Irydeo Observatory

Irydeo Madrid (MPC Z41)

  1. Observatory
  2. Mount and telescopes
  3. Cameras
  4. Control software

Observatory

Many amateur astronomers find that setting up a small observatory at home, even without an ideal sky, offers greater immediacy and consistency in their observations.

However, in my case, it has not been a straightforward task. From the initial design, specific challenges arose that needed resolution, and it took time for it to become fully operational, going through periods of minimal progress and setbacks along the way.

Finally, the dome was discarded, and the observatory was designed with a sliding roof system. This system is simpler and, in my situation, less problematic in many ways. The roof is operated by the Talon6 system, ensuring reliable performance.

Telescope and Mount

A system configured in an equatorial arrangement with direct friction transmission and 23-bit absolute encoders has been chosen.

This mount, designed and developed under the name JTW OGEM (Open German Equatorial Mount) in 2018, has a long and complex history. After a long wait, it was finally installed in 2023. It has an ideal load capacity for the CDK and works as expected.

After a thorough analysis, we concluded that a 17" aperture telescope featuring a popular configuration today—a classic Dall Kirkham with corrective lenses (CDK)—is the most suitable option. This instrument is designed and manufactured by Hubble Optics. It may not be as cool as other brands, but it delivers magnificent performance.

  • The jump from a 30-centimeter telescope to a system with a 43-centimeter primary mirror (and slightly less secondary obstruction) offers a 130% increase in actual collecting surface, making it easier to work with high magnitudes in both photometry and spectrometry, which the previous system struggled to achieve.

    The light collection depends on the surface of the primary mirror and the central obstruction created by the secondary.
  • The corrected field is around 70mm, being ideal for quality astrometry.

    Field and vignetting correction of the system at native focal length.
  • This system has a native focal length of 2937 mm (f/6.8), with various options to significantly reduce it. In our case, we opted for a Takahashi CR reducer 0.73x, which provides a corrected field of 44 mm. As a result, the telescope has a focal length of 2144 mm (f/4.96) and a field of 36x36 minutes with the QHY42, slightly larger than the 32x32 of the previous RC300. The resolution also decreases to 1.06"/pixel, which is, in my experience, very suitable for the observatory sky.

    Takahashi CR 0.73 reducer, designed for the Dall Kirkham corrected mirrors, such as the Newlon CRS.
  • Its optical design is simpler, based on the Dall-Kirkham configuration, featuring an elliptical primary and a spherical secondary, with a doublet added to correct the aberrations of the original design. Consequently, collimation is straightforward. After more than 15 years of working with Ritchey-Chretien systems or similar designs, I admit I became quite comfortable with them; however, I cannot ignore their extreme sensitivity to excellent mechanics and the demanding nature of their collimation, which results from having two hyperbolic mirrors. These CDK systems, with a spherical secondary, do not have their inclination affect collimation, as long as they are aligned on the optical axis, making the process trivial.

    Optical design of the Dall Kirkham Corrected (CDK)
  • Unlike other options, the selected design employs a sandwich mirror, resulting in a significantly shorter acclimatization time (about 10 times) and a weight reduction of roughly 20-25%, which is valuable for these behemoths. This becomes critical with these already substantial apertures, where insufficient acclimatization can make a system unusable throughout the night.

    Here we see the primary mirror up close, with its sandwich design.

    To complement the large CDK17, the observatory features a Rowe-Ackermann Schmidt Astrograph 11 (RASA) with a short focal length of just 620 mm (f/2.2). This telescope has an 11" aperture and is based on classic Schmidt cameras, marketed by the renowned Celestron company.

In addition to being an outstanding astrograph, its primary focus is the identification and monitoring of asteroids and/or comets with uncertain orbits.

Cameras

QHY42Pro

As a camera specifically designed to work together with the 12" telescope, a QHY42Pro is used, which is based on a sCMOS GSense 400 BSI with a size of 22.5mmx22.5mm (diagonal of 31.9mm).

qhy42-f

You can find more information in this small review

QHY268M

The QHY268M camera has been chosen for use with RASA 11. It features a 16-bit Sony IMX571 APS-C CMOS sensor, with a diagonal measurement of 28mm and a resolution of 26Mp at 3.76μm pixel size. When paired with the telescope, it provides a considerable and well-corrected field of view of 2.18x1.46 degrees.

You can find more information in this little review.

Filters

I typically capture without any filter, as the goal is to achieve the highest possible magnitude, such as in NEOs or very faint supernovae. However, the system is equipped with two filters, mainly designed for photometry:

  • Baader Bessel V filter, a classic essential for photometric work.

  • Infrared pass, although primarily intended for planetary photography, I am using it in a completely different way to track comets, asteroids, and supernova research, as it effectively filters out significant light pollution and darkens the sky considerably.

Control software

Even though I'm at home, the observatory is automated. I try to use free software as much as possible, which, unlike years ago, we are lucky enough to enjoy in amateur astronomy with great quality and stability.

The central element of control and automation at the observatory is CCDciel, a magnificent multiplatform free software developed by Patrick Chevalley, who is also the author of Skychart. With a simple interface yet packed with advanced options, it has become essential software in my daily routine.

Observatory

ASTAP is also used in short-shot substacking, a very useful technique, as I have mentioned, in sCMOS such as this QHY42Pro (especially for transit photometry) and which the author implemented at my request.

In the photometric analysis, I use AstroImageJ, a sensational free software, which I think is undervalued in our world, but with some routines, which, especially in differential photometry, are very remarkable.

The heart of my astrometric work is Tycho, focused on the analysis and search for asteroids and NEOs, essential.

As a curiosity, all the analysis and processing software runs on Debian GNU/Linux, including Tycho, which runs under Wine and supports 100% of its features, including OpenCL acceleration on native GPU.

Tycho