By the end of August 2026, the optical and electronic upgrade of the main instrument at Blahová Observatory—the 28 cm Celestron C11 Schmidt-Cassegrain telescope—was successfully completed. The primary objective of the modernization was to increase photometric precision and achieve full automation of the setup.
The Upgraded Hardware Setup
The core of the imaging system is the Celestron C11 optical tube assembly, operating at f/6.3 with a 0.63x focal reducer (focal length approx. 1764 mm). Precise, temperature-compensated focusing is now handled by a robotic PrimaluceLab SESTO SENSO 3 focuser motor.
Fast switching between photometric bands is provided by a 5-position ToupTek AFW-M motorized filter wheel loaded with 50.4 mm unmounted photometric filters. Image acquisition is carried out using the cooled ZWO ASI183MC Pro camera.
First Light: Multi-Filter Photometry of Comet C/2024 J3
The first operational test of the new setup took place on the night of August 29, 2026. The target was comet C/2024 J3, which was located high in the sky at an altitude of approximately 85 degrees (near zenith), providing excellent atmospheric transparency.
Observations were conducted using three different filters, and data reduction and coma photometry were processed using the KOPR (Software for Comet Observers) software suite.
Observational Data and Results (ICQ Format):
2024J3 2026 08 29.79 V 13.8 AV 28.0T 6a600 1.8 ICQ XX CSO I C 1.83mZCP IM1 KPR 0 U9*0.05 1.2s 1.2 ;Comet Alt.:85.3
Calculated mags: 13.8, 13.8, 13.7, 13.8, 13.8, 13.9, 13.8, 13.8, 13.8
2024J3 2026 08 29.79 g 14.0 AG 28.0T 6a600 1.5 ICQ XX CSO I C 1.50mZCP IM1 KPR 0 U9*0.04 1.2s 1.2 ;Comet Alt.:85.3
Calculated mags: 14.0, 14.0, 13.9, 14.1, 14.0, 14.0, 14.0, 14.0, 14.0, 14.0
2024J3 2026 08 29.80 h 13.0 AI 28.0T 6a480 2.0 ICQ XX CSO I C 2.00mZCP IM1 KPR 0 U9*0.05 1.2s 1.2 ;Comet Alt.:84.6
Calculated mags: 13.0, 12.9, 13.0, 13.0, 13.0, 13.0, 13.0, 13.1
Data Analysis and Physical Interpretation
The multi-filter measurement results clearly demonstrate the physical differences across spectral bands:
UV/IR-Cut / L Filter (V-band reference):
Across the total visible spectrum, the comet's integrated brightness was measured at 13.8 mag with a coma diameter of 1.8 arcminutes. The calculated magnitude series from KOPR (13.8 to 13.9 mag) showed an extremely low standard deviation below 0.05 mag, proving system stability.
Sloan/SDSS g' Filter (Gas emission):
In the g' filter, which targets gas coma emissions (cyanide CN and dicarbon C2), the comet was recorded at 14.0 mag with a slightly smaller coma diameter of 1.5 arcminutes. Measurement dispersion was exceptionally low (0.04 mag).
Sloan/SDSS i' Filter (Dust component):
In the near-infrared band (i' filter), the comet appeared significantly brighter at 13.0 mag with a larger coma diameter of 2.0 arcminutes. This notable brightness excess indicates a strong presence of dust in the coma of C/2024 J3, which scatters sunlight much more efficiently in the near-infrared spectrum.
Conclusion
The operational test of the new hardware components (SESTO SENSO 3 focuser and ToupTek filter wheel) together with software integration was a complete success. The system performed quickly, reliably, and stably. The reduced measurements are being submitted to international comet databases. The next major milestone will be requesting an official Observatory Code from the Minor Planet Center (MPC)!
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