advise regarding astrophotography

[jeelan (Jeelan)]

hey guys,

I'm not into Astrophotography but wanted some feedback on something i've been curious about..

Most of the images seem to be taken by either using a dedicated astro photography camera or SLR in "prime" mode and attaching to the scope.

in each instance there is no eyepiece in between i.e. the camera attaches directly to the OTA of the telescope.

How then does one get the "magnification" required to view DSO's?

is it through significant cropping?

Always wondered about this one so if someone can enlighten me that would be great.

cheers
Jeelan

[Atmos (Colin)]

It is all to do with the focal length, whether it be a telescope or a telescope.

[LightningNZ (Cam)]

Many deep sky objects have a large apparent size.

[Southernastro (Andrew)]

Yep, the base magnification is down to the focal length of the scope, while the field of view is determined by the combination of the focal length and sensor size (full frame vs APS-C vs ccd sensor etc). Cropping the frame gives the appearance of magnifying but doesn't in reality as the pixel scale (arc sec per pixel) is not effected by cropping, only how the resulting frames are displayed on screen when "fitting to screen" - if displayed at 100% then the object of interest will be at the same magnification.

[sil (Steve)]

Just to add a bit more information for anyone else interested in astrophotography. People are used to a camera being something you point at something press a button and get a picture you can post to facebook or whatever. Astrophotos you see are rarely that simple even if using a DSLR. You take photos as you'd expect but you usually take a lot of them then align and stack them into a single image. This reduces noise from having to take longer exposures and gives you more photon data to show faint objects in better detail. Its a bit more work than just "press the button".

You also don't need a telescope to do astrophotopraphy. After all a telescope and a camera lens are essentially the same (a series of optical elements designed to capture photons entering the front and focusing them down to a region where a sensor or your eye is waiting to receive them. The differences between them effect the potential quality of the image you get: A longer optical path (focal length) gives you a greater magnification, a wider optical path (aperture; tube entrance) gives you a larger capture area (bigger light bucket) to help you capture fainter objects easier. If you want to get into astrophotography you can do it with whatever cameras you have already, you just will be limited to the constraints of the aperture and zoom and how good the camera sensor is. A tripod is essential, a tracking mount and tripod desirable, there are options.

[speach (Simon)]

The telescope is acting as a very long lens e.g. 1000mm or above so there's plenty of magnification