Date: 8/1/2010 – San Bruno, California
Mount: Astrotrac travel system
Camera: Modified Canon XTi with Canon 200mm f/d 2.8 teleobjective (prime lens) opened at f/d 3.5 – at Iso 400. Installed on a tripod collar ring and a Manfrotto ball head.
32 exposures of 90 seconds with Astronomik CLS CCD clip filter, 12 flats frames, 10 darks, 10 biais.
For Flat fields I use an electroluminescent panel from Glowhut. This is by far the best way I found to take flats that “work” in a consistent way.
This is my second try at this with the same set up. I got much better results this time…. Even though it is taken from my backyard where usually magnitude 3 stars are barely seen. Transparency was a little bit better than usual – I would say between 3/6 and 4/6 (magnitude 3.5 stars seen at best) and M8 was quite low (below 30 deg.) so imaging was still a challenge!
The big difference with my previous posting is that my Canon XTi has been modified (Standard IR filter replaced with an astrodon IR filter by Hap Griffin) – and the response of the camera in the Red and especially HAlpha wavelength is much better…
Also this time I made sure the astrotrac polar scope had a centered reticule for better polar alignment.
I used the sane CLS CCD anti pollution filter, same digital processing, and same exposure time as in my previous try. The Astronomik CLS CCD works wonderfully with the modified Canon.
But this time I also used an “X-Tend a Sight mount” from Photosolve along with an Orion EZ Finder. It really helps to find and approximatively center the objects in the canon 200mm field of view since seeing stars through the Canon XTi is almost impossible. Then I take a short shot and re-center the object.
In addition I used a Bahtinov mask as a focus help. Focusing the Canon 200mm open at f/d 3.5 is really hard: in a fraction of a turn stars get out of focus. I found the mask to be of some help in getting more consistent results (even though you do not obtain the usual diffraction patterns you observe when focusing a telescope with the mask).
Processing:
- MaximDL5: darks and flats subtraction, alignment and averaging
- Photoshop CS4: stretching, selective sharpening
- Noise Ninja: noise removal
M8 and M20 – Canon 200mm Teleobjective and Modified XTi
Details of M8/M20- Cropped image
The following objects can be seen in the field of view: M8, M20, M21, diffuse nebula Ngc6559, globular clusters Ngc 6544, Ngc 6553, open clusters Ngc 6530, Ngc 6546
Skytools 3 Atlas
