ISO question

Discussion in 'Digital Photography' started by HE15MAN, Jul 12, 2010.

  1. HE15MAN macrumors 6502a

    HE15MAN

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    #1
    This is one thing I havent figured out yet. How do you really know what ISO to shoot with.

    100-200 Sunny
    400-800 Cloudy
    800+ Overcast is what I was told.

    I am using a T2i
     
  2. MichaelJunge macrumors newbie

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    Jul 9, 2010
    #2
    Part of the issue is that the answer is usually "it depends".

    ISO is only one piece of the 3-part exposure triangle: ISO, aperture, shutter speed.

    Even in low, low light, you might have a 100 ISO, with a long slow shutter, small aperture (and a tripod!). Depends on the result you want.

    I default to 100 ISO, and move upward from there if I need to. With my 40D I rarely go over 400 ISO - too much noise in the image for my liking.
     
  3. silvrbullet macrumors regular

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    Jun 19, 2009
    #3
    The ISO is the last thing you want to adjust.

    Pick your aperture based on what you want your DOF to be, then adjust your shutter speed accordingly. If you can't get your shutter speed to be faster than 1/focal length, increase your ISO.

    I would always leave it @ 100, unless you need it higher.
     
  4. HE15MAN thread starter macrumors 6502a

    HE15MAN

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    #4
    Can you explain this part more? So if say I am using a Canon 100-400 in AV mode at 350mm, the shutter speed should be over 1/350 ? If not, raise the ISO and it will be ok?
     
  5. ManhattanPrjct macrumors 6502

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    #5
    Buy one of Bryan Peterson's books (Understanding Exposure, or the new "Field Guide").

    You will keep it forever, it's easy to read, lots of pictures and examples, and he can explain things like ISO better than anybody.
     
  6. Edge100 macrumors 68000

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    #6
    It's very simple.

    Use the lowest ISO setting you can that allows you to use the aperture and shutter speed that you need.
     
  7. HE15MAN thread starter macrumors 6502a

    HE15MAN

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    #7
    I just started reading it a few minutes ago. I just finished his book Understanding Digital Photography :)
     
  8. leighonigar macrumors 6502a

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    #8
    That's what he meant. Higher ISOs come at the expense of image quality (noise etc.) so generally you want to use the lowest one you can. When you're handholding a camera photographs tend to be blurred when the shutter speed is too low. For a static subject, like a mountain with a full-frame camera this tends (or tended in the days of film) to be visible at about 1/the focal length of the lens. So I could shoot a 50mm at 1/50 seconds and be pretty confident of a sharp shot. Personally with a crop camera I try to shoot at 1/effective focal length, but not everybody is the same.

    Clearly if you're shooting a moving subject or want blur (say, when shooting a waterfall) you have other concerns.
     
  9. HE15MAN thread starter macrumors 6502a

    HE15MAN

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    #9
    Thank you! Yea I enjoy shooting wildlife, birds, and nature scenery, so it seems I am in for a handful of trouble!
     
  10. snberk103 macrumors 603

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    #10
    The best answer is to figure it out yourself.... but I don't mean that in a negative way (no pun intended... :)).

    Set up series of shots in different lighting conditions (sunny, middle, open shade, dark, etc) and shoot the same scene with your fastest, slowest, and a middle ISO. Then compare the results.

    The generally accepted wisdom is that image quality degrades the faster the ISO, but that is necessarily true. The quality of the image changes from fast to slow ISO, and most people will find images taken at high ISOs to be less sharp, but strictly speaking - it is neither a better or worse change - it is merely a change. In some cases the effect may be used the make the picture stronger.

    In the case of film, using a higher ISO also meant more dynamic range. I don't know if this is true of digital - (but now that I've thought of it, I'm going to experiment and figure that out.)

    Like most things in photography, it's something that is best learned by doing..... so do ask these questions to get started with the answer, but then go and see what happens for yourself.

    Good Luck.
     
  11. leighonigar macrumors 6502a

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    #11
    Agreed. And also 'negative'... ha!

    I can't speak for film, I tended to stick to relatively tame ISOs and not really worry about dynamic range (I was young and foolish then). With DSLRs however, generally the broadest DR is obtained with the lowest ISO. Excepting forced low ISOs which some cameras have, or used to have anyhow.
     
  12. mtbdudex macrumors 68000

    mtbdudex

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    #12
    +1 on what others have said, fix ISO at 100 and adjust aperture/speed to get correct exposure.

