What's the F number on my Canon 1000 (F4.0/F29)?

[Arcturian]

What does this F number define / what result does altering it have?

Also my T ring appears to allow a setup that goes; Telescope > Lens  > T-Ring / Camera

Lens being the surprising part, will the camera take a crisp image of the light through an eyepiece AND a 10mm lens? I was under the impression you could only have Telescope > T ring > Camera

Welcoming any other beginners info

Look forward to hearing back from you guys, thanks

[Leveye]

I highly suggest either studying a book or taking a basic course in photography before jumping into astrophotography work. Simple case of cart before the horse.

[davefrance]

The f number relates to the lens aperture not the camera itself. The smaller the f number the greater the size of the aperture, the more light it lets in, but depth of field is reduced. The higher the f number the smaller the aperture, less light reaches the sensor but the depth of field is increased. Not sure what lens you have but I would assume that f4 is the largest and f29 the smallest aperture for that particular lens.  

For example in low light conditions you may choose a small f number to grab asmuch light as possible. You may find you have difficulty in getting everything in focus if the distance between foreground and background is large. A larger f number may resolve the focus issues but require the use a tripod. You may also use a small f number to deliberately throw the background out of focus to concentrate the attention t the subject.

In bright light conditions it will be necessary to user alarger f number to avoid over exposure.

Photographers (or the automatic setting on cameras) try to balance f number with speed to obtain the right light/depth of field combination for the picture being taken.

Each doubling of light is classed as one f-stop

This may help your understanding http://www.digitalcameraworld.com/2012/03/17/free-f-stop-chart-master-your-aperture/ 

Sorry no idea on the telescope/lens/t adaptor/camera option.

[ronin]

F number is a function of the lens, the f number defines the brightness of the final image, either at your eye or on a camera sensor, As far as a camera is concerned 2 lens operating at the same f number will/should mean the image brightness is the same and so the same exposure setting will result in the same picture.

An f/4 50mm lens will/can use the same settings for exposure and ISO as a 200mm lens at f/4. It was something that when you used a film camera you were generally more aware of.

An f number is easy to determine in a simple lens such as a telescope but in a multiple lens as on many cameras it is more complex and can end up being as much a definition of the light transmitted through the optics as much as lens diameter and focal length.

Consider 2 almost identical "lens" each of 4 elements same glass, same focal lengths, same seperation, On of these multiple lens is uncoated so loses 4% light at each air/glass interface, the other is well coated and loses 1% at each interface.

On the first uncoated one of the light entering only 72% makes it through, on the second coated one 92% makes it through. So f/4 on one is a lot dimmer then f/4 on the other.

[davefrance]

http://electronics.howstuffworks.com/cameras-photography/tips/aperture1.htm

[lensman57]

What does this F number define / what result does altering it have?

Also my T ring appears to allow a setup that goes; Telescope > Lens  > T-Ring / Camera

Lens being the surprising part, will the camera take a crisp image of the light through an eyepiece AND a 10mm lens? I was under the impression you could only have Telescope > T ring > Camera

Welcoming any other beginners info

Look forward to hearing back from you guys, thanks

You have some very good explanations in the previous posts, I would also advise you to do a bit of reading on the basics of optics as a foundation before getting into AP. This is by no means an easy Hobby but it is highly rewarding.

A.G

[wxsatuser]

The F number for a lens only relates to objects at an infinite distance away.

In normal photography this is usually ignored but can have an effect when the object is a lot closer.

[lensman57]

The F number for a lens only relates to objects at an infinite distance away.

In normal photography this is usually ignored but can have an effect when the object is a lot closer.

Very true, I used to do a lot of fine art photography in my younger days and quite often it involved very close distance photography using  " Macro " focusing lenses, as the distance of the  object to lens got closer the exposure had to be compensated for using the inverse- square law so yes the effective F number had changed and the lens had got " slower ".

Regarsds,

A.G