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Thread: Long exposure modes

  1. #1
    Alis's Avatar
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    Long exposure modes

    Here is a question:

    what is the difference between using the BULB mode and simply increasing the exposure time. I mean theoretically, if you could increase the exposure time with no limit, would the resulting picture be exactly the same as what we get now with BULB mode?

    It there something special the camera does on the image (noise reduction etc.) when the exposure goes about a certain limit? Is that why there is a dedicated mode in some cameras for very long exposures? Or the BULB mode is just a matter of convinience?

    Thanks!

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    Re: Long exposure modes

    Hi Ali,

    Short answer is "it's the only way you can take an exposure longer than 30 seconds"

    Other than that, nothing special. I use it all the time with my Canon TC80-N3

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    Re: Long exposure modes

    Quote Originally Posted by Colin Southern View Post
    Hi Ali,

    Short answer is "it's the only way you can take an exposure longer than 30 seconds)

    Other than that, nothing special. I use it all the time with my Canon TC80-N3
    Thanks, Colin. Hmmmm. This is very strange because in some cameras, as you know well, this bulb function is in the setting menu. So you have to go into the setting and set it on BULB mode. This does not make any sense, since they could just make the camera so that it can accept longer than 30 sec exposure times.

    I mean having it there is not even convenient...

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    Re: Long exposure modes

    Quote Originally Posted by Alis View Post
    Thanks, Colin. Hmmmm. This is very strange because in some cameras, as you know well, this bulb function is in the setting menu. So you have to go into the setting and set it on BULB mode. This does not make any sense, since they could just make the camera so that it can accept longer than 30 sec exposure times.

    I mean having it there is not even convenient...
    I think they do it on purpose so you will have too buy a remote release

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    Moderator Dave Humphries's Avatar
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    Re: Long exposure modes

    I think there's a more practical engineering reason;
    - the camera is basically a computer with an internal 'clock' or time piece counting at several MHz, i.e. several million clock pulses per second
    - you may have noticed that unlike watches, PCs keep bad time unless referenced on the internet to an atomic clock standard somewhere
    - this fast clock is mathematically divided down to give you long exposure times
    - divide down something with a .00001% error by say, 10000000 to get a long time delay and hey presto, a small timing error is now huge, enough to have people running back to the shop saying "Oi, the 10 minute exposure was only 6 minutes and it has underexposed my picture" (or similar)
    - cheaper cameras will likely have less accurate timing circuits, especially noticeable if subjected to varying temperature ranges

    So they leave it for your Rolex
    And so you have to buy a remote release

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    Re: Long exposure modes

    Quote Originally Posted by Alis View Post
    Thanks, Colin. Hmmmm. This is very strange because in some cameras, as you know well, this bulb function is in the setting menu. So you have to go into the setting and set it on BULB mode. This does not make any sense, since they could just make the camera so that it can accept longer than 30 sec exposure times.

    I mean having it there is not even convenient...
    Possibly they stick it in the meun because most people don't use it very often (if at all) and if it's the type of camera that has a function selector wheel top/left then it doesn't warrent tying up the extra space when they could fill it up with more sports/ night / Av / Auto modes etc? On my 1Ds3 mode selection is done electronically, and it's just another mode that you can cycle through.

    Probably the reason that they don't have shutterspeeds longer than 30 seconds is that it would be a "crippled mode" that wouldn't work automatically in many situations because the light levels involved would be too low for the metering to calculate correctly.

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    Re: Long exposure modes

    Quote Originally Posted by Dave Humphries View Post
    I think there's a more practical engineering reason
    Good theory Dave, but any reference clock error also divides down by the same amount so (for example) if the base clock @ say 100MHz is 1% fast then a 1 second reference pulse will also only be out by 1%

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    Moderator Dave Humphries's Avatar
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    Re: Long exposure modes

    It is April first isn't it?

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    Re: Long exposure modes

    The 30 sec timer on cameras appear to be accurate. So I don't see why they can't make accurate timers that are longer than 30sec. Besides, computers are pretty accurate in keeping time even when not connected to the internet. This means that computers have some sort of time keeping device by having a mini digital watch on the motherboard.

    I am pretty sure that cameras can be installed with mini digital watches as well. They are cheap so it won't increase cost of manufacturing signficantly.

    What are your views?

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    Re: Long exposure modes

    Quote Originally Posted by Blazing fire View Post
    The 30 sec timer on cameras appear to be accurate. So I don't see why they can't make accurate timers that are longer than 30sec. Besides, computers are pretty accurate in keeping time even when not connected to the internet. This means that computers have some sort of time keeping device by having a mini digital watch on the motherboard.

    I am pretty sure that cameras can be installed with mini digital watches as well. They are cheap so it won't increase cost of manufacturing signficantly.

    What are your views?
    I agree that Dave is sort of exagerating the time keeping problem to take advantage of it for his theory. I think he came up with the theory before it's components and had to make stuff up (I am very emotional today!)

    About Kevin's theory, I am not sure if that is actually what they had in mind but makes a lot of sense!

    But about accurate metering that Colin talks about, this could be (and I think is) only on manual mode, so I am not sure what metering he is referring to. By the way, on 5D MKII, it is on the wheel on top of the camera.

    May be I should call my good friend Chuck Westfall to end this controversy...

