Astrophotography with a Budget Digital Camera

This site aims to set out my experiences of lunar and planetary astrophotography with a low cost digital camera. I'm an amateur astronomer with an interest in astrophotography. Neither my telescope, an equatorially mounted but undriven Orion Optics (UK) 150 mm F/6 Newtonian reflector, nor my fairly light polluted suburban location permit me to photograph deep sky objects. In recognition of this and attracted by the impressive images others have obtained, I have turned to photographing the Moon and planets.

Moon film camera image In recent years I have tried eyepiece projection photography through my telescope with an SLR film camera. Once I had discovered the Hartmann Mask(1) as a focusing aid, I obtained some moderately successful results.
This image is a typical example and shows part of the lunar terminator at 21:31 UT on 9 February 2003, when the Moon was 8 days 10 hours old and illuminated by 54 %. Craters Maginus, Saussure, Orontius, Deslandres, Walter, Regiomontanus, Purbach, Arzachel, Alphonsus and Ptolemaeus line the terminator. The image was obtained by eyepiece projection using a 9 mm Kellner, giving an effective focal ration of f/50. A 1/15 s exposure on to Fuji Superia Xtra 800 was used. The 7" x 5" machine print was scanned at 200 dpi and then resampled to 30 % and saved in JPEG format to produce the image shown here.

While fairly well focused, the resolution of the image is quite coarse and many of the features shown in plates 13 of the 'Hatfield Photographic Lunar Atlas' (2), for similar lunar ages, have not been resolved. My intention in digital camera astrophotography is to improve on this.


Many fine examples of digital camera astrophotography are achieved by prominent members of the digital_astro Yahoo Groups mailing list, often using high-end digital SLR cameras. This website, however, investigates what can be achieved with a low cost digital camera.
Main features of Fujifilm FinePix A405 Zoom:

No. of effective pixels: 2 million
Nos. of recorded pixels: (still) 2304 x 1728, 1600 x 1200, 1280 x 960 and 640 x 480 (movie) 320 x 240, 160 x 120
Lens: Fujinon 3X optical zoom lens
Focal ratio: f/3.0-f/7.0 (wide angle), f/4.8-f/10.8 (telephoto)
Focal length: 5.5 - 16.5 mm
Shutter: 1/2 to 1/2000 s
Sensitivity: ISO 160-200 (equiv.) when flash off
The camera I have recently acquired is a Fujifilm FinePix A405 Zoom camera. This is a basic point and shoot camera with a 3X optical zoom capability. Although a 2 megapixel camera, it uses the Fujifilm Super CCD technology to provide the option of an interpolated 4 mega pixel output. Summary technical information is shown opposite, and more detailed information is provided on the Fujifilm website.
example of vignetting

10 day Moon 2 Jan 2004 image Click on image to see full size
The camera lens cannot be removed and so there is no way of using the camera for prime focus or eyepiece projection astrophotography. Instead, the camera must be held at the telescope eyepiece, using the afocal method. This method has long been an available, if tricky, option for astrophotography with non-SLR film cameras. It is somewhat easier to apply with digital cameras because of the LCD screens mounted on the camera backs and the contrast-based automatic focusing method generally used.

The position and orientation of the camera with respect to the light cone emerging from the eyepiece is critical, otherwise vignetting - capturing an incomplete image surrounded by shadow ( see left, upper) can occur. In the example shown, obtained during first use of the camera at the telescope, the camera was used at 0.3 Mpixel resolution (640 x 480) with maximum optical zoom and held to a 9 mm Kellner used with a 2x Barlow lens. The craters Clavius, Blancanus and Scheiner can be seen in the image, which was obtained on 2 January 2004 at approximately 21:45 UT, when the Moon was 10 days old. Even in this early, vignetted image, the resolution is much nearer that in Plate 10b of the Hatfield atlas (2).

The image below was obtained during the same first session and shows a wider angle view. This was obtained with the camera set to its maximum 4 Mpixel resolution (2304 x 1728) and held near a 25 mm Plössl ocular used with the 2x Barlow. If viewed at full size, the Clavius area is almost on the same scale as in the upper image and similar resolution has been obtained. Yet, the use of higher camera resolution and a longer focal length eyepiece has enabled a much larger area of the Moon's surface to be captured in one shot. The greater eye relief (3) of the longer focal length Plössl also enabled the image to be obtained more easily with less risk of vignetting. Both these images were obtained with the camera hand-held. They have also been converted to grey scale and cropped, and the lower image has been rotated by 30 degrees.

While these initial images obtained with the digital camera already surpass - in terms of resolution - those I obtained with film camera techniques, there is much still to investigate. For example, fixing the camera position (either with a tripod or with a telescope-mounted device) should reduce the likelihood of vignetting. Also, multiple images obtained during an observing session could be digitally 'stacked' to improve resolution. Camera resolution options and other digital post-processing techniques remain to be explored. Please follow the links below to further pages describing such investigations:

The links below are for pages of gallery images obtained with the digicam:

Please direct comments on this website to: chris.c.holt@ntlworld.com

Footnotes

1. A Hartmann mask is an opaque cover for the objective end of the telescope, with two or more similar large diameter holes in it. Light received from a bright star will form a double image (or a multiple image, if more than two holes) at the eyepiece when the telescope is incorrectly focused. As the image becomes focused, the images merge, becoming fully superimposed when the telescope is focused. Further details can be found by following this link to a site by Jerry Lodriguss.

2. Cook, J., 'The Hatfield Photographic Lunar Atlas', Springer-Verlag, London, 1999.

3. 'Eye relief' is a measure of how far from an eyepiece is the plane of the exit pupil - the disc of light projected by the eyepiece when the telescope is focused on a celestial object. This is where the pupil of the user's eye should be placed and varies with eyepiece design and focal length. For Plössl eyepieces the eye relief is about three quarters of the focal length, so about 18 mm for a 25 mm Plössl.

Last updated: 4 January 2005