# Bulb mode -- help please



## ben.

I am fairly new to photography, i have a canon rebel xsi and i heard about bulb mode. Is it something you activate or something you buy? Might sound stupid but i heard both so far.

If it is something you activate, how?


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## ann

you just need to dial down the shutter speed control until you reach bulb. It is used for time exposure, which of course should be done on a tripod. Also , a stop watch helps to track the time


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## ben.

well mine doesnt do that, on the xsi you can go as low as 30 seconds and 1/4000 second, there is nothing past that. what am I doing wrong?


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## bigtwinky

I have an XSI and its there.

B should be the next value after the 30 second shutter.  You can probably get it in M or TV modes.  Note that without a cable or wireless trigger, you will have to physically hold down the button.  If you are doing a 2 minute exposure, thats a long time to hold the camera, and it needs to be steady to get crisp images.

There are some wireless remotes for the XSI that allow to keep the shutter open.
Should be about $25.  Check out Simon's Camera or Photoservice in the Old Montreal area, or Lozeau on St-Hubert. 
Amazon.com: Canon Wireless Remote Control RC1 for Digital Rebel: Camera & Photo


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## Actor

bigtwinky said:


> Note that without a cable or wireless trigger, you will have to physically hold down the button.


Invest in a shutter release cable.  They're designed to exert a net zero force on the shutter and are cheap.


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## ben.

i am gonna use bulb mode in the next 3-4 days probably with a tripod and a shutter release cable. i am planning on shooing the stars (so that you can see the path of them) with a shutter speed of 20-30 minutes. what do you think should my f/# be and my ISO??

i am fairly new to photography, thanks for understanding


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## Soocom1

20-30 min is ok, but keep in mind that you have surrounding light than can interfere with the shot, so pay attention to that. 
Any F stop and ISO will work, but obviously the smaller the aperture, or slower the ISO the longer the shot. You will defiantly see star tracks with that length. 
Set up also with the North Star, and create a circular star pattern.


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## ben.

thanks, so you think i should use some low f stop, thanks, what does ISO exactly do? im a newb so sorry


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## Soocom1

ISO stands for International Standards organization. It is the international body that sets standards for weights, measures, etc. (Think ISO 9000 Certified.) Same people.  In the regards to film, ISO is the speed that is rated for film or in this case digital sensor sensitivity.  Ergo: how fast the film/sensor is. Or how light sensitive it is. The smaller the number, the slower the speed. I.e. 25 speed is slower than 640. 

the faster the speed, the darker things can be, but it creates noise. This is junk information in a digital image. In film it shows up as grain size. The faster the film the grainer it is. 

Try this link: Catching the Light: Astrophotography by Jerry Lodriguss

Some good info, and great examples of what can be done. 

For really good astrophotgraphy, a Wide open aperture is good, with a med-to med slow speed. (But this depends on the image you want).


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