Today there was the chance to observe a total lunar eclipse here at Lake Constance! Under a clear sky and at about 28°C after 10 o’clock in the evening the blood moon was perfectly visible. Right below the moon planet Mars was shining brightly. A lot of people were interested in seeing this phenomenon.
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This article is about finding the best possible telescope focus by approximating a V-Curve with a hyperbolic function.
A V-Curve is the result of moving the focus of a telescope from an outside focus position into the focus and then further into the same direction out of focus again. This way a V-Curve comes into existence where the focus position is on the x-axis and the focus measure on the y-axis (right figure). Probably not surprising this curve is called V-Curve since it is similar to a V. There are different ways to measure the focus – for example the “Half-Flux Diameter” (HFD) and the “Full width at half maximum” (FWHM). In this case the I use the HFD measure.
 | Date | 2017/07/20 |
 | Location | La Palma / Spain |
 | Object | Trifid nebula (M20) & open cluster M21 |
 | Camera | Atik383L+ |
 | Guiding | yes, QHY5-II Mono via OAG |
 | Telescope | 8 |
 | Barlow lens | none |
 | Mount | EQ6Syntrek |
 | Cooling | -10°C |
 | Luminance | 8x 600s, bin: 1x1 |
 | Red | 7x 150s, bin: 2x2 |
 | Green | 7x 150s, bin: 2x2 |
 | Blue | 7x 150s, bin: 2x2 |
 | Dark | 2x |
 | Flat | 10x |
 | Total exposure | ~2h12m |
Tonight I decided to image the Trifid nebula (M20)
which is quite “close” to the Lagoon nebula M8 from my last session. The seeing tonight was around ~2.4″ which could have been better – but certainly it was still sufficient.
Back in 2013 I already imaged the Trifid nebula with the same equipment but from Boeblingen. It is interesting to see the difference here.
For post-processing I used the free software DeepSkyStacker and GIMP. The full resolution images is available here.
Clear skies!
Tonight I was able to proof that the “Lagoon nebula” M8 was still there ~4100 years ago – wow! With a teapot, a sunlounger (probably better a starlounger) and the right music the night passed quickly 🙂
The total exposure time was ~1h36m. The seeing conditions were around 2.2″. It was a clear night without wind. I used my 8″ GSO newton telescope with an Atik383L+ camera (see here). And again I am amazed which image quality is possible with this equipment on this dark sky within this short exposure time. Below is just the luminance part of the image which shows some sharp details of the nebula.
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It’s stargazing time on La Palma again – this time from Casa Las Flores. The little house is located in Aguatavar – close to Tijarafe on a height of about 580m. You have a power supply outside the building, free view to Polaris from both terraces and in July the bright part of the Milky Way is perfectly visible between 22:00 and 4:00 local time. Furthermore you have a coffee maker, a table, chairs, a fast WLAN internet connection and a barbecue. What else do you need? 😀
The image is a single frame recorded with an Canon EOS6D in combination with a Samyang 2.8/14mm lens (15 sec. exposure time, ISO4000) . The post processing has been done with rawtherapee.
Tonight I only test my equipment – for tomorrow I plan to record the bright nebula M8 in the milkyway. So stay tuned for the result!
Last updated: June 16, 2022 at 12:10 pm
