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Thread: Exposure time vs. ISO

  1. #1
    jmvdigital
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    Exposure time vs. ISO

    I have a theoretical question for you guys...

    Given an average ambient temperature, would an image exhibit higher IQ/less noise with a shorter exposure at higher ISO, or a longer exposure at a lower ISO? I caught this comment by Thierry in another post (about the eMotion 75 @ 800 ISO):

    It also depends on the ambient temperature when your are shooting: my guess (but it's only a guess) is, that it will give a better result with ISO 800 at 4 sec. than at ISO 100 with 30 sec.
    I have no idea if this a valid theory or not, and it probably differs greatly on the type of back. Any insight or real world experience on this?

  2. #2
    thsinar
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    Re: Exposure time vs. ISO

    I am still guessing, since not had the time to experience it: yes, I believe this is true, WHEN the temperature is "high" (30 C ++).

    Thierry

    Quote Originally Posted by jmvdigital View Post
    I have a theoretical question for you guys...

    Given an average ambient temperature, would an image exhibit higher IQ/less noise with a shorter exposure at higher ISO, or a longer exposure at a lower ISO? I caught this comment by Thierry in another post (about the eMotion 75 @ 800 ISO):



    I have no idea if this a valid theory or not, and it probably differs greatly on the type of back. Any insight or real world experience on this?

  3. #3
    Sr. Administrator Jack's Avatar
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    Re: Exposure time vs. ISO

    I don't know either, but I have 30 second exposures at ISO 50 and 100 with my P45+ that are essentially noise free.
    Jack
    home: www.getdpi.com

    "Perfection is not attainable. But if we chase perfection, we can catch excellence."

  4. #4
    thsinar
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    Re: Exposure time vs. ISO

    the temperature is the issue, Jack: it is like poison concerning the noise.

    30 seconds at 20C are not such a problem, but then, if you shoot under tropical/equatorial temperatures it will dramatically change the game. This added to long exposures, which again adds to the internal temperature of the sensor, makes life difficult.

    Thierry

    Quote Originally Posted by Jack Flesher View Post
    I don't know either, but I have 30 second exposures at ISO 50 and 100 with my P45+ that are essentially noise free.

  5. #5
    Sr. Administrator Jack's Avatar
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    Re: Exposure time vs. ISO

    Quote Originally Posted by thsinar View Post
    the temperature is the issue, Jack: it is like poison concerning the noise.
    Understood Thierry, but the OP asked his question with the qualification of "average ambient temperatures" ...

    Cheers,
    Jack
    home: www.getdpi.com

    "Perfection is not attainable. But if we chase perfection, we can catch excellence."

  6. #6
    Administrator, Instructor Guy Mancuso's Avatar
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    Re: Exposure time vs. ISO

    From someone that lives in hell out here in the sunny bake your butt Arizona i have yet to run into high temp noise issues with any length in exposures yet. But i would imagine if we let any back just sit in the sun for any length of time you may have a issue but that would be with any camera out here. i always thought about this since residing 30 years here and film I always protected but digital I just don't leave stuff in the car that can reach 140 degrees in a matter of minutes and even hotter.
    Photography is all about experimentation and without it you will never learn art.

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  7. #7
    thsinar
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    Re: Exposure time vs. ISO

    yes, understood as well, it all depends what is "average ambient": in South East Asia it's around 30C all over the year.

    cheers too,
    Thierry

    Quote Originally Posted by Jack Flesher View Post
    Understood Thierry, but the OP asked his question with the qualification of "average ambient temperatures" ...

    Cheers,

  8. #8
    thsinar
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    Re: Exposure time vs. ISO

    if you can protect your back, it's perfect, but there are situations (and I have experienced them) where you are shooting the whole day long with around 40C: no way to keep the back cool, by any means, unless you bring some ice and wrap the back (I have done it).

    Thierry

    Quote Originally Posted by Guy Mancuso View Post
    From someone that lives in hell out here in the sunny bake your butt Arizona i have yet to run into high temp noise issues with any length in exposures yet. But i would imagine if we let any back just sit in the sun for any length of time you may have a issue but that would be with any camera out here. i always thought about this since residing 30 years here and film I always protected but digital I just don't leave stuff in the car that can reach 140 degrees in a matter of minutes and even hotter.

  9. #9
    Super Duper
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    Re: Exposure time vs. ISO

    Quote Originally Posted by Guy Mancuso View Post
    From someone that lives in hell out here in the sunny bake your butt Arizona i have yet to run into high temp noise issues with any length in exposures yet. But i would imagine if we let any back just sit in the sun for any length of time you may have a issue but that would be with any camera out here. i always thought about this since residing 30 years here and film I always protected but digital I just don't leave stuff in the car that can reach 140 degrees in a matter of minutes and even hotter.

    But it's a dry heat!

