M42 with Vixen ED81S apo refractor
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| Date | : | 07 Jul 07 |
| Optical system | : | Vixen ED81S apo refractor + unmodd Canon EOS 350D body + IDAS LPS filter |
| Effective F.L. & F ratio | : | 630 mm @ F7.7 |
| Mount | : | Vixen GP equatorial |
| Camera setting | : | Jpeg format @ iso1600 w/ NR on |
| Total exposure | : | 10 x 60s + 12 x 20s = 600 s |
| Guiding | : | Unguided |
| Stacking & processing | : | Stacking in Registax 3.0, Level & Curve stretching in Photoshop 7.0. |
| Sky & Air conditions | : | T = 5-6/10 @ temp ~ 8 oC, wind from breeze to occasionally windy |
| Place of photographing | : | Tai Mo Shan in Tsuen Wan, Hong Kong |
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Remark |
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A test shot to see how LPS filter did the job in "killing" light pollution |
Comments after test :
The photographic speed of this little apo refractor becomes very slow, maybe equivalent to F12, when a LPS filter is in use with it.
So as to see how much faint structure in M42 could be captured within the max. unguided exposure of 60 sec at this focal length offered by GP mount, I decided to select ISO speed of 1600 in spite of very noisy image resulted. And so as to do processing in Photoshop more easily, Jpeg format was set too.
LPS blocked light pollution quite significantly and a neutral background sky resulted, which didn't introduce too much work on neutralizing the color of background sky. And exposure per each frame could be even longer.
Though this is not a good image for publication, one thing has convinced me that with help from a LPS, this little apo refractor can do the job very well in deep sky imaging at this spot though it is very severely light polluted by a big town w/population > 0.5 million.
Additionally, this Vixen small apo refractor shows very good optical quality. Better than those chinese made 8cm ED refractors? Justify by yourself.
I believe I can take much better images with this scope next time in countrysides of less light pollution and camera set at RAW mode @ISO400 speed.
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© All images are copyright William L.T. Ng.