    My only thought is the T2i has ability to have auto ISO with some fixed upper limit. I'd be curious if you set the upper limit to 400 will the camera select 100 always by default and only go to 200/400 as needed and then show under exposure warning if 400 is not fast enough?
     
  13. compuwar macrumors 601

    compuwar

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    #13
    With negative film, the effect of increasing ISO decreased exposure, leading to less chance of blown out spots leaving you with the best tonal range of the film (at the cost of increased visibility of the grain.) Outside of that, ISO was really more a function of development time, and increased time led to worse resolution and more contrast (which would tend to cancel out some graduations.) Outside of not blowing the most-exposed portions of the image out I'm not aware of any benefit to shooting a particular stock at a higher ISO, can you elaborate?

    With color positive film (slides) increasing ISO did more to increase saturation than anything- I'm not sure of the effect on DR (I generally shot RVP at EI 80 for the saturation and RDPIII at 160 for the shutter speeds.) You generally weren't shooting positives for the DR anyway! Really only those of us doing our own development could "afford" to push every roll one stop though as most labs charged $3-5/roll for a one stop push.

    With digital, increasing ISO simply means amplifying the signal off the sensor- so all you're going to do is degrade the image. Sensel size has probably the most effect on dynamic range in the digital world.

    Paul
     
  14. snberk103 macrumors 603

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    #14
    Ooops - should have been more detailed in my post. Yes, I am speaking of negative film.... good point.... specifically colour.

    I was not referring to pushing or pulling a particular ISO film - but the characteristics of buying 100 ISO vs 800 ISO (from the same film family - eg. Kodak Royal).

    If one shot the same scene with the 100 ISO and the 800 ISO, being careful to maintain good exposure for each, the 100 ISO shot would appear more contrasty than the 800. If you shot a scene that had sufficient contrast that the highlights and shadows were at the limit of the 800 film to capture, then the 100 film would lose detail in either the highlights or the shadows (or both) since it didn't have the capacity to capture as much tonal range.

    I think the differences were in the 1 to 1.5 stop range i.e. if 100 ISO film could capture 6 stops of contrast, then 800 ISO could capture at most 7.5 stops....

    Oh boy, all of this goes way back though..... so memories could be fading.... :D

    Anyway, I am obviously addressing a fellow film shooter - (ex or current?) so I doubt that any of this is news.... but perhaps others reading this may learn something, eh?
     
  15. AlaskaMoose macrumors 65816

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    #15
    You will be in trouble only if you start worrying about ISO, shutter speed, and aperture. For the time being, use the instruction on the manual, or at least the one you posted:
    All depends on how fast your lens is, or if you are using flash. With your 100-400:

    ISO 100 when sunny, and "maybe" 200 if sunny but taking a photo in the shade. In fact, you may even have to go up to 400 ISO to maintain a shutter speed high enough to prevent blurred images. When you look though the viewfinder, notice the shutter speed. If it's approaching a shutter speed of 100 and you are taking pictures of birds or any moving subject, you will have to open the lens to maximum (f/5.6), and also increase the ISO to bring the shutter speed at or higher than 100 for a stationary subject. For a bird in flight, you may want to use a shutter speed of 400 and higher.

    On a cloudy day, you can try 400 ISO first, and then 800 if it needs to be higher (again, if the subject is moving you want high shutter speeds).

    Like others have said, don't be afraid experiment with your camera. But for the time being, use the options you mentioned. The key is to crank the ISO up, just as much as needed to avoid blurry subjects, and you should be able to tell when you are looking though the viewfinder (notice the shutter speed).

    I would also advise to buy one of the David Bush books specifically written for your T2i. It will save you a lot of time learning how to use it.
     
  16. Doylem macrumors 68040

    Doylem

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    #16
    I converted from film to digital. In the 'good old days' you basically set an ISO value for an entire film (typically 24 or 36 exposures). You either used the ISO value printed on the box of film, or chose a higher ISO value and 'pushed' the development times accordingly. Later film cameras would 'read' the ISO automatically, from a kind of 'bar code' pattern printed on the film casette.

    The main change with digital is the ability to change ISO values shot-by-shot... which means that ISO now joins apertures and shutter speeds in a trio of exposure variables. As a landscape photographer, using a tripod, I stick almost exclusively to the lowest ISO value - 100 - which produces optimum definition, detail and 'information' in each shot.

