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First light

The moon, seen from Leeds on 14 August 2003


First light
The moon, age 17d12h, phase 91% [Leeds UK, 14 August 2003; ETX125EC+Canon 10D]

This photograph is labelled "First light" because it's the first time we've used the Canon 10D with our telescope, a Meade ETX125EC. Attaching the camera needs a T-ring adapter, which took some time to get hold of.

The camera was at the telescope's prime focus, attached to the rear port, so the scope is just acting as a rather large telephoto lens, in this case with a focal length of 1.9 metres. There's no eyepiece involved. To reduce vibration, we used the self-timer and the mirror lock-up feature on the camera. The shots were taken from indoors, on a window shelf ... not usually recommended! The focusing wasn't perfect (that's one of the hardest parts of astrophotography), and the moon was low.

The exposure here is 1/125sec at ISO 400, short enough that guiding isn't necessary. It's very easy to overexpose the moon -- always remember that it's a sunlit surface (albeit a rather dark one), and exposures of around 1/30 to 1/125 sec will usually be OK. This explains why you don't see photographs of the moon in a starfield, other than during a lunar eclipse -- the exposure's just too short to capture stars.

If you're not sure, underexpose. This can be corrected in post-processing, but there's nothing you can do with an overexposed image.

This is a 1/3-scale montage of two shots; the moon won't quite fit in one frame when it's nearly full. Montage was done in Composition with some post-processing in Photodesk: colour balance, some sharpening (a bit too much, in fact) and a small gamma adjustment to brighten it up.

ROCchart has a very useful 'field of view' (FOV) indicator, which will show you what you can actually see through any particular optical insrument. The picture below is a screen grab of the program, showing how the FOV dialogue is set up for the combination of Canon 10D and the ETX125 telescope.


ROCchart's FOV, with (inset) the actual view

The lilac rectangle is ROCchart's FOV indicator. The Type is Box aperture -- for binoculars you might choose Circular field. The scope's focal length is 1900mm, and the chip in this particular camera is 22.7x15.1mm; for a 35mm camera you'd enter 35x24mm. The inset picture is an actual (uncropped but scaled) photo, so you can see how accurate it is. The terminator is in the right place, too. The small amount of rotation is caused by the camera not being quite level.

Image details (one of two)

Taken : 11:55:04pm Thu 14 Aug 2003
Camera : Canon EOS 10D
Size : 3072 x 2048 pixels
Filesize : 1481 Kbytes
 shooting information
Exposure : 1/125 sec at ISO400
f : ?
Focal length : 1900mm
Bias : 0
White balance : Auto
Metering : Average
Flash : Not fired
Orientation : x0,y0=left,top
Compression : 3
 canon information
Image number : 001-2078
Sequence number : 0
Quality : Fine
Image size : Large
Contrast : Normal
Saturation : Normal
Sharpness : Normal
Macro mode : 0
Self-timer duration : 2.0
Digital zoom : Off
Flash mode : Off
Flash : Not fired
Flash bias : 0
Easy-shoot mode : Manual
Focus mode : Manual
Focus type : 2
Subject distance : 0
Focus mode 2 : 65535
AF point selected : 0
AF point :  (0 focus points)
Metering mode : Centre-weighted
Exposure mode : Manual
White balance : Auto
Continuous drive mode : Single shot / timer
Image type : IMG:EOS 10D JPEG
Owner : Lee and Chris
Serial number : 259143675

© 2003 Lee Montgomerie / Chris Terran
All images are copyright and may not be reproduced without permission

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