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Low Light Question: ISO vs Underexposure

Discussion in 'Open Discussion' started by alphasierra, Aug 4, 2011.

  1. alphasierra

    alphasierra Mu-43 Rookie

    16
    Jun 13, 2011
    Melbourne, Australia
    I've got a GF2, and don't really like the images I get above ISO1600 (really prefer to keep it below 800 if I can). But in low light I also try to avoid using the flash, because it seems to suck the soul out of whoever I photograph! So, the solution I came up with (when there wasn't much light) was to keep the ISO down as much as possible, underexpose to keep shutter speed up, then adjust the exposure back (from RAW) in Lightroom as needed. But, some of the recent discussion about exposing to the right got me thinking...

    So I took a set of trial shots: same aperture/shutter, but I used ISO400 underexposed 2 stops, ISO800 underexposed 1 stop, and ISO1600 at 'correct' exposure. I then adjusted these in Lightroom so they were all about the same, and looked at full size. As far as I can tell - the noise in all is about the same! Does this make sense? Is ISO in the camera just digital gain, and does Lightroom just do the same thing in software?

    Can anyone with a bit more experience tell me whether I've been wasting my time fixing images I took at ISO800, when I should just take things at 1600 in the first place? Or, worse, does the camera actually do a better job at 1600 in the first place?

    Sorry if this is already covered somewhere - I did a bit of searching, and couldn't find anything. Thanks for help.
     
  2. GaryAyala

    GaryAyala Mu-43 Legend

    Jan 2, 2011
    SoCal
    Typically, I found through experience, that shooting at a "proper ISO" is superior to underexposing then trying to pull it out in post. I found that noise is better when properly exposed than underexposed.

    I also found that careful metering, (i.e. spot metering on the principal element and adjusting accordingly), helps in low light situations in keeping one's ISO lower.

    On the GF1, (same sensor as the GF2), for my tastes, I find ISO 800 marginally acceptable and above ISO 800 essentially unacceptable due to noise.

    There are many I know who are very skilled with a flash. So skilled that one needs to take a close look to distinguish between flash and non-flash images. I am not one of those skilled flash photogs ... as such I use available light for nearly everything, which is a vicious circle because I never better my crappy flash skills.

    G
     
  3. Hikari

    Hikari Mu-43 All-Pro

    Nov 26, 2010
    +1 with Gary.

    Sensors don't get more sensitive. As you increase ISO, you give the sensor less light. Signal reduces in relation with noise with is fairly fixed. I would shot at what ISO you want.
     
  4. RobWatson

    RobWatson Mu-43 Hall of Famer

    Not to nit pick but less exposure time collects less light irrespective of ISO. The only way to 'fix' low light is to collect more light.
     
  5. Hikari

    Hikari Mu-43 All-Pro

    Nov 26, 2010
    And the camera will reduce the amount of light when you increase ISO. So why would underexposing and changing the ISO have a significant difference on the amount of light reaching the sensor? Exposure IS in relation to ISO.
     
  6. RobWatson

    RobWatson Mu-43 Hall of Famer

    Fixed exposure does not care what ISO is used ... I rarely use auto ISO in low light. Actually I use ISO 200 (optimum for E-P1) so I have the best DR performance (maybe potential is a better term here) and then push the exposure time as much as possible. EV can be pumped up in PP to 'brighten' if needed. Using higher ISO and shorter exposure so as to push EV less in PP will be noisier.

    I really need to resist picking at nits!
     
  7. ~tc~

    ~tc~ Mu-43 Hall of Famer

    Oct 22, 2010
    Houston, TX
    Bigger aperture is the real solution - throw on a 20/1.7, 25/1.4, or 25/0.95 and you'll be exposed properly and <ISO800
     
  8. PeterB666

    PeterB666 Mu-43 Top Veteran

    780
    Jan 14, 2010
    Tura Beach, Australia
    Peter
    Underexposure kills.

    If the subject isn't moving, then use longer exposures and expose correctly for the light. A tripod is your friend.

