M42 with APM 4" F6 semi-apo triplet lens
¡@
| ¡@ |
|
¡@ |
| Date | : | 11 Jan 07 |
| Optical system | : | Homemade 4" refractor using APM 4" F6 semi-apo triplet lens + unmodd Canon EOS 350D body + IDAS LPS filter |
| Effective F.L. & F ratio | : | 600 mm @ F6 |
| Mount | : | Vixen GP non-goto equatorial mount |
| Camera setting | : | RAW format @ iso800 w/ NR off |
| Total exposure | : | 22 x 30s + 12 x 20s = 940 s |
| Guiding | : | Unguided |
| Stacking & processing | : | Stacking in DeepSkyStacker w/dark frames subtraction, then blending in Registax 3.0, finally Level & Curve stretching in Photoshop 7.0.1 |
| Sky & Air conditions | : | T = 5-6/10 @ temp ~ 9 oC and breezy |
| Place of photographing | : | Tai Mo Shan in Tsuen Wan, Hong Kong |
|
Remark |
: |
A test shot to see how quality difference it was between RAW format and Jpeg |
Comments after test :
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.
ISO speed of 400 should be better but finally choosing ISO800 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.
Maybe sky conditions not so ideal or because of my poor processing techniques, I didn't see any big benefit from RAW format over Jpeg.
Moreover, control of chromatic aberration of this lens was not so good. The stars looked a little fat with some blue halo around them.
One thing has convinced me that with help from a LPS, deep sky imaging can be done at this spot, though it is just next to a big town w/population > 0.5 million. This place is about 1/2 hour drive from my house.
I believe better images can be captured if a better scope is used and longer exposure @ISO 400 is taken with guiding.
| Star Field Gallery | Deep Sky Gallery | Webcam Planetary | Lunar Gallery | Comet Gallery |
| Newest from Vixen | Vixen Telescope | Tat's Machining | Tat's Specials | For Sale Corner |
© All images are copyright William L.T. Ng.