    I've shot in a lot of varying climates from open the oven and stick your head in it Tucson to freeze your butt off snow up around your ankles (remember my ankles are higher up than most ) . I like keeping the ISO as low as possible and shoot about 99% of my stuff at 100 on the P30+; the big thing I'm looking forward to with the P45+ is being able to lower the ISO to 50.

    By the way, Guy is being very conservative when he says the inside of a car here can get to 140 degrees. I've haven't seen it done for awhile but figure if the sidewalk can get hot enough to fry an egg figure what the inside temperature of a vehicle is.

    As far as noise goes I haven't had much problems.....

    don
    Don Libby
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  10. #10
    Sr. Administrator Jack's Avatar
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    Re: Exposure time vs. ISO

    Quote Originally Posted by thsinar View Post
    yes, understood as well, it all depends what is "average ambient": in South East Asia it's around 30C all over the year.

    cheers too,
    Thierry
    I am sure it is, but Justin is from Colorado.

    Moreover, I've used my back in 35 C temps without any noise issues, so in addition to outside temperatures I suspect some of it depends on the design of the back.

    Cheers,
    Jack
    home: www.getdpi.com

    "Perfection is not attainable. But if we chase perfection, we can catch excellence."

  11. #11
    carbonmetrictree
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    Re: Exposure time vs. ISO

    I did notice a density of noise when in 30F weather shooting at night with the 1dsMk3. Each exposure took 3-4mins to creep into the card, but when I opened them up later, I noticed that the noise in the shadows were a bit more suppressed than at 80F. I tend to bracket when possible at night, so this wasn't too much of a concern for me.

    Off the topic- I was very shocked to see that the 1dsMk3's buffer took exponentially longer as it got colder with the same exposure times. Some shots took around 4 minutes to record to the card.



    I was around a steam boiler last night and the temperature was probably around 90F, no issues whatsoever with noise. With the plus series Phase backs, I can honestly tell you that at ISO 100 will be noise free especially because of the dark slide reference capture right after each long exposure.

  12. #12
    thsinar
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    Re: Exposure time vs. ISO

    I was not referring to or comparing any brand, Jack, just speaking about simple physical laws: that is true for any brand.

    I have shot with many brands under these conditions, even a P45+.

    Best regards,
    Thierry

    Quote Originally Posted by Jack Flesher View Post
    I am sure it is, but Justin is from Colorado.

    Moreover, I've used my back in 35 C temps without any noise issues, so in addition to outside temperatures I suspect some of it depends on the design of the back.

    Cheers,

  13. #13
    Sr. Administrator Jack's Avatar
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    Re: Exposure time vs. ISO

    Quote Originally Posted by thsinar View Post
    I was not referring to or comparing any brand, Jack, just speaking about simple physical laws: that is true for any brand.

    I have shot with many brands under these conditions, even a P45+.

    Best regards,
    Thierry
    Thierry,

    I understand the physics too and was not referring to any specific brand either --- more design in general and more specifically was simply suggesting that perhaps the different methods used to cool the sensor can also come into play.

    Cheers,
    Jack
    home: www.getdpi.com

    "Perfection is not attainable. But if we chase perfection, we can catch excellence."

  14. #14
    jmvdigital
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    Re: Exposure time vs. ISO

    So the moral of the story is to stay with the lowest ISO you can for prolonged exposures, unless you are in a super-hot tropical/desert environment, then experiment with higher ISO/shorter time exposures.

  15. #15
    Workshop Member lance_schad's Avatar
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    Re: Exposure time vs. ISO

    On our website (http://www.captureintegration.com/ph...ne-tech-specs/) we have a chart that maps out the maximum exposure time at various ambient temperatures.
    As with any camera system, the longest exposure a Phase One back can produce before prohibitive noise is produced depends on the ambient temperature of the air. Unlike other camera systems Phase One backs longest practical exposures are measure in minutes and hours rather than seconds.

    L
    LANCE SCHAD - Digital Transitions - Phase One,Mamiya | Leaf,Arca-Swiss,Cambo, Profoto
    direct/cell:610-496-5586 office:877-367-8537x224
    http://www.digitaltransitions.com email:[email protected]

  16. #16
    Sr. Administrator Jack's Avatar
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    Re: Exposure time vs. ISO

    And FTR, I'd like to highlight this little footnote on the chart Lance linked to:

    "Note 2: Our testing has shown the P45+ to produce the best long exposures."

    ... Just in case that has any impact on what you decide to buy .

    Cheers,
    Jack
    home: www.getdpi.com

    "Perfection is not attainable. But if we chase perfection, we can catch excellence."

  17. #17
    Administrator Bob's Avatar
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    Re: Exposure time vs. ISO

    A good paper that explains this phenomenon fairly well can be read here www.hiddenloft.com/notes/CCDtemp.pdf
    -bob

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