Telescope: Orion 80ED apochromatic
refractor at f/7.5
Focus: Prime focus
Filter: Astronomik Hydrogen Alpha
13nm FWHM (Luminance), LPR Filter (RGB)
Mount: Vixen GPD with Skysensor2000
Camera: Modified Canon EOS 300D, at
Guiding: 700mm refractor guidescope,
SAC7 camera, autoguided with Guidedog software
Exposure: Total 70 mins (Luminance)
and 38 mins (RGB)
Date: 28th & 29th July 2005
Processing: RAW file conversion,
Offset and Dark subtraction, flat fielding, registering and stacking done in
IRIS. Used the asinh function to enhance colours. Curve stretching and a
little unsharp masking in Photoshop CS. Composited with the Luminance image using a
technique described by Rob Gendler
(Method 2) then
colour saturation enhancement with Luminance Layering. Noise reduction
in Neat Image.
I'm impressed with this inexpensive
telescope, at least for narrow-band imaging! At the centre of the
field, stars are tight and sharp. With rescaling to 50% (not enough to
squeeze 6 megapixels onto the screen), the image shows very good sharpness.
Note the fine detail visible.
Below are crops, from left, the centre of
the field, top left, and bottom left - all at 100% scale.
The centre is superb. Stars are
often just 2 pixels across. However coma is evident at the corners at
100% scale, but look acceptable at 50%.
I'll reserve judgement on RGB performance,
however. I noticed that the blue and green frames showed out-of-focus
stars, whereas red was in focus. This may be due to IR light leaking
through the microlens filters and into the G and B frames. I have
placed an order for an IR block filter and will soon see if this hypothesis