Tag Archives: rating

A7, FX3, FX6, PXW-FX9

Which Sony ISO RatingS Are Correct?

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In the course of my tests with the FX3 and comparing it with the FX6 and FX9 I discovered a strange anomaly with the FX3 and A7SIII ISO ratings when compared to the FX6 and FX9. 


The FX3’s default picture profile is PP11 and S-Cinetone. If you have an FX6 or FX9 these cameras also default to S-Cinetone in SDR mode. In the FX6 and FX9 the base ISO for S-Cinetone is 320 ISO. Therefore you would assume that if you also set the A7SIII or the FX3 to 320 ISO and expose all the cameras the same, same aperture, shutter etc that the exposures would match.

BUT THE EXPOSURES DON’T MATCH!!

FX6-Exposure_1.1.1-600x338 Which Sony ISO RatingS Are Correct?
The FX6 at 320 ISO, 1/50th shutter, S-Cinetone.

 

FX3-Exposure_1.2.1-600x338 Which Sony ISO RatingS Are Correct?
The FX3 with the same 320 ISO, 1/50th shutter and S-Cinetone. It’s clearly brighter.



The FX3 and the A7SIIII are just over 1 stop brighter than the FX6 and FX9 when all the exposure settings are matched. I tested all the cameras with the same lens to ensure this wasn’t a lens issue, but it isn’t the lens.

FX3-S-Cinetone-scopes-copy-1 Which Sony ISO RatingS Are Correct?
FX3 S-Cinetone is brighter compared to the FX6/FX9 and over exposed according to my light meter by just over 1 stop. The white of the white card should be at approx 83% and my skin tones are well into the highlight roll off and looking flat as a result.

 

FX6-s-cinetone-scopes-copy Which Sony ISO RatingS Are Correct?
The FX6’s exposure much more closely matches my light meter and is only a fraction of a stop under with the white card just touching the 83% exposure I would normally expect with S-Cinetone.

 

 

Screenshot-2021-02-26-at-13.16.16 Which Sony ISO RatingS Are Correct?
Here’s the FX3 again, the whites are much, much too bright when exposed against my light meter, even the middle grey is over 60%. The MM+0.7 indication means the camera thinks it is over exposed.

 

Screenshot-2021-02-26-at-13.16.49-copy Which Sony ISO RatingS Are Correct?
And the FX6 with exactly the same settings and the same lens matches my light meter very closely, white is around 83% and middle grey around 45%, as I would expect. Something odd is going on here, it’s not just my light meter it’s something else as the cameras should at least match, even if they don’t agree with the light meter.



I then went on to test other gamma/picture profile settings and I found a just over 1 stop difference between the FX3 and my FX6/FX9 in any similar combination EXCEPT S-LOG3!

Screenshot-2021-02-26-at-13.14.18 Which Sony ISO RatingS Are Correct?
The FX3 shooting S-Log3 now it matches my light meter very closely and the exposure is add I would expect.

 

Screenshot-2021-02-26-at-13.14.41 Which Sony ISO RatingS Are Correct?
This is the FX6 set exactly the same as the FX3 shooting S-Log3. Now they both match and now the both provide the same exposure and closely match my light meter.



When using Picture Profile 2 on the FX3 which is uses Sony’s “Still” gamma and then using the “Still” Profile on the FX6 there is a difference of around 1 stop. If I set the FX3 to PP3 (ITU-709) and the FX6 to ITU-709 then the difference is again around 1 stop, in every case the FX3 is brighter except when you select S-Log3 where the FX3 and the FX6/FX9 match almost perfectly!

I find this very strange. They should not be different. My light meter suggests to me that the FX6/FX9 are correct.

Comparing to my light meter I believe the FX6/FX9 ratings to be correct and the FX3 to be between 1 and 1.3 stops brighter than it should be when using gammas that are not S-Log3. What I really don’t understand is why the FX3/A7SIII match the FX6/FX9 when using S-Log3 but do not match when using the other profiles, normally I would expect to see a consistent offset. This further makes leads me to be sure this is not a problem with my light meter, but something else.

I would love to hear from anyone else that’s able to take a look at the ISO ratings of the A7SIII and compare it with an FX6 or FX9.

