Basic Camera Help

[rich_8377]

I have just been asked some questions on a picture I posted and realised that I know nothing about photography or camera settings. Some help would be appreciated. These are going to be very, very basic questions to some of you so please can you reply in as basic a manner as possible. Here goes. What is an f number and what f number should my camera be set to? What ISO is the best to set the camera to? Thanks

[ronin]

F number: The ratio between the focal length and the diameter of the objective.

So if the lens has a diameter of 60mm and a focal length of 120mm the f number is f/2.

That is the basic idea.

However I believe that on a camera lens they take into account the light loss through the optical system, so if the lens measure to be 60mm it may act as if only 40mm and you will see/get a reading of f/3.

Further to reduce aberations the lens most likely has baffles that cut into the light and so reduce the effective aperture.

But in "simple" terms "focal length / diameter."

The property of the f number is that for the same f number the image produced on the film or sensor will be the same intensity, So the exposure time is the same on a 50mm lens at f/8 as on a 100mm lens at f/8 and a 500mm lens at f/8.

What alters in this case is the size of the image and the diameter of the objective lens.

On a camera if the f number is too fast f/2.8 then the image tends to be a bit soft, usually better (sharper) results at f/4 and above that. F/8 always was the sort of optimal.

ISO on digital cameras is the amount that the camera amplifies the intensity of the charge caused by the light landing on the pixels. As you amplify this you also amplify the noise. What is best, not really a clue as the answer is the lowest you can get away with. Try ISO 200 that always was a good offering in the days of film. I have seen 400, 800 and 1600 fairly often, again this depends on the amplifier of the camera and how good it is. Your camera may well have the option to take a black frame and so reduce noise when you take a shot. Mine does if the exposure is greater then 1 sec.

Finally it is digital, write down the settings you have set, hit the remote release and see what comes out. Don't press the release on the camera, causes too much shake. If it is rubbish there is a Delete button.

[VigdisVZ]

I have just been asked some questions on a picture I posted and realised that I know nothing about photography or camera settings. Some help would be appreciated. These are going to be very, very basic questions to some of you so please can you reply in as basic a manner as possible. Here goes. What is an f number and what f number should my camera be set to? What ISO is the best to set the camera to? Thanks

Detailed specification of how the F number works can be found on wikipedia. All you need to know at this stage is that a low F-number means a big light opening. And a high F-number means that the light opening is small.

In practice it means that if you set the F-low, you can take pictures with a shorter exposure time but they will look slightly different. For instance the image will only be sharp just at the focus plane ie objects too far away and too close will be fuzzier. While a high F-number means your plane of focus will be wider.

For astrophotography you basicly want the F-number as low as possible then dial it up 1 or 2 clicks, that means that the lens flares appear less bleedy and you get a slightly better quality image.

ISO is amplification. At around 1600 to 3200 the noise and grain becomes noticable. For astrophotography you can play around with the settings to see where you like how the image turns out, but generally a low ISO means you have to take longer exposures but the image will be less noisy.

Just ask away more!

[rich_8377]

Detailed specification of how the F number works can be found on wikipedia. All you need to know at this stage is that a low F-number means a big light opening. And a high F-number means that the light opening is small.

In practice it means that if you set the F-low, you can take pictures with a shorter exposure time but they will look slightly different. For instance the image will only be sharp just at the focus plane ie objects too far away and too close will be fuzzier. While a high F-number means your plane of focus will be wider.

For astrophotography you basicly want the F-number as low as possible then dial it up 1 or 2 clicks, that means that the lens flares appear less bleedy and you get a slightly better quality image.

ISO is amplification. At around 1600 to 3200 the noise and grain becomes noticable. For astrophotography you can play around with the settings to see where you like how the image turns out, but generally a low ISO means you have to take longer exposures but the image will be less noisy.

Just ask away more!

F number: The ratio between the focal length and the diameter of the objective.

So if the lens has a diameter of 60mm and a focal length of 120mm the f number is f/2.

That is the basic idea.

However I believe that on a camera lens they take into account the light loss through the optical system, so if the lens measure to be 60mm it may act as if only 40mm and you will see/get a reading of f/3.

