Doug Jensen
Carbonite Member
At some point during the session, jump out of your chair and yell "Get the hell out of my way and let me do this!" as you shove the colorist aside. Works like a charm.
F5: Beware, the camera's not really 2000 ISO...
- Thread starter Grug
- Start date
starcentral
Veteran
Today because I was bored I repeated my test on the F55 using 18% grey card, Sekonic LM-508 Zoom Master, 180 degree shutter, 24fps, 0db gain and found there a full stop difference between my meter (LM-508) read and the camera's own ISO rating. (as I did 2.5 years ago)
I tried lumisphere up or down without any difference in reading.
Conclusion: given that the grey card I used is 18% and my meter is calibrated for 12% I would expect to be off by at least 1/2 a stop, which means there is still 1/2 a stop unaccounted for. I would therefore have to rate the F55 (mine at least) to approximately 800 ISO, not 1250 ISO as claimed by Sony.
Couple tips to keep in mind if trying this; the angle of your grey card to the light and hence camera can easily give you a full stop in variation so don't make the mistake of shooting the reflection of the light itself in the grey card with the camera. Take the light meter read in the axis of the light, not the camera.
I tried lumisphere up or down without any difference in reading.
Conclusion: given that the grey card I used is 18% and my meter is calibrated for 12% I would expect to be off by at least 1/2 a stop, which means there is still 1/2 a stop unaccounted for. I would therefore have to rate the F55 (mine at least) to approximately 800 ISO, not 1250 ISO as claimed by Sony.
Couple tips to keep in mind if trying this; the angle of your grey card to the light and hence camera can easily give you a full stop in variation so don't make the mistake of shooting the reflection of the light itself in the grey card with the camera. Take the light meter read in the axis of the light, not the camera.
Last edited:
If the meter is calibrated to a 12% card but you are using an 18% card, that will cause the meter to overstate the camera iso rating by 1/2 stop.
Then there are the assumptions which may not be correct, that the lens is rated correctly, the gray card, the meter, the camera. The fact is, none of them have nist traceable certs, how do you assume that 3 are correct, (lens, card, meter) and not the camera?
Doug's method of using the white card and the incident reading mode is the best process because it's measuring the fullest quantity of light, scope, meter and card. But you still can't be absolutely certain because his meter and lens aren't calibrated even if his leader scope is.
I've been rating with my sekonic as well, and from time to time come up with slightly different results depending on which lens, which f-stop, even the color temperature, but overall for my F55, the rating does seem to average around 1250 iso when used with my L398A, which uses no amplification, just a basic photo cell designed for an era when a fast iso was Kodak Tri X Pan 400. When I use that meter, iso800 metering at times has been right, at other times slightly over exposed. So on average with my equipment, if I'm going to use the sekonic, it's safer at 1250. But the most reliable tool is the waveform monitor; the sekonic is helpful for setting up the lights or contrast ratios.
Then there are the assumptions which may not be correct, that the lens is rated correctly, the gray card, the meter, the camera. The fact is, none of them have nist traceable certs, how do you assume that 3 are correct, (lens, card, meter) and not the camera?
Doug's method of using the white card and the incident reading mode is the best process because it's measuring the fullest quantity of light, scope, meter and card. But you still can't be absolutely certain because his meter and lens aren't calibrated even if his leader scope is.
I've been rating with my sekonic as well, and from time to time come up with slightly different results depending on which lens, which f-stop, even the color temperature, but overall for my F55, the rating does seem to average around 1250 iso when used with my L398A, which uses no amplification, just a basic photo cell designed for an era when a fast iso was Kodak Tri X Pan 400. When I use that meter, iso800 metering at times has been right, at other times slightly over exposed. So on average with my equipment, if I'm going to use the sekonic, it's safer at 1250. But the most reliable tool is the waveform monitor; the sekonic is helpful for setting up the lights or contrast ratios.
starcentral
Veteran
Yes Tom I definitely agree with everything you have said.