The bottom line is – DON’T EXPECT TO PUT THE SAME EXPOSURE SETTINGS INTO BOTH AN FX3 AND AN FX6/FX9 AND GET THE SAME RESULTS, because you won’t, unless you are using S-Log3, then they match. 

Also in the clip metadata I found that 0dB for S-Cinetone is 100 ISO, and whether this is a coincidence or not, if I set the FX3 to 100 ISO and the FX6 to 320 ISO and then match shutter speed and aperture then the exposures are very close.

This one has left me confused!!!!

PXW-FX9

FX9 ISO Rating Confirmation Test

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While I had the light meter and exposure test chart out for the FX6 I decided to do the same exposure level confirmation test for the FX9. No nasty surprises, the FX9’s ISO ratings certainly appear to be correct. Again using a DSC Labs exposure reference chart with 18% middle grey and 90% white plus my trusty Sekonic I tested the FX9 at both 800 ISO and 4000 ISO and my light meter and the camera were in good agreement. At 800 ISO the light meter was saying f4.01 while the camera was at f4, I suspect this tiny difference is probably down to transmission losses in the lens.

FX9-Exposure-Test-800_1.2.1 FX9 ISO Rating Confirmation Test
FX9 Exposure rating test at 800 ISO.
FX9-Exposure-Test-4000_1.1.1 FX9 ISO Rating Confirmation Test
FX9 Exposure ISO rating test at 4000 ISO.
FX6

FX6 ISO rating Confirmation Test

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I have already done this a few times, but having seen some other tests suggesting the FX6’s ISO ratings were incorrect. So I decided to re-confirm my previous findings, which is that the ratings Sony give their cameras is correct. For the test I used a DSC labs exposure calibration chart which is an extremely accurate 18%/90% reflectivity chart and my trusty Sekonic light meter. As you can see at both 800 ISO and 12,800 ISO the light meters indicated exposure settings perfectly match the camera’s ISO ratings, shutter speed and aperture. For the 12,800 ISO test, as my light meter doesn’t go up to 12,800 ISO  I set the light meter to 6400 ISO which is one stop lower than the cameras 12,800. The light meter indicated f11 which is one stop below the f16 required by the camera – confirming that the ISO rating is correct.

FX6-Exposure-test-800_1.2.1 FX6 ISO rating Confirmation Test
800 ISO FX6 exposure calibration test.
FX6-Exposure-test-12800_1.1.2 FX6 ISO rating Confirmation Test
FX6 12,800 ISo exposure calibration test.
cinematography, Shooting Tips

ISO and EI – using the right terms makes what you are doing easier to understand.

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ISO and EI are different things and have different meanings. I find that it really helps understand what you are doing if you use the terms correctly and understand exactly what each really means.

ISO is the measured sensitivity of film stock. There is no actual direct equivalent for electronic cameras as the camera manufacturer is free to determine what they believe is an acceptable noise level. So one camera with an ISO of 1000 may be a lot more or less sensitive than another camera rated at 1000 ISO, it all depends on how much noise the manufacturer things is acceptable for that particular camera.

Broadly speaking on an electronic camera ISO is the number you would enter in to a light meter to achieve the a normally exposed image. It is the nearest equivalent to a sensitivity rating, it isn’t an actual sensitivity rating, but it’s what you need to enter into a light meter if you want to set the exposure that way.

EI is the Exposure Index. For film this is the manufacturers recommended best setting for your light meter to get the best results following the standard developing process for the chosen film stock. It is often different from the films true sensitivity rating. For example Kodak 500T is a 500 ISO film stock that has an EI of 350 when shooting under tungsten light. In almost all situations you would use the EI and not the ISO.

On an electronic camera EI normally refers to an exposure rating that you have chosen to give the camera to get the optimum results for the type of scene you are shooting. ISO may give the median/average/typical exposure for the camera but often rating the camera at a different ISO can give better results depending on your preferences for noise or highlight/shadow range etc. If you find exposing a bit brighter helps your images then you are rating the camera slower (treating it as though it’s less sensitive) and you would enter your new lower sensitivity rating into your light meter and this would be the EI.

