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Old 10-12-2011, 12:13   #1 (permalink)
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RAW question

When I increase the exposure on a RAW file am I doing the same thing as increasing the ISO in the camera? If so why can I only adjust around two stops either side?
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Old 10-12-2011, 13:25   #2 (permalink)
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Re: RAW question

I imagine that beyond that point there simply isn't enough information recorded for photoshop to process, i.e. more than 2 stops overexposed you probably just have a wall of white pixels.
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Old 10-12-2011, 13:35   #3 (permalink)
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Re: RAW question

In Lightroom you can do up to four stops under or over, so maybe it is a software thing.
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Old 10-12-2011, 16:49   #4 (permalink)
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Re: RAW question

I'm not sure they are the same things - I always thought ISO affected the sensitivity of the sensor and Exposure alters the quantity of light and/or the time the light is available. As Dabs says I would imaging it is the software, either in camera or PC, which will dictate the number of stops.
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Old 10-12-2011, 17:40   #5 (permalink)
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Re: RAW question

Increasing the exposure does nor effect the ISO. If you took the photo at say 100 iso and then increased the exposure by one or two stops this will just lighten the picture and the "noise or grain " will be the same. But if you set the camera for say 800 iso the effect will be the same except that 800iso will always have more noise than 100 iso. Having said that if you alter the exposure in software over the top it can cause grain an other effects, better to get it right at the time.
Hope this helps.

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Old 10-12-2011, 18:51   #6 (permalink)
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Re: RAW question

Thanks for the replies.

My line of thought was is it going to be any advantage underexposing (primarily to up the shutter speed) then correcting the RAW image rather than increasing the ISO. Maybe I should do a series of tests

This occurred to me yesterday, sat in a hide, freezing cold, stormy dull weather, wishing the ducks would stay still rather than going up and down like manic corks. Maybe it was just the first stage of frostbite setting in?

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Old 10-12-2011, 22:02   #7 (permalink)
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Re: RAW question

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Originally Posted by jake View Post
My line of thought was is it going to be any advantage underexposing (primarily to up the shutter speed) then correcting the RAW image rather than increasing the ISO. Maybe I should do a series of tests
Although fairly new to digital, I have been running various experiments to understand for myself and I believe that the proposal above will more often give you more noise in difficult light. What I have found to be useful is to use a higher ISO than expected, very slightly overexpose it and darken it in the processing. As long as highlights are not burned out. Although the grain will be slightly higher the noise tends to be suppressed through darkening. From this point it's a matter of choice as to whether you want grain or noise, and I find grain easier to deal with (at the moment). So if you're wanting 1/200sec but you have ISO-400 with 1/100sec, I would go to ISO-1000 with 1/200sec. Which is effectively 1/3 stop or maybe as much as 2/3 stop overexposed on subject. These is purely personal and probably dependent on camera, software available, and how much you want to crop I suspect.
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Old 10-12-2011, 23:02   #8 (permalink)
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Re: RAW question

Thanks for the input Graham.
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Old 10-12-2011, 23:55   #9 (permalink)
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Re: RAW question

Quote:
Originally Posted by jake View Post
Thanks for the replies.

My line of thought was is it going to be any advantage underexposing (primarily to up the shutter speed) then correcting the RAW image rather than increasing the ISO. Maybe I should do a series of tests

This occurred to me yesterday, sat in a hide, freezing cold, stormy dull weather, wishing the ducks would stay still rather than going up and down like manic corks. Maybe it was just the first stage of frostbite setting in?
Your sensor can capture around 11 stops of dynamic range. If we assume that the scenes to be captured is 11 stops then you can just capture the entire dynamic range. Adobe Raw will compress to a lower dynamic range so you need to decide what you want in your final image. You can bring the extremes of the highlights into play by using recover or selectively applying the brush with exposure or using the graduated filter. You can pull shadow detail in by using the fill light or again selective applying the exposure brush. By use of the editing controls, you should be able to recover the entire 11 stops in your final image.

If you instead under exposed by 2 stops then you will lose the darkest 2 stops of shadow detail and will never be able to recover it because you did not capture it. You must expose correctly to cover the entire dynamic range of the scene.

Interestingly, if the scene was much lower dynamic range than the sensor say 7 stops then you do have spare dynamic range so could do what you propose though I am not sure there is much to gain from this.
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Old 13-12-2011, 14:53   #10 (permalink)
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Re: RAW question

Quote:
Originally Posted by jake View Post
When I increase the exposure on a RAW file am I doing the same thing as increasing the ISO in the camera?
Yes and no!

Increasing the ISO increases the sensitivity of the sensor, so dark areas will reflect the increased detail. But, as has been pointed out, increasing the exposure of a RAW might bring up details but if the area's clipped then no amount of exposure increase will achieve detail

Quote:
Originally Posted by jake View Post
If so why can I only adjust around two stops either side?
It appears to be a bit arbitrary as to what the limits of the software will be, like exposure compensation on a camera - for years I had the benefit of +/- 3.0 stops and then I "upgraded" to a "better" Canon camera (from my Sigma housebrick) and had to make do with +/- 2.0 (which often isn't enough). Luckily, even Canon gave in to demand and put +/- 3.0 on the 7D!

Personally, I always keep my ISO down as low as possible, in order to retain minimum noise in my detail. If necessary I'll shoot two images, one with adjusted exposure compensation and blend the result - landscape only though!
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Old 13-12-2011, 17:10   #11 (permalink)
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Re: RAW question

Thanks for the input guys
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