What I've suggested over on another forum for Sekonic 758c an L508 users (but do check your own model's calibration value in the manual and calculate % grey) is to set your exposure compensation to -0.5EV which is around half a stop and will compensate for the meter's 12% calibration versus 18% grey card.
I also agree there are far too many variables in the chain. When I take meter reads sometimes I can get the same reading with the lumisphere up or down, other times its different as it depends on the light setup. Then there is the angle of grey card to the camera, angle of light to the grey card, then what axis you take the meter read… the list is endless.
An interesting way to test the integrity of your "grey card" or setup of it is to actually use a white card and set it to the appropriate IRE on your waveform monitor and then swap in your grey card - now note where its sitting on your waveform monitor and where it SHOULD BE sitting!
Overall I think if you're getting within 1/2 stop you are lucky. If you are getting "right on" with your meter and camera then I'd actually suggest that something is "wrong" as funny as that sounds but lucky for you that you got a match.
Correct me if I'm wrong but at 2000 ISO "one stop" can be in the single or low double digit foot-candle range… it doesn't take much of anything to throw results off.
What I've suggested over on another forum for Sekonic 758c an L508 users (but do check your own model's calibration value in the manual and calculate % grey) is to set your exposure compensation to -0.5EV which is around half a stop and will compensate for the meter's 12% calibration versus 18% grey card.
I also agree there are far too many variables in the chain. When I take meter reads sometimes I can get the same reading with the lumisphere up or down, other times its different as it depends on the light setup. Then there is the angle of grey card to the camera, angle of light to the grey card, then what axis you take the meter read… the list is endless.
An interesting way to test the integrity of your "grey card" or setup of it is to actually use a white card and set it to the appropriate IRE on your waveform monitor and then swap in your grey card - now note where its sitting on your waveform monitor and where it SHOULD BE sitting!
Overall I think if you're getting within 1/2 stop you are lucky. If you are getting "right on" with your meter and camera then I'd actually suggest that something is "wrong" as funny as that sounds but lucky for you that you got a match.
Correct me if I'm wrong but at 2000 ISO "one stop" can be in the single or low double digit foot-candle range… it doesn't take much of anything to throw results off.
If I understand what you're saying, at lower lighting levels just a few foot candles can represent an f-stop, which is why for measuring sensitivity or rating a camera's max iso, I think it's better to maximize the fullness of the measurement by using the white card at 59% (for slog2), and reading the light in incident mode facing the camera lens from the target.
For real world work, I wouldn't work this way, I'd rate the the camera using the gray card reflectance mode (which might result in a different number, I would verify this for each lighting setup or condition, and meter reflectance off the subject or the gray card for the take.
The irony in all this, is that the F55 has so much latitude, it's inexcusable to miss on exposure with it and I never have. It's when I mix with other cams shooting std gammas with limited DR that I have to be especially careful with.
For real world work, I wouldn't work this way, I'd rate the the camera using the gray card reflectance mode (which might result in a different number, I would verify this for each lighting setup or condition, and meter reflectance off the subject or the gray card for the take.
The irony in all this, is that the F55 has so much latitude, it's inexcusable to miss on exposure with it and I never have. It's when I mix with other cams shooting std gammas with limited DR that I have to be especially careful with.
starcentral
Veteran
I know Mark is getting his hands on a 2nd F5 so I'm curious to see if he gets different ISO ratings between the two, maybe his is off, who knows.
I shot with two F55's recently on a commercial and they were bang on with each other. Using mostly my light meter to set exposure is be shouting f-stops to both camera operators, usually making a minor tweak by 1/2 stop but not always.
When I can work like that I love it for some reason.
I shot with two F55's recently on a commercial and they were bang on with each other. Using mostly my light meter to set exposure is be shouting f-stops to both camera operators, usually making a minor tweak by 1/2 stop but not always.
When I can work like that I love it for some reason.