Sunday, April 17, 2011

Trying to capture Saturn with a color webcam

The planet Saturn has currently a brightness of 1.04 mag and an apparent size of 19.2". I tried to capture it using my TIS DBK21 One-Shot-Color webcam on my 21cm (f/11.5) Dall Kirkham cassegrain telescope in order to find out the most appropriate focal length for this application. The DBK21 cam uses the same chip as the popular Philips ToUcam 840k Pro. However both the electronics and the mechanical construction are excellent on the DBK21. Considering the low brightness of Saturn (compared to Jupiter, the Moon or the Sun) and the permanent bad seeing at my roof observatory, it was useful to get some experience on using this webcam to capture Saturn with my telescope. The goal is to find the "golden ratio" between the focal length and frame rate to get best possible results on Saturn.


Image 1: a single unprocessed frame

f/11.5 @ 27 frames per second. Focal length was 2415mm. No extenders. Notice: Quick enough to freeze the seeing. Too small planet disc but very bright. No problem to increase the frame rate.

The following data have been calculated with the free software AstroDigital.Net
Model: Takahashi Mewlon 210 (f/11,5)
Focal length [mm]: 2415
Critical Focus Zone [mu]: 290,95
Model: DBK 21AF04
Pixel size [x*y]: 5,6 x 5,6
Chip size [x*y]: 640 x 480
Chip diagonal [mm]: 6,08
Chip surface [qmm]: 18,26
Wavelength [nm]: 550
Telescope illumination power: 1,102345E-05
FOV: 0° 5' 6'' x 0° 3' 50''
Image scale: > 0,48 x 0,48


Image 2: a single unprocessed frame

Image 3: 5000 frames added and processed (AVIStack, Giotto, MaximDL)

Image 4: The setup

f/18.4 @ 19 frames per second. Focal length was 3864mm. The ExtenderNQ (1.6x) of a FSQ-106ED was used. It works excellent on the Mewlon! The planet disk is large and bright enough to show details under good seeing conditions. The frame rate is high enough to freeze the seeing.

Model: Takahashi Mewlon 210 (f/18,4)
Focal length [mm]: 3864
Critical Focus Zone [mu]: 744,83
Model: Takahashi Extender 1.6x
Model: DBK 21AF04/21BF04
Telescope illumination power: 4,306035E-06
FOV: 3' 11'' x 2' 23''

Image 5: a single unprocessed frame

f/28.7 @ 9 frames per second. Focal length was 6037mm. Televue Powermate 2.5x. Notice: Too dark on Saturn, too slow to freeze the seing. Big planet disk.

Model: Takahashi Mewlon 210 (/28,8)
Focal length [mm]: 6037
Critical Focus Zone [mu]: 1818,44
Model: Televue Powermate 2,5x
Multiplier [times]: 2,5
Model: DBK 21AF04/21BF04
Telescope illumination power: 1,763752E-06
FOV: 2' 2'' x 1' 32''
Image scale: > 0,19 x 0,19

Tuesday, April 12, 2011

Backnang's star party 2011

Dear guest, welcome to the photo gallery of our Star Party 2011 .. Backnang, Germany.
The moon is still up and running
Vixen ED102 on a green Vixen GP
Two SkyWatchers are gazing the night sky
Happy faces, good scopes
Most of the guests were observing the planet Saturn at that night. The photo above corresponds to a typical view of Saturn through a big dobson telescope. It has been taken some hours after the event.
A 20cm f/5 newton telescope. Mike said, he had the best view of M42 in his life, as he observed it with this scope on the Alps/Austria 10 years ago.
A Meade LX10 ready to go.
Markus the APOD guy as he sets up his INTES 18cm Maksutov telescope.
Two Lightbridges look the sky.
Gerd at the 76cm dobson telescope. This was once the biggest portable telescope in Europe! John Dobson signed it during his stay in Fellbach/Germany a couple of years ago. It belongs to the Backnanger Sterngucker. You can observe some deepsky objects in color with it! (I'm not kidding!)
The eye of the tiger: a 400mm dobson telescope.
Mike is setting up his unbelievable 30cm dobson telescope.
Dennis with his fine tuned 37cm Dob.
An apple a day ... catches light at night! :-))))

Oh yes! My Nikon and me were also there ;-)

Kind regards and clear nights to the world wide astronomy community from Backnang, Germany. /Panagiotis

Friday, April 01, 2011

Observing Saturn with two different scopes

On March, 3rd 2011 I observed the planet Saturn trying to compare the views through two literally incomparable scopes; a Mewlon-210 reflector with a 25mm TAL Koenig eyepiece and a FSQ106ED (f/5) refractor with a 5mm Tak-LE eyepiece. Since the seeing was terrible and the sky was quite polluted at that night, the view through the refractor were steadier, sharper and more pleasant than through the reflector. However, I could observe one dim star through the Mewlon, that was invisible with the New-Q. Size does matter. The background had the same brightness on both scopes, but the Mewlon was equipped with a Baader Neodymium light pollution filter. I tried to go up with the magnification on Saturn. After trying to extend the native 530mm focal length of the refractor using a perfect Televue Powermate 2.5x, I observed some false color at 265x on Saturn. No, it was not the Powermate. Obviously, visual observers do need the Extender-Q accessory for planetary work. The Mewlon couldn't handle this magnification due to the atmosphaeric conditions.

Two weeks later, I decided to put the dedicated 1.6x NQ extender on the FSQ-106ED and try it on Saturn. Note, this magic part is much more than a simple barlow lens. It corrects the violet/ultraviolet spectrum for photographic applications, i.e. the blue stars do NOT bloat any more. Moreover, it provides a planet-friendly focal ratio of f/8 by also making the FSQ super-apochromatic and hence comparable with the TOA series. High magnifications of 236x are possible with the NewQ extender. Color free.
On Saturn the views are very sharp, crystal clear and a lot steadier than through a larger scope. One can see permanently Saturn's Cassini division on the entire field of view by using a 5mm LE eyepiece. This is amazing and in some way confirms the specification saying it provides a 44m flat field also suitable for photographic use.
Let's go back to the Mewlon again.. In fact, at that night I didn't want to compare it against the Q, since I know the abilities of the μ very well. The views are breathtaking when the seeing conditions permit it. I know what I am talking about. I have observed M13, M11, several galaxies and the planets with this reflector and I still can't forget the views through it. Aperture counts. So, I attached my old DBK21USB on it and I took a videoclip. After processing it with -a great german software piece for photo stacking- I was able to see the current storm on Saturn!!! :-) It's called "the Serpent Storm", see below:
Some astronomers say "the first four inches are the most important" but I think aperture still counts. That's the law of physics. cs px