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Thread: Best ISO for A850

  1. #1
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    Best ISO for A850

    In a studio situation and shooting raw what Iso performs best on a A850?

  2. #2
    Tony Beach
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    Re: Best ISO for A850

    I've done some recent experiments with adjusting the exposure relative to the ISO and found a distinct non-linearity below ISO 200. At middle gray WB gain was constant at all ISOs, but at near maximum saturation (ETTR) the red and blue channels dropped down noticeably relative to the green channel going from ISO 200 to 160. This means you will have some color shifts below ISO 200.

    Also, headroom in the RAW ISO 100 files appears to be no greater than it is in the ISO 160 files. My conclusions are therefore that ISO 125 and 100 are really for getting flash sync to work with JPEGs, and if you are shooting RAW at ISO 160 then you should be alright if you make sure to set WB based on the luminance value of the subject's faces.

    For better shadow detail ISO 320 works best on the A850. While that shouldn't be a studio issue, I still find that to be the optimal ISO for the A850 and I use it as my default even with controlled lighting. I personally feel comfortable using any ISO from 200 to 500; and while 200 is smoother than 320, some of that smoothness comes at the price of blotchier shadow detail, but if you are keeping within 2 1/2 stops of middle gray then I don't think you will have any issues in the shadows at those lower ISOs.

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    Re: Best ISO for A850

    Thanks,
    I am a bit confused however regarding setting the white balance based on Luminance of the faces?
    Last edited by barry685; 2nd January 2011 at 12:51.

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    Re: Best ISO for A850

    Assuming the 850 is like the 900, I try to stick to ISO320 if I can. If I have too much light for that, I will drop down to ISO100.

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    Re: Best ISO for A850

    I followed a lot of the discussion of the pros/cons of 200 vs 320, even 160 over a year or so...and I fully accept the views of the RC developers (and Tony here) on the matter - for technical purity.

    They also advise not to underexpose...and of course you are closer to that with 320, all other things being equal.

    Many nature shooters want smoothness (sky, water, clouds etc.) as a primary goal, me too, so 200 it is for me. For some small time I did shoot both and I feel that the difference was swamped by other factors - this is in harsh light testing the limits of the sensor's DR. I don't often have the luxury of using ETTR, a colour compromising technique I dislike in any case, for modern sensors. But then I feel shadow detail is overstated as colour is a mid-tone phenomenon, so maybe take my comments with some salt! I see very few viewers exclaiming that an otherwise sound A900 image lacks shadow detail...but they generally love the colours.

    I do sometimes see some red misbehaviour using the PS eyedropper in deep shadows, and very occasionally it is a concern, but most often not, in real terms rather than what one sees for luminance values in the 0-30 range - in my experience. I have never seen objectionable blotchiness with the naked eye, and feel one would have to be really digging hard into the shadows in post to do so, either for a probably vain rescue bid or to create an artifical tonal relationship in the image from a single exposure. For shadow recovery (and much else) I use Tony Kuyper's luminosity masks and blend modes (screen in this case).

    To round off, over-exposure hurts any digital quite badly if colour integrity and clean neutrals are goals, ETTR notwithstanding; and (in the A900) some noise is never far off with higher than standard ISOs, given inevitable exposure misses/compromises. For the outdoors in any case.

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    Re: Best ISO for A850

    ISO lower than 320 will tend to block up the shadows more readily. It's not always obvious, but when it does rear its head it's regrettable. On a recent trip to Yosemite I went to ISO 100 to get a slow shutter for a waterfall, then forgot to set it back. On some subsequent high-contrast scenes I ended up with some ugly transitions into shadow areas that are much smoother on the ISO 320 shots.

    It depends on many factors, there is certainly no need to change if what you are doing works for you!
    α900+VG|F20|2xF58|16-35,24-70,135Z|STF|70-400G|50,85 1.4|16,20,28,100M,80-200APO f/2.8|28-135|500f/8|1x-3xMacro|2xMFC-1000|Tiltall+RRS, Bellows, etc.