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    Moderator Dave Humphries's Avatar
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    Re: Long exposure modes

    Yuh, I totally fink, like Dave woz on anuver planet this moaning, mustuv got outa the rong side of bed (he's also very emoticonal)

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    Moderator Dave Humphries's Avatar
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    Re: Long exposure modes

    Of course, if this goes on, I shall just delete the posts and pretend it never happened

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    Re: Long exposure modes

    Quote Originally Posted by Dave Humphries View Post
    Of course, if this goes on, I shall just delete the posts and pretend it never happened

    hahahahahhahahahahahahahahahhahahahahhaa

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    Re: Long exposure modes

    Quote Originally Posted by Alis View Post
    But about accurate metering that Colin talks about, this could be (and I think is) only on manual mode, so I am not sure what metering he is referring to. .
    Metering works in all modes (in an advisery capacity), but it's only tied in to controlling an actual exposure in Tv & Av mode (excluding Auto, P, and other preset scene modes) ...

    ... so ... if you have a dark scene that takes the camera down to 30 seconds the metering will still expose the scene correctly - but - if you have a scene that's much darker (say one that may require a 2 or 4 minute exposure) the camera won't do it in Av mode (and if your in manual mode the metering will be off the bottom of the scale) ... it's my guess that Canon have locked out modes requiring the camera to automatically or semi-automatically expose the scene for greater than 30 seconds because there just isn't enough light reaching the metering sensors for it to work out exactly what's required and people - not understanding this limitation - would thus form a lynch mob and blast all over the internet that "Canon metering is #$%^ becuase it always gets it hopelessly wrong for exposures over 30 seconds".

    Keeping in mind that for 30 sec + exposures at log ISOs it pretty hard for the human eye to see any detail either!

    But I do see where your coming from - personally, I'd love to have exposures of >30 seconds in manual mode - would make like easier
    Last edited by Colin Southern; 4th September 2009 at 01:15 AM.

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    Re: Long exposure modes

    Quote Originally Posted by Colin Southern View Post
    Metering works in all modes (in an advisery capacity), but it's only tied in to controlling an actual exposure in Tv & Av mode (excluding Auto, P, and other preset scene modes) ...

    ...

    But I do see where your coming from - personally, I'd love to have exposures of >30 seconds in manual mode - would make like easier
    Thanks, Colin. I see what you mean now. Sounds reasonable.

    Believe it or not, I use this mode a lot, handheld: I am walking in the street with the camera hanging from the strap on my shoulder and as it rubs my back, the dial moves from Manual or Av to Bulb and usually after I take the first picture, I realize it has moved

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    Re: Long exposure modes

    Quote Originally Posted by Alis View Post
    Believe it or not, I use this mode a lot, handheld: I am walking in the street with the camera hanging from the strap on my shoulder and as it rubs my back, the dial moves from Manual or Av to Bulb and usually after I take the first picture, I realize it has moved
    Ahhh - that explains the motion blur in some of your shots!

    You'll just have to upgrade to a 1Ds3 so you won't have that problem (in fact, you can even lock-out modes that you never use)

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    Re: Long exposure modes

    Quote Originally Posted by Colin Southern View Post
    Ahhh - that explains the motion blur in some of your shots!

    You'll just have to upgrade to a 1Ds3 so you won't have that problem (in fact, you can even lock-out modes that you never use)
    I have a lot of ambitions but one thing I am sure I will never do is to move higher to 1D.

    The 5D MKII is really the best you can get for the money in my opinion. And I am saying this not because I have tried a 1D, but just because I think it has everything someone like me can wish for, including a full frame sensor at half price. 1D is good but too expensive for someone like me who does not know most of the basic stuff about photography. I mean I just can't justify the price.

    And if ever decide to go up, I will defintely buy 1Ds MK IV which is already overdue!
    Last edited by Alis; 4th September 2009 at 01:14 PM.

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    Re: Long exposure modes

    Quote Originally Posted by Alis View Post
    I have a lot of ambitions but one thing I am sure I will never do is to move higher to 1D.

    The 5D MKII is really the best you can get for the money in my opinion. And I am saying this because I have tried a 1D, but just because I think it has everything someone like me can wish for, including a full frame sensor at half price. 1D is good but too expensive for someone like me who does not know most of the basic stuff about photography. I mean I just can't justify the price.

    And if ever decide to go up, I will defintely buy 1Ds MK IV which is already overdue!
    I like to think of it as being like "learning to drive in a Ferrari" - not recommended for everyone, but nothing inherantly wrong with doing that way either; from my perspective I just enjoy having all the firmware options to "wring the most out of" - and other features add icing onto the cake. And, as you say, "not cheap" (if you want a really good return on your investment, for goodness sakes don't buy a digital camera!).

    Should be interesting to see what the 1Ds4 brings ... higher DR even at the expense of resolution would be great, but something tells me that the marketing boys will win out and we'll get something like 30MP with minimal increase in DR, and all the other bells and whistles like 2-axis "spirit level" that we've just seen in the 7D (I might add that I suggested something not too dissimilar to Canon a couple of years ago!) (feeding leveling info back to the PP packages via exif data so that shots could be (optionally) automatically leveled and cropped). Still waiting on the other dozen or so suggestions to be taken up though!

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    Re: Long exposure modes

    Quote Originally Posted by Colin Southern View Post

    ...but something tells me that the marketing boys will win out and we'll get something like 30MP with minimal increase in DR...
    Good points; I think, if I regularly come to this forum and learn enought to justify buying a camera at the price of a car (I mean second hand, sort of ) then I may very well do it.

    About the marketing boys, a few days ago, I was reading about the new G11 and the point was that although they could easily pack ~ 21 MPs on the sensor (gave 5D MKII as an example), they did not do that and that the writer thought is a good indication that Canon gave up in the race of megapixels and that it is possible that other Camera makers follow them. Until others follow Canon, he was saying that their marketing people need to educate the non-pro buyers that more pixels does not necessarily mean better image quality and that might be the start of a new era in improving factors other than the pixel number in the digital camera sensors.

    Anyway, I newer got my head around the fact that these people can put so many million pixels on a tiny surface!

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