The "bulb" feature.

Discussion in 'Photography Beginners' Forum' started by Weaving Wax, Nov 14, 2006.

  1. Weaving Wax

    Weaving Wax TPF Noob!

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    I'm fascinated by long exposures. Created with the "bulb" feature on most modern SLR's. I started experimenting with it and am getting the hang of the camera through trial and error and study.. Since the shutter is opened as long as you have the button pressed what do you do about aperture? How do you use it for something like the "bulb" or does it really matter?

    Also some quick questions...

    Is depth of field simply how sharp point A to point B are in the shot?

    And the aperture is the amount of light that reaches the film?

    I'm still trying to get the hang of shutter speed and aperture and how they work together...is there any easy way to understand this? And in fully manual mode, you can set both manually, but I do know that they go hand in hand to create exposure...is there some kind-of formula that you would od in fully manual mode to get proper exposure? I might just experiment to see what works and what doesn't... Thanks!
     
  2. Big Mike

    Big Mike I am Big, I am Mike Staff Member Supporting Member

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    Aperture does have an effect when using long exposures...The aperture is the size of the hole though which the light comes. Every F stop is a factor of 2. One F stop bigger is twice as much light...one less is half as much light. So an exposure of 30 seconds at F5.6...should be the same as an exposure of 1 minute at F8 (one stop difference). However...funny things start to happen with long exposures. With film...we called it reciprocity failure...I'm not sure what goes on with digital.

    Also, Aperture controls the DOF.

    DOF can be more complicated....it has to do with what is in 'reasonable focus'...and that is kind of a subjective term. Google 'circle of confusion'. Basically, you are on the right track...the DOF is the part of the scene that is in focus...from point A to point B...those points being measured as distances from the camera's focal plane. So you could say that for a certain focal length at a certain aperture...your DOF is from 5' to 15' feet (away from the camera).

    Most modern SLR cameras have a built-in meter...that's how they know what settings to use when in auto or priority mode. When you use manual mode...you have to adjust both settings...but the camera still has a meter.

    With most cameras, when you look through the viewfinder...there is a scale. When in Auto...the camera will centre the 'needle' on the scale. When in manual...all you have to do...is to adjust the settings until the 'needle' in centred on the scale. Then if you want to change the exposure...you can adjust it so that the needle is to the left or right of the centre of the scale.
     
  3. hayden

    hayden TPF Noob!

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    Depth of field is how focused things are at all distances. If you have a larger depth of field and a subject close to you and let's say something further away in the background - that item in the background will be sharp. Vice versa.

    Aperture is the ring in the lens that acts like a diaphragm letting in X-amount of light for your values. The larger the number, the smaller the aperture; the smaller the number, the larger the aperture.

    That said, the larger the aperture, the lower your depth of field will be. Vice versa.

    Damn that was confusing. I hope you got that.
     
  4. Weaving Wax

    Weaving Wax TPF Noob!

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    I got it. Thanks. Your post was a big help as well Big Mike.
     
  5. Torus34

    Torus34 No longer a newbie, moving up!

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  6. Philip Weir

    Philip Weir TPF Noob!

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  7. Weaving Wax

    Weaving Wax TPF Noob!

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  8. fmw

    fmw No longer a newbie, moving up!

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    The traditional f stops are f 2, 4, 5.6, 8, 11, 16, 22, 32, 64. Each of one of these is set up to allow double the amount of light (or half the amount) as the f stop next to it. In other words going from f5.6 to f8 would cut the amount of light reaching the focal plane in half. Going from f5.6 to f4 would double it.

    The traditional shutter speeds are 1/500, 1/250, 1/125, 1/60, 1/30, 1/15 second etc. In other words, each step doubles or halves the length of time that the light determined by the f stop above can reach the focal plane.

    In modern cameras there are usually f stop and shutter speed options in between these as well. Don't let that confuse you.

    So, as an example, an aperture set at f8 and a shutter speed of 1/125 sec would produce the same exposure as f5.6 and a shutter speed of 1/250. Moving from f8 to f5.6 would double the amount of light and the shutter speed change from 1/125 to 1/250 would cut the amount of time in half.

    That's how the two relate to to one another.

    Changing shutter speed changes the way the camera relates to motion and changing the aperture or f stop changes the way it relates to focus and depth of field. While any number of combinations of aperture and shutter speed might produce the same exposure, they will not necessarily produce the same photograph.
     
  9. ironsidephoto

    ironsidephoto TPF Noob!

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    "Yeah, I know...I read that.. I know that it isn't a modern feature, but it is on all modern cameras, which was my point.."

    it's not on all modern cameras, especially low-quality digitals, but is on practically every SLR.
     
  10. Weaving Wax

    Weaving Wax TPF Noob!

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    Yes, I know that. I have a low quality digital camera, which is why I bought a SLR. Any reason why we keep picking this apart?

    Thanks for the answers. I find the link that Torus34 quite helpful. I'm taking notes from it. Thank you.
     
  11. Groupcaptainbonzo

    Groupcaptainbonzo TPF Noob!

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    DOF : a reasonable "Rule of thumb", is to focus on the subject, and From about a third in front of the subject, to about two thirds behind will be "in Focus".
    Reciprocity law says that if you increase exposure time by one stop, and reduce apperture by one stop, you will get the same exposure to the medium (Film/Censor). BUt a smaller apperture will give a greater DOF. so if you want to throw a boreing background out of focus you would use a wide apperture f1 if you're lucky or f4. If you wanted front to back sharpness then f22 or smaller (f45 in some cases) will do the job. All the time remembering that as you widen the apperture, you should reduce the time.
    With film , the chemicals reached a saturation point after a second or so . therefore reciprocity law failed to be correct, (Reciprocity law failiure). But you just banged a few seconds onto the exposure to allow for this (a bit more scientifically than that, but you get the picture). Some really weird things started to happen to the colours (Blue evening skies on Fuji Velvia were orgasmic), and this was often used to great effect by photographers.
    In my experience so far, I have not found this with digital, although it will get noisier with longer exposure times.
     

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