shutter, and f/s and let it provide me with ISO, though the way it is set up I enter the shutter, ISO, and f/s and it provides the aperture. I do not see any other options for this. How do I enter my desired aperture as a controlled value?



Shooting video, you have far, far less control on shutter speed, and it is also correlated to the fps (see for example http://www.red.com/learn/red-101/shutter-angle-tutorial). 

AFAIK, in movies, it's not common to change ISO as you would do for still, because it will make more difficult to have a common "visual look" within a sequence and related ones, so you'll mostly work on aperture - and/or lighting and filters. 

Cameras used for news and the like may employ auto ISO functions, but you don't usually use a separate meter in such situations.


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## kat.hayes (Mar 29, 2018)

I was shooting outdoors with natural light, no flash. I guess I just didn't understand why it was telling me ISO 20, since the 5DM3 doesn't go that low with ISO, though some cameras could possibly...

As far as the video question, isn’t being able to control aperture for depth of field with video just as important as it is with photography? That is the one variable that I need to control more than anything with video...

Thanks.


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## ajfotofilmagem (Mar 29, 2018)

Use an ND filter will help you to set an "ordinary" ISO such as 100 or 200.


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## cayenne (Mar 29, 2018)

I'll need to dig my light meter out to find out the settings I've used, been awhile and I forgot what it sets up as...

BUT one tidbit...when shooting video, you generally want your shutter speed to be close to 1/2x fps

So, if you are shooting at 24fps, you want your shutter speed to be 1/50,.....if you shoot at 30fps, you have your shutter speed at 1/60.

That is really not variable...so, all you have left to play with, is aperture and ISO.

Like others have said, if it is extremely bright outside, you might need to use a NDF. I shoot mostly indoor stuff (cooking videos, etc) and can more readily control my lighting since it is indoors.

I'll go look at my meter if I can find it....I didn't set mine up with "T" values....I just used regular f-stop, ISO, shutter speeds for mine.....all my lenses are regular L series canon EF lenses...I don't have any cine ones with T values.....

Anyway...that's some info I'll try to find my meter to look at to see if I can help with your other questions.


HTH,

cayenne


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## kat.hayes (Mar 29, 2018)

I had my shutter at 1/50.

The only T value I used was for shutter, I didn't really understand why it was a T value, and I am also using regular L lenses. I just figured that in the world of light meters that was how shutter speed was represented for some reason. I am using the default settings on the meter, at least I think I am, I guess i could have possibly changed some setting without realizing it. If this meter doesn't allow for setting aperture in movie mode, I guess I just need to find on that does...

Thanks.


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## LDS (Mar 30, 2018)

kat.hayes said:


> I guess I just didn't understand why it was telling me ISO 20, since the 5DM3 doesn't go that low with ISO, though some cameras could possibly...



Some digital backs, and of course some films, go below ISO 50. For years, I used Kodachrome 25 (ISO).

In bright daylight 1/250 is too long for f/2.8. IIRC the old thumb rule for film and ISO 100 was 1/125 at f/16, which means f/11 at 1/250... you'll need to go well below ISO 100 for your f/2.8 setting.



kat.hayes said:


> As far as the video question, isn’t being able to control aperture for depth of field with video just as important as it is with photography? That is the one variable that I need to control more than anything with video...



Yes, but you have far less control on shutter speed (also called shutter angle in video), did you look at my links? In a video frame, you need the "right" amount of blur so when frames are shown consecutively, the movements looks "natural". If the shutter speed is higher or lower, motion won't look natural.

So, most of the time shutter speed is fixed once you selected a given fps. That lets you only able to change aperture or ISO.

Once again, changing ISO can have side effects on the image look, depending on the camera. Noise, colors, dynamic range can all be affected. You may not want this inside a given sequence, or among similar sequence - it makes post-processing longer and more complex, and expensive - of course it is fully acceptable when changing, for example between day/night sequences, or outdoor/indoor ones.

Thereby, most of the time you control exposure with the aperture. Yes, it does impact DOF, that's why in movies ND filters are much more used than in stills - some cameras have even built-in ND filters.

I understand their use is far easier in highly planned shootings like in movies - but that's where external meters are most often used - when there's no time to plan and use filters you may want to use a given aperture and change ISO, but evidently the designers of your meter didn't take this situation into account. The math is not hard, or you can change ISO until you get the desired aperture.


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## Talys (Apr 13, 2018)

LDS said:


> In bright daylight 1/250 is too long for f/2.8. IIRC the old thumb rule for film and ISO 100 was 1/125 at f/16, which means f/11 at 1/250... you'll need to go well below ISO 100 for your f/2.8 setting.



Yeah, 1/250 f/2.8 is way slow for ISO100.

Going by the old Sunny 16 rule, daylight exposure for f/2.8 lenses on ISO 100 wide open was 1/3200, if I recall  Of course, nobody had that back then...

Since you're recording video outside, why not just use live view and histogram to figure out exposure, instead of the Sekonic? I mean, it doesn't help if the metered exposure is X, but the video looks crappy.


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## LDS (Apr 13, 2018)

cayenne said:


> I'll go look at my meter if I can find it....I didn't set mine up with "T" values....I just used regular f-stop, ISO, shutter speeds for mine.....



Sekonic meters usually use the "T" symbol (from "exposure Time") instead of "shutter speed". It doesn't mean the "T" aperture values on cine lens. 

Those with cine features may let also to set it in f/s and shutter angle.


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