Keeping EI and ISO as two different things (because they are) helps you to understand what your camera is doing. ISO is the base or manufacturer sensitivity rating and in most (but not all) log or raw cameras you cannot change this.

EI is the equivalent sensitivity number that you may choose to use to offset the exposure away from the manufacturers rating.

If you freely interchange ISO and EI it’s very confusing for people as they don’t know whether you are referring to the base sensitivity rating or a sensitivity rating that is not the base sensitivity but actually some kind of offset.

If you have a camera with an ISO rating of 2000 and you say “I’m shooting at 800 EI” then it’s clear that you are using a 1.3 stop exposure offset. But if you just say “I’m shooting at 800 ISO” it is less clear as to exactly what you are doing. Have you somehow changed the cameras base sensitivity or are you using an offset? While the numbers used by EI and ISO are the same, the meaning of the terms ISO and EI are importantly different.

cinematography, PMW-F55, PXW-FS5, PXW-FS7, Technology

Why are Sony’s ISO’s different between standard gammas and log?

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With Sony’s log capable cameras (and most other manufacturers) when you switch between the standard gamma curves and log gamma there is a change in the cameras ISO rating. For example the FS7 is rated at 800 ISO in rec709 but rated at 2000 ISO in log. Why does this change occur and how does it effect the pictures you shoot?

As 709 etc has a limited DR (between around 6 and 10 stops depending on the knee settings) while the sensor itself has a 14 stop range, you only need to take a small part of the sensors full range to produce that smaller range 709 or hypergamma image. That gives the camera manufacturer some freedom to pick the sweetest part of the sensors range. his also gives some leeway as to where you place the base ISO.

I suspect Sony chose 800 ISO for the FS7 and F5 etc as that’s the sensors sweet spot, I certainly don’t think it was an accidental choice.

What is ISO on an electronic camera? ISO is the equivalent sensitivity rating. It isn’t a measure of the cameras actual sensitivity, it is the ISO rating you need to enter into a light meter if you were using an external light meter to get the correct exposure settings. It is the equivalent sensitivity. Remember we can’t change the sensor in these cameras so we can’t actually change the cameras real sensitivity, all we can do is use different amounts of gain or signal amplification to make the pictures brighter or darker.

When you go switch the camera to log you have no choice other than to take everything the sensor offers. It’s a 14 stop sensor and if you want to record 14 stops, then you have to take 100% of the sensors output. The camera manufacturer then chooses what they believe is the best exposure mid point point where they feel there is an acceptable compromise between noise, highlight and lowlight response. From that the manufacture will get an ISO equivalent exposure rating.

If you have an F5, FS7 or other Sony log camera, look at what happens when you switch from rec709 to S-Log2 but you keep your exposure constant.

Middle grey stays more or less where it is, the highlights come down. White will drop from 90% to around 73%. But the ISO rating given by the camera increases from 800ISO to 2000ISO. This increased ISO number implies that the sensor became more sensitive – This is not the case and a little missleading. If you set the camera up to display gain in dB and switch between rec709 (std gamma) and S-Log the camera stays at 0dB, this should be telling you that there is no change to the cameras gain, no change to it’s sensitivity. Yet the ISO rating changes – why?

The only reason the ISO number increases is to force us to underexpose the sensor by 1.3 stops (relative to standard gammas such as rec709 and almost every other gamma) so we can squeeze a bit more out of the highlights. If you were using an external light meter to set your exposure if you change the ISO setting on the light meter from 800 ISO to 2000 ISO  the light meter will tell you to close the aperture by 1.3 stops. So that’s what we do on the camera, we close the aperture down a bit to gain some extra highlight range.

But all this comes at the expense of the shadows and mid range. Because you are putting less light on the sensor if you use 2000 ISO as your base setting the shadows and mids are now not as good as they would be  in 709 or with the other standard gammas.

This is part of the reason why I recommend that you shoot with log between 1 and 2 stops brighter than the base levels given by Sony. If you shoot 1 stop brighter that is the equivalent to shooting at 1000 ISO and this is closer to the 800 ISO that Sony rate the camera at in standard gamma.  Shooting that bit brighter gives you a much better mid range that grades much better.