Further to reduce aberations the lens most likely has baffles that cut into the light and so reduce the effective aperture.

But in "simple" terms "focal length / diameter."

The property of the f number is that for the same f number the image produced on the film or sensor will be the same intensity, So the exposure time is the same on a 50mm lens at f/8 as on a 100mm lens at f/8 and a 500mm lens at f/8.

What alters in this case is the size of the image and the diameter of the objective lens.

On a camera if the f number is too fast f/2.8 then the image tends to be a bit soft, usually better (sharper) results at f/4 and above that. F/8 always was the sort of optimal.

ISO on digital cameras is the amount that the camera amplifies the intensity of the charge caused by the light landing on the pixels. As you amplify this you also amplify the noise. What is best, not really a clue as the answer is the lowest you can get away with. Try ISO 200 that always was a good offering in the days of film. I have seen 400, 800 and 1600 fairly often, again this depends on the amplifier of the camera and how good it is. Your camera may well have the option to take a black frame and so reduce noise when you take a shot. Mine does if the exposure is greater then 1 sec.

Finally it is digital, write down the settings you have set, hit the remote release and see what comes out. Don't press the release on the camera, causes too much shake. If it is rubbish there is a Delete button.

Thanks for your help guys... Just what I was looking for.

[Robny]

Basically, ISO is the sensitivity of the sensor. The higher the value the more sensitive the sensor will be to light, but lower quality. The lower the value the less sensitive it is but higher quality. Generally you want to use the liwest possible.

F number - Is a value on the lens (2.8, 4, 5.6, 8, 11 and so on) the smaller the number the less that will be in focus (only what you focus on) the bigger number, the mire thst will be in focus (front and back of subject). But...it has to be balanced by the shuuter speed, the smaller the number the faster the shutter speed should be, the bigger the number the slower the shutter speed should be.

This may have raised more questions than you had originally but this is as basic as I can make it. There is a lot more involved and a lot more technical than I put it, but I hope it helped, if this is too tame I can go into a lot more detail.

Rob

Sent from my phone, please excuse and grammer and speling

[dph1nm]

Basically, ISO is the sensitivity of the sensor. The higher the value the more sensitive the sensor will be to light, but lower quality.

No - the sensitivity of the sensor to light is fixed. ISO makes no difference to this. In effect, all ISO really does is change the gain, which is similar to multiplying your images by a constant in software. And as noise and signal get multiplied by the same amount then the signal-to-noise ratio, which determines how good your image looks, remains the same. The only two issues where it particularly makes a difference for astro work are in saturation (lower ISO means more range, so less saturated stars) and read noise (which for some cameras is lower at high ISO, so for shortish exposures high ISO is best). Also at very low ISO you can end up with quantisation problems, where several photons are required to trigger one count on the camera. It is not a good idea to be in that regime!

NigelM

[Robny]

No - the sensitivity of the sensor to light is fixed. ISO makes no difference to this. In effect, all ISO really does is change the gain, which is similar to multiplying your images by a constant in software. And as noise and signal get multiplied by the same amount then the signal-to-noise ratio, which determines how good your image looks, remains the same. The only two issues where it particularly makes a difference for astro work are in saturation (lower ISO means more range, so less saturated stars) and read noise (which for some cameras is lower at high ISO, so for shortish exposures high ISO is best). Also at very low ISO you can end up with quantisation problems, where several photons are required to trigger one count on the camera. It is not a good idea to be in that regime!

NigelM

I'm sure very well and true, but OP asked for basic description of what it was, my description was basic of how/when one would chane iso give a specific scenario. Granted, my description was terrestrial photography related.

Rob

Sent from my phone, please excuse and grammer and speling

[Psychobilly]

Have you had a chance to have a look at the 101 in the photography sub-board...

http://stargazerslou...eginners-guide/

[lensman57]

Have you had a chance to have a look at the 101 in the photography sub-board...

http://stargazerslou...eginners-guide/

That is all very interesting but inaccurate in some areas. Lightmeters do not lie. It is up to the photographer to correctly interpret the reading and so on.

A.G