  7. #7
    Tony Beach
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    Re: Best ISO for A850

    Quote Originally Posted by barry685 View Post
    Thanks,
    I am a bit confused however regarding setting the white balance based on Luminance of the faces?
    Here's an example of what I'm referring to:



    Note the edge of the CC24 chart on the right. You get different WB readings when you select different patches, with the best choice being the patch that most closely matches the subject's face (in this instance, my face). With ISO 160 (on the left) the color shifts become more problematic with relatively small changes in the WB selected, whereas they are more stable using ISO 320 (on the right).

    I prefer the skin tones on the ISO 320 shot here, and that was consistently the case from the several test shots I took. Your lighting may be different, the profiling of your RAW converter may be different, what you prefer may be different; so strictly speaking for myself based on using Capture One and my preferences, I would repeat that I would avoid going below ISO 200 -- but YMMV.

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    Re: Best ISO for A850

    Tony, you don't look too happy about your results there...
    α900+VG|F20|2xF58|16-35,24-70,135Z|STF|70-400G|50,85 1.4|16,20,28,100M,80-200APO f/2.8|28-135|500f/8|1x-3xMacro|2xMFC-1000|Tiltall+RRS, Bellows, etc.

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    Re: Best ISO for A850

    Quote Originally Posted by Tony Beach View Post
    I've done some recent experiments with adjusting the exposure relative to the ISO and found a distinct non-linearity below ISO 200. At middle gray WB gain was constant at all ISOs, but at near maximum saturation (ETTR) the red and blue channels dropped down noticeably relative to the green channel going from ISO 200 to 160. This means you will have some color shifts below ISO 200.

    Also, headroom in the RAW ISO 100 files appears to be no greater than it is in the ISO 160 files. My conclusions are therefore that ISO 125 and 100 are really for getting flash sync to work with JPEGs, and if you are shooting RAW at ISO 160 then you should be alright if you make sure to set WB based on the luminance value of the subject's faces.

    For better shadow detail ISO 320 works best on the A850. While that shouldn't be a studio issue, I still find that to be the optimal ISO for the A850 and I use it as my default even with controlled lighting. I personally feel comfortable using any ISO from 200 to 500; and while 200 is smoother than 320, some of that smoothness comes at the price of blotchier shadow detail, but if you are keeping within 2 1/2 stops of middle gray then I don't think you will have any issues in the shadows at those lower ISOs.
    Totally agree with this using an A900.

    -Marc

  10. #10
    Tony Beach
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    Re: Best ISO for A850

    Quote Originally Posted by Dave_Anderson View Post
    Tony, you don't look too happy about your results there...
    Yeah, I'm quite possibly the world's worse model. One the bright side, I can strike that pose over and over again.

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    Re: Best ISO for A850

    Tony, I see that... until I read the text I thought it was the same capture, different processing.

    Note that the colorchecker chart greys may not be as neutral as we may hope they are. Sometimes this is because we select a pixel that is "noise", but there is also some inconsistency in the charts. See the results of a test that I ran a while back - same capture, WB set at locations indicated by red cross. Exposure was 1/15(to catch four full AC cycles in the artificial light), ISO was 400. None of the chart squares are truly neutral and there is a subtle shift between squares. I was careful to avoid "noise" with the eyedropper.

    α900+VG|F20|2xF58|16-35,24-70,135Z|STF|70-400G|50,85 1.4|16,20,28,100M,80-200APO f/2.8|28-135|500f/8|1x-3xMacro|2xMFC-1000|Tiltall+RRS, Bellows, etc.

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    Re: Best ISO for A850

    Dave, in my experience, it does help to turn the noise reduction on when using the eyedropper.
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    Re: Best ISO for A850

    Ed, I was thinking of another test. I went back and looked at these in LR and I had cranked NR way up(far beyond the norm) until the patches were even with no noise.
    α900+VG|F20|2xF58|16-35,24-70,135Z|STF|70-400G|50,85 1.4|16,20,28,100M,80-200APO f/2.8|28-135|500f/8|1x-3xMacro|2xMFC-1000|Tiltall+RRS, Bellows, etc.

  14. #14
    Tony Beach
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    Re: Best ISO for A850

    Quote Originally Posted by edwardkaraa View Post
    Dave, in my experience, it does help to turn the noise reduction on when using the eyedropper.
    A trick I use is to shoot the colorchecker out of focus.

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