ETX, gate to the sky ...
There is no best pleasure than having always with you a powerful and compact instrument which allows you to share in very different occasion your astronomical passion.

The ETX scope is one of those. It travels in the plane and is always ready when skies become suddenly clear. Despite its small aperture, the optical formula is excellent for the sun, moon, and planetary observations. For deep sky observations, the classical jewels of the sky are also at your fingers and even more...

The one who are saying this instrument is just for visual observations are just lying. CCD atrophotography is possible. Even with the old "analog" mounting I was able to shoot at jupiter and saturn as you could see below... with a webcam, a digital camera or a camescope, the ETX is so versatile that you have a lot of domain to explore with it.

When I have the possibility to , I mount the ETX to a more robust equatorial mounting, a GP Vixen polaris, equipped with the Sky Sensor, and this becomes a very powerful instrument which can catch deep sky objects as you never though it could possible to make with a so tiny instrument...

Planetary CCD Imaging

Deep Sky CCD Imaging

Sun Web cam Imaging

Planetary CCD imaging

The images has been taken at the Pic du Midi summit. I added a weight on the optical tube to counterbalance the CCD camera. The ETX mounting is the "old-style" one, with no auto-guide or digital control.

The main difficulty was to place the object on the CCD and then to keep it despite the manual alignement of the polar axis. To align the ETX, I did only a polar pointing and no additional adjustment. Regularly, it was necessary to unlock the AD axis and manually re-center the object. Hopefully, as exposure time are short on planetary images there was no effect on the images due to the poor alignement.






Deep sky CCD imaging

The equatorial mount is a polar Vixen GP, with a sky sensor computer. The sky sensor helps for automatic pointing but the accuracy is not enough to have the small object directly centered on the CCD.

Some tricks


The sky sensor can recompute the alignment each time you ask for using the latest object you are pointing. I used the feature on a bright star close to the faint object then I ask for automatic pointing.

The CCD camera is put on the axial output of the ETX. On the other output, I put an eye-piece at a distance which allows to have good focus on both the CCD and the plane. This allows to fine tune the pointing using the eye-piece. The CCD image center is not equal to the center of the field of view, so it is necessary to first center the oject on the CCD then identify the off-center position of the object in the eye-piece field of view.








Sun Webcam imaging

Due to the very high luminosity of the sun images, the webcam is a very friendly imaging devices to use on this object.

The webcam is a Philips Toucam Xpro. The image size is 640x480. The Webcam is put at the eye-piece ouput. In video mode with moderate frame rate (5-15fps) it is quite easy to locate the sun. The focus is made on the border of the Sun. The automatic exposition is set to OFF and adjusted to get a good contrast on the sunspot.

A sequence of few seconds is recorded. Using Iris software, the best images of the sequence are extracted with the wonderful-powerful-extraordinary Iris command "BESTOF" and "SELECT".

I do the image registration using the function PREGISTER. This function was designed to register planetary images, so I used a sun spot as if it was a planetary object and it works...

Sun spots...

In this column is the result of the first added and registered 20 images, filtered with an unsharp mask medium with PaintShop Pro In this column is the result of the selected 20 best images, registered and added, filtered with an unsharp mask (2,2) with Iris. 
The dusts have not been correctly removed, despite some try using an auto generated flat field...