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Quadruple Star
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| Object : | Capella, or Alpha Auriga |
| Coordinates/Direction : | RA: 05h16m, DEC: +45o59' |
| Object size : | - |
| Object magnitude : | 0.3 |
| More to know : |
Capella, Wikipedia: https://en.wikipedia.org/ wiki/ Capella |
Capella 2024-09-14:
(Click on the image to get one in full resolution in a new window)
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| Date : | 2024-04-15 |
| Time (UT) : | 21:50 to 22:56 |
| Mount : | SkyWatcher EQ6 Pro, beltdrive modified (DIY 2019) |
| Guide : | ASI120 camera with off-axis |
| Lens/telescope : | Pentax 645 FA 300 mm ED f/4 (medium format lens) |
| Corrector/Barlow : | - |
| Field (FOV) : | 6.8x4.5o (full frame) before crop |
| camera : | Nikon D800, QE=0.56, full frame, 36 Mpixel, 14 bit |
| camera temperature: | - , no temperature sensor |
| Film/CCD : | Raw, NEF |
| Filter : | none |
| Control system: | Mount, camera, focus, guide (Ekos) controlled by KStars/Ekos Linux, 64-bit |
| Exp. time : | 59x60 seconds, iso400, dithering every 3th |
| Image process tool : | Siril, Gimp, Irfanview |
| Processing : | flat, photometric color calibration |
| Weather : | some clouds, full Moon, temperature +14 C |
| Site : | Sweden, Stockholm, Hagsätra.
Bortle 9 Free view Az: 20o to 90o, 165o to 185o, Alt: 20o to 55o |
| Comment : | A test image on the star Capella. I wanted some very bright star to give idea how well the camera and optics handle the contrast. This is a 800x800 1:1 crop around the star. One weaker star very close to Capella. |
Focus quality:
Siril which I normally use today when stacking images. It has some tools, this is the plot of how well the stars is focused. One image is bad and got much worse focus, I removed that image before stacking. 
The other images that are left has the FWHM from 4" in the beginning and after one hour it has got out of focus and have a FWHM of 4.66. Already something happened after 40 minutes, not sure what it was. But what does this mean, can I use the photos, or ? One look at the first and last photo. |
Anlyzing the focus on the sub images:
This is the first image in the stack, look at the individual stars how well they are focused. 
This is the last image in the stack, it can clearly be seen that it is out of focus relative the first one. Is it possible to do anything about it ? Earlier I used a temperature compensation system, but it was very hard to calibrate. Another method which I use is to let it auto focus every hour. But as can be seen here it's not enough. Focusing take time and you lose exposure time. It's possible to setup KStars/Ekos to measure the quality of the focus and if needed it do an auto focus. It can be disturbed by clouds, one reason that I don't use it. But I will take a look at it. |
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