just a quicky

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matty198111

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mat
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just noticed on my daughters camera there is a setting that you can change from f3.1to f 6.4 just wandered what it means

is it the amount of light the camera lets in, she would like to take a picture of the stars over along period of time but not sure what setting to put it on also how long should we set it for as it goes upto 1200 seconds/20 mins

cheers
mat
 
A very basic explaination is this - the f number (ie f3.1 or f6.4) refers to the size of the hole in the lens - its aperture. Going from f3.1 to f 6.4 means the hole is being made smaller, so the shutter has to be open longer to allow more light through. The smaller the hole (ie the higher the f number is - in your case f6.4) the bigger the depth of field is. Depth of field means the amount of stuff that is in focus infront and behing the point of focus, so if you focus on a tree that is 10m away, everything from 9m to 12m will be in focus at f3.1, and using f6.4, everything from 8m to infinity will be in focus. However, the figures I am quoting are just for example, not accurate.
The relationship between the aperture (hole in the lens) and the shutter speed (time the shutter is open for) is an important one to learn, as for every f-stop you open or close the lens, you need to halve or double the shutter speed. I am sure there will be someone here who can produce a graph that will illustrate this way better than my clumsy attempts while I am burning the lunch !
Does that make any sense to you - it seems to to me, but if not to you then I will try again...!
As for the shutter opening for stars, I have no idea, but why not try a few different times to experiment - you will need a tripod or some other way to hold the camera still (a sock filled with dry beans or rice would do well) and a shutter release of some sort may also be good.
 
The 3.1 to 6.4 is the aperture, smaller number means bigger hole to let light in.
For stars over a long period, you will want a medium to big aperture and a long shutter speed. However on a camera like that, the image will probably be pretty noisy. You will need to make sure that the camera doesnt turn the ISO up to high by itself, as this will make a noisy image.
 
thats what i love about this site, ive been reading about f3.4 etc on the net and couldnt get me head round it, come on here and some one tells you in english lol

cheers mate

mat
 
Usually the lower the better until you go past the camera's normal range, Im not sure what the base ISO is of that camera. On DSLR's its usually 100 or 200. Find out what the default is and leave it there, or the next higest one.

My D700 goes down lower, but its base is 200. Thats the normal and you only go lower if you are in really bright light. Some say image quality decreases once you go below the base level, but never tried, so dont know.
 
The higher the ISO is the lower the image quality, but the less light you need for your picture.
Can you picture the grainy shots of concerts ? That is usually the result of having a high ISO setting - say from 800 upwards. However, an advertising picture of say a bottle of wine will have every possible detail, and that will be in part down to a low ISO. Megapixels will be another factor here, but lets not complicate matters too much..
Try taking a picture of the same subject. Set the camera to its lowest ISO setting for one, then to its highest for the other, make a note of the shutter speed and aperture settings for each and then look carefully at both - one will appear sharper and more detailed, the other will appear course and grainy/noisy. The high ISO picture will be the noisier one, and either a faster shutter speed will have been used, or a higher f number, or maybe both.
In practice this means that with a high ISO setting you can take pictures in lower light levels given the same settings.
 
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