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Imaging the Moon

Imaging the Moon

Can I use an ordinary camera + zoom lens to image the Moon ?

Yes, but it's not easy. To get a 'decent' number of pixels you need a zoom lens of at least 500mm. Anyone who has tried pointing a camera with a zoom lens at the moon knows how difficult it is to take a decent moon photo. The bright moon in a dark sky defeats all automatic exposure metering systems (you have to use Manual exposure mode and choose your own settings) and often defeats auto-focusing systems

Photographing the Moon with a 'normal' zoom lens is a good way to start in astrophotography, since you can some practice using the camera in basic manual modes (focusing, exposure control) without being distracted by all the problems with a telescope (such as focusing, NCP alignment & 'tracking' errors, mirror 'cool down' times & 'dew shields' etc. etc.)

Atmospheric distortion makes it very hard to get 'all of the Moon' in focus at once. You thus need to take multiple shots and use 'stacking' software to select the best bits of each.

Fortunately some very good free 'auto-stacking' software exists = the best of these is Registax 6 (download v6.1.0.0 plus the update). Registax will use up to 2000 'alignpoints' to 'match up' areas of successive images for stacking. This allows it to 'chop' an image into 2000 parts and 'drop out' those parts that are too 'out of focus' (distorted) be to be any use whilst using the best of each image to produce the final stacked (and thus noise reduced) result

What camera settings should I use ?

Most Camera / Lens Image Stabilisation (IS) systems only seem to make the image worse, so turn it 'off'. Assuming you are going to 'hand hold' your camera, to avoid camera shake, your shutter speed needs to be greater than the focal length of the lens (I suggest double - so with a 500mm lens, use shutter speeds of 1/1000 or faster).

Your ISO should be set at the maximum for acceptable 'noise', typically 1 binary step down from the maximum supported (so, for a camera capable of ISO 3200, set it to ISO 1600), and then set the minimum possible aperture to get the required exposure

For a full Moon, set manual focus & then, with a 500mm lens, 1/1000 Sec, ISO 1600 you will need to set the aperture to about F11. Bracket your exposures (F8 - F16) to discover the 'best' setting and then take a dozen or more shots. If your camera can generate AVI's use the 'movie' setting instead.

The Moon is essentially 'grey' - so take 'RAW' images and convert to B&W on your PC. If your camera won't output 'RAW', choose the 'lowest' JPEG compression setting it has - and if it has a 'B&W conversion' setting (which will convert from 'RAW' within the camera), choose it, as this is likely to give more detailed / sharper results than a full colour JPEG.

The only time the Moon has any real 'colour' is during a lunar eclipse (when it 'glows orange' in Earth light).

TIP = if you have a Polarising Filter for your zoom lens, try it - it will often give improved contrast results

Do I need a guided mount ?

No, the Moon is so bright that exposure times will be short enough to allow the use of a totally unguided telescope. Indeed the Moon is the one 'target' that Dobson telescope owner can be sure to successfully image (if they can get the camera to successfully focus, that is)

In theory, the Dobson user can also image the planets, however in practice the high magnifications needed will mean that the target planet 'flies across the field of view' too fast for 'manual' tracking (unless, perhaps, you have a 'flip mirror' and are capable of the very tiny movements necessary)

What are the main problems when using a telescope to image the moon ?

1) When you point your telescope / camera combination at the moon you will typically discover you can't get it all in your field of view at the same time. It will also be very bright (especially toward a full moon) and will 'ruin' your night vision.

This means you will have to use a DSLR (the Web-Cams sensor will be hopelessly too small). Even if you use a DSLR plus Focal Reducer, you may have to image the moon 'part at a time'. Don't forget to overlap your parts by about 30%

Remember - you are going to want dozens of shots of each 'segment', which you will then 'stack' together (to get a minimal distorted result) before using 'mosaic' stitching software (such as Hugin) to produce the final image

2) Shadows cast by the Sun change quite rapidly during the moons monthly cycle. This means that images taken on different nights may not 'stitch' together without 'showing the join'

Tip - make sure your camera adapter is threaded for filters and try a green filer and/or 'variable polarising' filter (use the filter at various settings with a normal eyepiece first to discover what gives the best contrast).

For my tips on using your camera, click 'Next >>' (left, in the Navigation bar)

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