    As others have said, it's best to stick with the lowest ISO that's compatible with getting the shots you want. Which means reading up on the subject, some experimentation, and 'trial and error'. The relationship between aperture, shutter speeds and ISO are quite subtle. Understanding what's going on can help turn OK shots into something a bit special...
     
  17. kuaiyouming, Jul 12, 2010
    Last edited: Mar 24, 2013
  18. compuwar macrumors 601

    compuwar

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    #18
    Ex, and definitely happy to not be dealing with toxic chemicals- I'd rather futz around for an extra hour in Raw Photo Processor (best raw converter ever!) than have to deal with another crushed box of PMK again.

    Since we're waxing about the good old days...

    It is interesting to note that most serious film shooters rated most films at an Exposure Index (EI) that was lower in value than the "rated" ISO set by the manufacturer. For instance, RVP (Velvia) was rated by Fuji as an ISO 50 film, however a good many of us shot it at EI 40 (hence I generally shot it at EI 80, a one stop push- rather than EI 100.)

    This is because the ISO standard is generally geared more towards repeatability than shooting conditions. Kodak has a really good document here:

    http://www.kodak.com/global/en/professional/support/techPubs/cis185/cis185.pdf

    Note too that with B&W film, developer choice made a huge difference in the range and sharpness available as well as the optimal speed for a particular film.

    Paul
     
  19. Edge100 macrumors 68000

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    #19
    I could not disagree more.

    Modern DSLRs are very, very clean up to at least ISO1600, especially when compared with ISO1600 film. Maybe I'm in the minority, but I don't find noise objectionable at all, especially luminance noise. I regularly use my 6-year old 1DmkII at ISO3200 without too much consternation.

    I will regularly shoot above ISO100, even in full sunshine, if it allows me to get high shutter speeds. To me, sharpness is one of the most important elements of a good photograph, and if I have the choice to shoot a portrait at ISO100, f/4, 1/80 or ISO400, f/4, 1/320 with an 85mm lens, I'll take the latter every time, because I KNOW the faster shutter speed will eliminate any camera shake.

    If it's REALLY objectionable, noise can be dealt with in post, but how am I supposed to eliminate subject or camera blur in post???

    I say, don't worry about noise; use the lowest ISO you can that allows you to get the shutter speed you need.

    EDIT: one other reason one might choose to use a higher ISO is that it increases the efficiency of your flash guns, allowing you to use lower power (for faster recycle times) or to place the flash gun further from the subject (if the situation necessitates it).
     
  20. toxic macrumors 68000

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    #20
    noise ("grain," though that only really applies to film) is not a big deal. most people only post their images on the web at what, 800 pixels, tops. that's a 3" print at best. and if you use Facebook or similar, they're highly compressed anyway. I'm more worried about Jpeg artifacting than noise in that case.

    if you actually do print, then you'd know that most noise doesn't appear anyway. the only time noise is a problem is when looking at 100% crops on a computer screen.


    use the highest ISO you need to get the f-stop/shutter speed range you want.
     
  21. Doylem macrumors 68040

    Doylem

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    #21
    The direct relationship between ISO, aperture and shutter speed offers the kind of choice, trade-off or compromise that others have mentioned. It's a personal decision whether to go for a high shutter speed, for example, or minimise noise with low ISO. The 'grain' associated with fast films (or push-processed films) was more attractive - to my eyes at least - than digital noise.
     
  22. Edge100 macrumors 68000

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    #22
    I agree when you're talking about chroma noise; nothing says "digital" like random specks of colour strewn about your image. But luminance noise looks quite "film-like" to my eye.

    I agree 100% that it's a personal choice; for my work (events, PJ, and portraits), sharpness is the most important thing, and if that means going to ISO3200 to get the shutter speed I need, then so be it. For a landscape shooter, ISO speed is a non-issue because they'll be using a tripod 99 times out of 100.

    The noise reduction algorithms in LR3 are so good that even ISO3200 on my 1D2 don't really worry me anymore. Sure, I'll still go as low as I can, but noise is generally the least of my concerns.
     
  23. ManhattanPrjct macrumors 6502

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    #23
    With the advent/refinement of VR/VC, I find I tend to boost ISO less and less handheld. My auto-ISO caps out at 800 (my decision), and if I look back, I find it rarely gets there.
     
  24. kuaiyouming, Jul 13, 2010
    Last edited: Mar 24, 2013
  25. kuaiyouming, Jul 13, 2010
    Last edited: Mar 24, 2013

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