ISO control vs ND filters

[AStamper]

Forgive my naivete, but I wanted to ask a potentially noob question. I know that Red prides it's self with the low range of its ISO. 800 is the new 320 and so on.

So basic concept, as you raise the ISO, the sensitivity is increased and with it the noise increases, as you lower it the noise disappears.

My question is can you lower the ISO too much, if the light is available, or would a good ND be preferable? I ask because I noticed the Fixed has a built in ND filter and I was surprised. Why switch on the ND instead of lowering my ISO and getting (perhaps imperceptibly) a cleaner picture.

Note: we are for the moment ignoring polarizers as they change image not only act ND.

 

[Evin Grant]

Even at ISO 320 you still need ND to shoot outside with a T stop below F45. Personally I've been rating the MX chip at 500 outdoors for connivence and 800-1000 indoors The new chip is also much more resistant to IR pollution, so you can safely use a 1.2 ND and Pola combined to shoot at F5.6-8 is direct sunlight. More than that and I'd recommend a Hot mirror type filter or combo.

 

[David Mullen ASC]

Once you drop below the native sensitivity of the sensor (around 400 ASA let's say) and rate the camera slower to deal with high light levels (let's say, 50 ASA) you are pushing more highlight information near the clip point. And if you actually underexposed your highlights to compensate and retain detail, you are defacto rating the sensor faster again for all practical purposes.

The "Sunny 16" rule of photography states that in direct sunlight on a clear day, midday, your exposure is f/16 if the value of the ASA rating is the same number as value under the 1/ figure of the shutter speed -- i.e. 50 ASA at 1/50th, 100 ASA at 1/100th, etc.

So you'd need an ND.9 (3-stops) to get 400 ASA down to a manageable 50 ASA equivalent without rerating the sensor, and that still only gets you to an f/16 at 1/50th of a second in direct sunlight. So ND filters are a must-have for day exterior shooting.

 

[Antoine Fabi]

Seems reasonable to think the MX is clean enough to shoot ISO 800 outdoors for wide DR.
What would be the ND match for 1/48 shutter ?

Antoine

 

[Anthony DeRose]

I have not used the new MX sensor and really do not know the most about it. But is it best to shoot with that camera outdoors at ISO 800? I read that you can clip more now at 320 using the new sensor. But if your shooting at a 800 thats a lot of ND you need to put in.

 

[David Mullen ASC]

I was OK at 500 ASA on the M-X Red if I watched the highlights, but there is no getting around needing ND. I never went heavier than an ND1.2 but that's because I was willing to be stopped down somewhat in sunlight, since I was using long lenses. You could always add a Pola to that, but you risk double-reflections sometimes off of bright edges.

 

[Pawel Achtel]

I often use Pancro ND 2.0 plus TRUE POLA plus an ND grad...and still could add a few stops more before neededing to shoot fully opened.

 

[Stephen Strangways]

A sensor clips the highlights when it gets too much light, regardless of ISO setting.

So, if your highlights are clipped at the native sensitivity of ISO 320, you can change to ISO 250 or 125 but your highlights will still be clipped.
You might get a tiny bit cleaner image in terms of noise, but your overall image is darker while your highlights are still clipped, so you've just decreased the dynamic range your camera can capture.
The same applies to DSLRs with native ISO 200 sensors that can be set to ISO 100... you could do it, but all you're really doing is just losing dynamic range.

On the flip side of that, if your highlights are clipped at 320, you can stop down the iris of your lens or add ND filters to let less light in, and get those highlights to a level where they are not clipped.

But... then the rest of your image is too dark. Well, just raise your ISO and it will raise the shadows and midtones, without making the highlights clip. And the joy of the M-X sensor is that you can raise the ISO to 800 without worrying about noise.

It seems counter-intuitive if you're used to film, or analog gain on video cameras and still cameras, but when you're shooting outdoors in bright sunlight with a huge contrast range to your scene, you can raise your ISO and close your iris down or add ND filters to better fit the contrast range of the scene into the range the sensor can handle.

 

[Tim Hole]

We don't have that problem in the UK, we don't have very many bright clear days

From experience of shooting in Poland or Norway during Winters it can be completely nutty trying to expose correctly when shooting snow . Havent shot snow on an MX so can't comment.

 

[Antoine Fabi]

With the MX...

On a sunny day, with two ND.9, i was dialing about f4 to f5.6 at ISO 500.

..without any problem!

The Hot Mirror rested in the lenses case

Incredible this MX...

Antoine