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Afocal imaging

Video and Webcam - CCD - Digital Cameras (compact or DSLR Photographic Film - PrimeFocus and Eyepiece Projection - Afocal Imaging - Piggyback and Camera Direct - Filter Use

Afocal imaging is in principle as simple as camera direct imaging . Place the camera with its lenses in place at the eyepiece of the telescope . This is not quite as simple as it seems . The alignment must be very accurate and vignetting (reduction of the field of view) is often very difficult to avoid . This is certainly the case if the telescope and camera are supported separately . Because tracking of the object in the sky is necessary the tlescope will be moving constantly , making it necessary to move the camera as well . I tired this way , and though I got some images from it (see the gallery lunar section) I am not planning to pursue this method further .

On the other hand , if alignment is achieved the ZOOM function of a camcorder may be used to vary the magnification of the images .

There is , of course a way of having the camera follow the telescope , namely , as Francois du Toit does it : Make a bracket . This is acceptable only if the camera is very small (light) or if the telescope is rather large (heavy) . For my camcorder , a Sony PC100 , The smallest telescope I would consider for this method would be a 20cm SCT with a medium sized German Mount . This is exactly what I have availoble (Celestron C8 and a GP-DX Mount) .

Most of the techniques described for "Camera Direct" imaging will apply for afocal imaging as well , e.g. the use of "Low Lux" or "Nightshot" facilities .

One major advantage of afocal imaging is the use of readily available equipment , such as a standard consumer type camcorder , an item which many people already own .

One disadvantage mentioned by my friend Ole Nielsen is the fact that the opticas of the video camera is not of an optimum quality for astronomical imaging . Very good results can be achieved anyway with a lot of patience and a substantial amount of time for image processing . One excellent example is Ole's afocal image of Saturn made with a 125mm SCT and a standard camcorder , plus a LARGE amount of image stacking and processing .

Trying out afocal imaging is recommended if you have the camera and telescope at hand , and cannot afford a dedicated astroimaging camera . The same technique may , of course , be used with a pair of binoculars , using the camera zoom function to increase the magnification (that is if you can fix the camera relative to the binoculars) .

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Last update 21 January 2006 by Jan Andersen.
Background image : Video image of the Pleiades
Top caption : Lunar Eclipse 21-01-2000