Camera Zoom for Space photos

[ed2288]

If I wanted to buy a camera to take pictures (without a telescope) of say, saturn's rings or jupiter and its moons, what kind of optical zoom would be required. 10x, 20x, 100x? I literally have no idea when it comes to things like this. (I've noticed when you get to high end zooms, they describe them in terms of mm and f numbers, can anyone explain whats going on?) Thanks

[Buenchico]

(2-part post):

As Eddie51 states, you can't just use a camera on its own; you need a telescope.

However, the following might help you understand some of the numbers used when referring to camera lenses:

The 'focal length' of a lens determines the size of the image recorded. Because film cameras focus the light on a relatively large area of film (compared with the small size of a sensor in a digital camera), the 'true' focal lengths required for similar image sizes are different between the two types of camera. Fortunately, lens manufacturers have simplified things by referring to 'equivalent' focal lengths, which means that the size of the image in the viewfinder of either a film or digital camera is the same when an 'equivalent' length is used.

As a reference point, a cheap 'point and shoot' camera will have something like a 50mm lens. If the camera has a slight 'wide angle ' facility, the focal length might be around 30mm. If the focal length gets down to below 20mm, then we're talking about 'fisheye' lenses, rather than just wide angle' ones. Going the other way, cheaper cameras which offer a small' zoom' facility might offer a focal length of around 80 to 100mm. A more expensive camera (but still within the range of amateur photographers) might offer a 300mm lens.

[Buenchico]

The 'zoom' figure doesn't define the focal length of a lens. It only compares the 'shortest' and 'longest' lengths. For example, one camera might allow you to move the focal length between 30mm and 90mm. (That would be good for wide angle shots but not much good for long distances). Another might allow you to move the focal length between 50mm and 150mm. (That would be better for long distances but wouldn't offer a wide angle facility). Both lenses offer '3x zoom' (because the longest focal length is 3 times the shortest length) but they don't do the same job.

In practice, using a lens with a focal length much above 300mm almost always requires using a tripod to avoid camera shake. The type of lens required for astronomy requires a focal length running into many thousands of mm, which means that extra stabilization is required.

The 'f-number' of a lens refers to its size or, effectively, it's ability to capture light. (It's an inverse system, so the lower the number the better it is at capturing light). Even the best lenses (costing tens of thousands of pounds) can only capture a certain amount of light so, for astronomical photography, it's necessary to keep the camera shutter open for long periods in order to capture sufficient light to produce an acceptable image. That means that, as well as avoiding vibration, it's often necessary to use computerised equipment to compensate for the rotation of the earth.

Chris

[Teddio]

A standard 35mm film camera (35mm X 24mm negative size) often comes with a standard lens of 50mm focal length. This gives a magnification of X1, the same as the human eye. A 200mm focal length telephoto lens gives an angular magnification of X4 so objects appear four times closer.
To see the cloud belts of Jupiter or the rings of Saturn you need a high magnification of around X100. At this high magnification a sturdy camera mount is essential as slight camera movements are magnified also. You can buy long focal length telephoto lenses for cameras but they are very expensive. The best option is to buy a telescope with a sturdy equatorial mount. Adapters can be used to fit the camera to the telescope. Using a digital camera, telescope and image capture software it is possible to take spectacular photographs of celestial objects.