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  1. #1 ISO 
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    As a former (analog) stills photographer I am used to the film stock having a light sensitivity by itself. When there was less light it was possible to underexpose the film by a few f stops and over-develop it, thereby getting an ok result although more grainy. The digital sensors of today are a different matter and I'm not fully comprehending how manipulating ISO in different ways is affecting the imagery. Also I have heard that different camera manufacturers use ISO differently.
    I understand we have the sensor and it's sensitivity and I believe changing ISO does alter the position of neutral grey, up or down towards the limitation of the dynamic range, so I believe changing the ISO actually decreases the dynamic range. What I have difficulty understanding is if there is any difference in changing the ISO in-camera or in the post production, as well as if there is a difference between changing the ISO in post or changing the exposure in the post. Is there a better or worse way to handle over or underexposed images in regard to this while correcting the levels in post?
    Some early video cameras had a +6 db switch, an electronic boost similar to over developing film. Do modern video cameras handle it the same way or are we just cranking it up in the post?

    I would be happy to get some more input in regard to this and to understand if different manufacturers handle ISO differently, and if so, how. Thank you.
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  2. #2  
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    I recommend starting with a base ISO of 800 and shooting some exposure tests, then deciding for yourself what 'ISO' to use, based on what you see and prefer with your own eyes (in terms of noise on the one end and clipping point on the other). Then meter and light and set your aperture and shutter-speed to suit, just like you would when shooting analog.

    Your own exposure tests will also show you how much you can 'push' and 'pull' your 'digital negative' in post, after you've captured and locked in your actual exposure (you don't actually change your exposure in post). Imo, regardless of what ISO/light level/aperture/shutter-speed combination you choose as your actual exposure, once you get more than a couple of stops away from it (under or overexposing) you'll be at the limit of what you can easily correct in post.

    That's the short answer, do some tests and then shoot it like it was film.
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  3. #3  
    If shooting raw you capture what the senor sees. That means that settings like iso, tint, kelvins, contrast settings and such are all left open to be adjusted at a later stage. What setting for these parameters you set in camera has no effect what so ever on the quality of your capture. Adjusting them is like turning the dials on you monitor or video tap when shooting film.

    The only thing that has effect on the actual capture is:
    Frame rate.
    Shutter speed.
    Resolution.
    Compression rate.

    So shooting raw is very much like shooting film. Where resolution and compression rate can be compared to different film stocks.

    So iso just a logaritmic post digital gain. and tint and colortemp is just different gain levels for different color chanels.

    Now you could talk about cameras native iso, what iso setting that gives a mid gray / or what iso level that balance the best between noise in lowlights and highlight protection. But this is a moving target as the level of what is acceptable noise levels vary with users, mastering formats, comprsion rates and what type of content is shot. If shooting highress glosy prints you want to expose so you can develop your image at a very low iso level and when shooting for small res web files you run with a way higher iso without worries as the noise will not be visable from the high downsampling the image will go trough.

    Also there is cameras like Gemini that has dual ”native isos” or Low light and highlight modes. Gemini hs a function where the camera is gained at the sensor level in LL mode it gives cleaner black as its moves the DR towards the low end but it also narrows the DR a bit. So you could say that gemini is equiped with two different film stocks.
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  4. #4  
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    Björn, if I understand you correctly then lowering ISO would mean less grain than using "nominal" ISO? Is that really right? Or is it same grain as "nominal" but with a lower dynamic range?
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  5. #5  
    Quote Originally Posted by Andi Loor View Post
    Björn, if I understand you correctly then lowering ISO would mean less grain than using "nominal" ISO? Is that really right? Or is it same grain as "nominal" but with a lower dynamic range?
    Again as iso is digital gain the more gain you add when developing your capture the more visble noise. If you pull gain/iso to zero your imGe is black which is zero noise. If goibg the other way and lift iso you noise will be more and more visable.

    But if you expose your image so the lowlights looks good when developing at 50iso you run a greater risk at burning out your highlights compared to if you for example expose so that your lowlights look god at 1000 iso as such lower exposure gives more room for your highlights.
    Björn Benckert
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  6. #6  
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    Interesting. So nominal does have more grain than lower settings but optimal dynamic range.
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  7. #7  
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    In case you haven't seen it, Red offers a brief and relatively clear on how ISO works in their cameras here:

    https://www.red.com/red-101/iso-speed-revisited
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  8. #8  
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    Thank you, that article did explain a lot. I was wrong in assuming that the dynamic range decreases. It doesn't. It's just that it shifts so that more of the range is used above or below midpoint. They describe it very well as a balance between clipped highlights and noise in the darks. The one thing I didn't get answered is if changing ISO or exposure settings (+ or - f-stop) in post production is actually doing the same thing.
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  9. #9  
    Quote Originally Posted by Andi Loor View Post
    Thank you, that article did explain a lot. I was wrong in assuming that the dynamic range decreases. It doesn't. It's just that it shifts so that more of the range is used above or below midpoint. They describe it very well as a balance between clipped highlights and noise in the darks. The one thing I didn't get answered is if changing ISO or exposure settings (+ or - f-stop) in post production is actually doing the same thing.
    I cannot answer your 2nd question without reading the source code. However, to further reinforce your understanding of ISO in the RED world using your knowledge of film, re-read Ansel Adams' books on the Zone System. Nearly 100 years ago he worked out precisely the concept of exposing to achieve a proper balance of tonal ranges that could then be further manipulated (or rebalanced) in the printing process. Grain doesn't get physically bigger or smaller based on emulsion speed, but digital noise and highlight clipping are real phenomena that must be taken into account. If you want details in shadows, you must hit the sensor with enough light to expose the shadows above whatever noise level you set as acceptable. If you want details in the highlights, you must at all costs prevent the sensor from clipping in the highlights. If the DR in your scene is too wide for a single shot to manage it all, look at HDRx or hire lights, flags, and other tools of the trade. Whatever you do, don't just expose in the middle and hope for the best. Be intentional, and let your craft help you realize your intentions.
    Michael Tiemann, Chapel Hill NC

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  10. #10  
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    Quote Originally Posted by Andi Loor View Post
    The one thing I didn't get answered is if changing ISO or exposure settings (+ or - f-stop) in post production is actually doing the same thing.
    I have to confess that my understanding of what's going on in the background when you adjust ISO in an R3d in post is sketchy. However, one thing I take from that "ISO speed revisited" article is that the ISO you set at the time of capture DOES influence how the material is compressed. So the entire dynamic range will be captured in an R3D workflow, but I gather that the allocation of data to each "level" of that dynamic range will be affected by where you place your middle gray. And this is why (to quote that article):

    "In practice, a higher ISO setting will provide more insurance against clipped highlights, and when highlights do clip, the transition to clipping will typically appear less abrupt. A lower ISO setting will decrease the appearance of noise, particularly within the shadows."

    Someone else correct me if I'm wrong on this-- there is a lot about ISO that can feel counterintuitive when coming from a different system.
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