    Large apertures sometimes work but need to be considered along with depth of field requirements and lens performance.
     
  9. Hikari

    Hikari Mu-43 All-Pro

    Nov 26, 2010
    Is there anything in the OPs post that suggests he is basing exposure on anything else than what the camera is determining? That is the scope of the discussion.
     
  10. alphasierra

    alphasierra Mu-43 Rookie

    16
    Jun 13, 2011
    Melbourne, Australia
    Thanks for the comments - but seem to be getting confusing messages so far! I'm already doing the obvious stuff, using a large aperture and the longest exposure I can handhold (so usually the 20/1.7, and about 1/30th). And although a noisy picture at ISO1600 isn't exactly a work of art, it beats no picture if the event itself is important.

    So, let's say it's a poorly lit room, and there's just not enough light to work at low ISO. Let's say that to get correct exposure straight out of the camera I would need to use ISO1600. My other option is to use ISO800, accept the underexposure, and correct the exposure by 1 stop in Lightroom. Which of these will give me a better result - or is it a draw?
     
  11. RobWatson

    RobWatson Mu-43 Hall of Famer

    OP asking if ISO 800 and under expose is same/better/worse than ISO 1600 (implied the same exposure as at ISO 800 but not under exposed - OP terms). So, yes biasing. I'm not certain how ccd differs from cmos in this respect but I suspect higher ISO will be worse but the practical difference will be hard to tell.
     
  12. GaryAyala

    GaryAyala Mu-43 Legend

    Jan 2, 2011
    SoCal
    I really don't quite understand how this relates to the OP's question.
     
  13. GaryAyala

    GaryAyala Mu-43 Legend

    Jan 2, 2011
    SoCal
    I thought I had answered your question. My experience is that a properly exposed ISO 1600 will deliver less noise than an underexposed ISO 800.

    If there are no other options, then Yes, a noisy image is better than no image at all. (An external flash with tilts and swivel is another alternative to both ISO 1600 and the on-board flash. If the ambient lighting and naturtal looking DOF are important elements to the image ... then ISO 1600 is your only option.)

    Gary
     
  14. alphasierra

    alphasierra Mu-43 Rookie

    16
    Jun 13, 2011
    Melbourne, Australia
    Thanks Gary - that's nice and succinct, and answers my question. I'll abandon the crazy underexposure games, set the ISO as high as needed, and learn to love what results.
     
  15. Djarum

    Djarum Super Moderator

    Dec 15, 2009
    Huntsville, AL, USA
    Jason
    Id say experiment for yourself. My guess is that a properly exposed shot will show less noise in the highlights and midtones at a higher iso.
     
  16. GaryAyala

    GaryAyala Mu-43 Legend

    Jan 2, 2011
    SoCal
    PS- Converting the image to B&W will help "camouflage" noise and make the noise less apparent.

    G
     
  17. B&W noise can make for nice grain, lol
     
  18. RobWatson

    RobWatson Mu-43 Hall of Famer

    Fixed aperture, shutter and light levels ... how to get 'better images'? OP Q in a nutshell? The only options presented are hi ISO and low ISO+PP push. If 'better' means less noise I bet you'll find low ISO+PP push wins. If 'better' means more appealing or pleasing or impacting then that belongs in the eye of the beholder. There is not a 1:1 between noise versus pleasing, etc.

    OP already has a data set so which one is found to be 'better'? The answer lays square in the hands of the questioner.
     
  19. ~tc~

    ~tc~ Mu-43 Hall of Famer

    Oct 22, 2010
    Houston, TX
    I think there was a valid point made above also about "what is a proper exposure".

    If you're in a dark room, do you care that all the darkness is properly exposed, of just the (dimly, but brighter) lit subject?

    You might try setting to spot metering, and then using the exposure compensation to adjust slightly from there.