Exposure Method

Discussion in 'Beyond the Basics' started by Canon88, Dec 16, 2007.

  1. Canon88

    Canon88 TPF Noob!

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    Alright.

    I use a Canon Rebel Xt.

    Lets say I set my camera up on a Tripod and use a cable release. Lets say I'm using a few filters, one of of them is an ND8 circular filter, at f/22, ISO 100... I'm shooting in Manual because even at thirty-seconds the image was too underexposed.. so, my question:

    How do I know how long to leave the shutter open for?

    A minute? A half-hour? An hour? How does a photographer know?

    And lets say I had 15 minutes to figure it out before the sun went down, or some other scenario. Is there some device that tells me how long to keep my shutter open given the lighting conditions, other than the camera's built in meter (which finally hits 'bulb' as a last resort)?

    I refuse to believe its just a guess game.

    *sets up equipment
    "Lets guess 15 minutes"
    "okay that was too dark, lets guess 30 minutes"
    "that was too dark.. *45 minutes waisted* - lets try an hour"
     
  2. Josh66

    Josh66 Been spending a lot of time on here!

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    That's how I've been doing it (when you have to go into bulb), lol. If there is a better way, I'd like to know too.

    BTW, what are you shooting?
     
  3. jstuedle

    jstuedle No longer a newbie, moving up!

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    Find the reciprocity failure rate of the film. Meter the shot. Increase your exposure 8 stops to compensate for the neutral density 8 stop filter, compensate for the reciprocity failure of the film. Then bracket down 2 stops, proper exposure, and up two stops. That's how I would do it. Now, why in the he!! would you use a neutral density filter in a low light situation?
     
  4. jstuedle

    jstuedle No longer a newbie, moving up!

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    Oh, I reread your post and see you are shooting digital, forget reciprocity failure compensation. But the rest applies.

    Sorry.
     
  5. Garbz

    Garbz No longer a newbie, moving up!

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    Definitely not an hour. At 30 minutes + 30 minutes for the noise reduction to work one of two things will happen. Either your battery will run flat, or your sensor will cook itself in self generated heat, whether the camera survives this depends on the camera but the image you will get will suck.
     
  6. Josh66

    Josh66 Been spending a lot of time on here!

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    Damn, is 30 minutes (give or take) really the limit? The longest exposure I've done was maybe 2 minutes, but I thought all-night exposures were possible.
     
  7. THORHAMMER

    THORHAMMER TPF Noob!

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    get in the spot metering mode (or closest to it on your camera) and look at the exposures for different things in your picture. balance it out between the darkest areas and the brightest. that should help a lot. and if your not using any kind of flash/strobe you can get a fine meter reading out of manual mode.

    It compensates for your filter no problem.
     
  8. THORHAMMER

    THORHAMMER TPF Noob!

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    im sure you wont fry your sensor, Ive done plenty of 20-30 minute exposures with the 20D and it has no issues at all. I also hate the noise reduction in the camera, I dont use it. Maybye that helps for me....

    Most of the time I can hit whatever I want from 15 seconds to 3 minutes tops. since I shoot mostly city lights/industrial stuff, but if your into star trails you will end up doing some 30 min - 1 hr shots.

    I dont know if the XT can handle it , but Im prety sure without the NR you can do it really long with no issues,.
     
  9. Garbz

    Garbz No longer a newbie, moving up!

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    My D200 survived a 53minute exposure + 53minutes of NR, the image was a total unusable mess and the camera was almost too hot to touch the bottom. Like I said frying it depends on the camera. I know from at least one occasion where a 350D has died like that. The camera was on the repair bench when I was picking up a dead lens of mine from a local repair shop.

    I think generally play it sensible. 10-15 minutes gives you about the maximum usable image anyway without completely wreaking an image with noise on lower end DSLR or higher end noisy ones, beyond that go with film which has none of the limitations, other than reciprocity ??is that the right word?? failure. But even that is compensated by longer exposure times and colour correction.

    All night exposures are definitely not possible without special cameras. After about 5-15 minutes a purple tinge starts to bleed into the frame from the edges as a result of thermal noise. Also during this time pixels just die, and when they die they die hot leaving bright specs in the image. Thankfully they don't stay though. Again this depends on the camera. The D200 actually suffers less from this than the more expensive D2x.
     
  10. Sideburns

    Sideburns TPF Noob!

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    What're you taking a picture of? You may not need an exposure that long, or an ND filter that dark.

    What you could do is just meter the scene wide open....and see what it says there. Then you put the filter on, (add 8 stops) and then work your exposure out by adding one stop to shutter, taking one stop off aperture until you hit f22...it should be kinda close.
     
  11. RacePhoto

    RacePhoto TPF Noob!

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    I'm just mystified by the 8X ND in the dark, and can't wait for the answer. :lol:

    I have it. A photo of a slug crawling across a plate, and the plate needs to be sharp, but he wants speed motion blur, on the slug.

    Glacier at night, with motion blur. :lmao:

    Time exposure with shallow depth of field, is all I could come up with. But at f/22 that makes no sense, so I'm lost.

    What's the subject and why a time exposure at f/22 with an 8xND filter?
     

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