han59

For testing of my own software, I'm looking for a series of DSLR images of a variable. Is there anybody who could provide me with one or more image series for testing? The DSLR or OSC type of images are required to test the extraction and processing of the green channels correctly. Thanks, Han

After so reading some discussions and guides, the most convenient method to process an DSLR image for photometry would be to combine each 4 raw Bayer pixels R, G1, G2, B into one RGB pixel. But the combining should not happen as the normal Debayer method since the luminance is adjusted using the neighbour pixels. So the RGB green would be simple (G1+G2)/2 and R and B stay the same . That would halve the image dimensions in pixels but preserve the colour information for photometry. This would intuitive be a better method then split an image in four seperate images called R, G1, G2, and B. Bu

As a programmer I'm currently working on new the photometry routine in ASTAP. There are two methods I'm considering for DSLR: 1) One is to extract from raw the two green pixels of each 2x2 bayer matrix and combine them. But since you uses only 50% of the of the image you have to assure that the star size (HFD, FWHM) is much larger then a pixel size. If the peek of the star is at the blue or red sensitive pixel you will get an measuring error. So having a slightly de focused image seems important. 2) The second method is to de-bayer and then extract the green. Probably less reli

Measurement of the SQM is accessible via the command line so SGP could read it. In principle you could also get a good indication via the image background value if you keep the exposure the same, so I don't think it is essential to monitor it all the time. It is more to get an absolute reference value for a site. It will work even with H-alpha filter as long the image background is increased b y the sky background. So at my site, SQM=20.4 best and 200 seconds exposure it works. The value differ slightly compared with broad band subs. 30 minutes sub, could work but the image sho

Nina is testing for the G databases. They removed that in the latest nightly build. There was no need for since this will be done by ASTAP. The new H databases are faster. So in the long term it is better to switch to the H version and remove the G versions. Han

For the record: Today I looked more in detail to atmospheric extinction. The likely reason that the Unihedron and ASTAP reported values are very simular is the fact that the Unihedron calibration is about 0.35 magnitudes corrected. This is equal to the extinction in the zenith: http://www.lightpollution.it/download/sqmreport.pdf

The reference are the stars. Like the Sun they are fainter near the horizon due to extinction. So the ASTAP SQM value will be lower at lower altitude/elevation because the stars are fainter as at zenith and therefore the sky background will be seen as brighter. The difference between zenith and 45 degrees altitude/elevation is maybe 0.12 magnitude but at zenith there there is still an extinction of typical 0.28 magnitude (depending in humidity and observer altitude) . I didn't measure that difference for unknown reasons, but it will be interesting to see if the values from the Unihed

Just realizing that altitude and transparency plays a role. Measurements where done at zenith. At lower altitudes the stars are fainter so probably it is better to talk about relative SQM value. So maybe it is a coincidence that the values are so close.

The ASTAP measurment doesn't require an external calibration. After solving you can measure the "star flux/(2.51^magnitude)" ratio using the star database and this value will be constant. Outliers and saturated stars will be ignored. With the "star flux/(2.51^magnitude)" ratio you can precisely express the background signal in magnitude per square arc second. So this measurement doesn't need calibration. It is calibrated each time against a star database. Dirty optics or aging has no influence as with the Unihedron meter. As long the CCD or CMOS sensor is linear it will work. Mayb

The free ASTAP program version ß0.9.480 has a new experimental option to measure the sky background accurately in magnitudes per square arc second . This is the same value as reported by portable Unihedron SQM meters. As soon an image is solved, the program can calculate the link between measured star flux and the star magnitude from the database. This flux/magnitude relation can also be used to measure the sky background value. The achieve the highest accuracy a pedestal values can be entered which is the same as the mean value of a dark/bias image. Below the first resul

A new version (0.9.74) of the free CCDCiel program has been released. With this program the imaging of deep sky objects can be fully automated. But it is also possible to manually operate the different steps. There are Windows, Linux, Linux RPi en Mac versions available. In this version the sequence routine has been optimised and improved. Editing the sequence while running is possible. For me this is a great version and the preliminary versions where a pleasure to work with. Han Webpage: https://www.ap-i.net/ccdciel//en/start Announcement of the new version: https

I suspect you downloaded the new database H17 and the program on the day the ASTAP program was upgraded from G17 to H17 databases. So a transition period. For the H version of the database you will need version 0.469 or higher. I would suggest to install the latest ASTAP program and try again. Databases are simply installed in the same path as the program and normally never have any location or path problem. The only time access problem occur is in very rare cases where a second ASTAP is still in memory searching and they try to access the same database. Task manager will show that. For

Even with uneven spaced holes, you still should be able to center the secondary.

Thanks for the image. I have analysed it in (my) ASTAP using the same image orientation. The values are difficult to compare. The average HFD is 6.6 or 10.8"which is comparable with the CCD inspector value. In ASTAP the tilt and curvature are expressed in delta HFD and not in %. The tilt is delta HFD 0.23 equals 0.12*1.63"=0.19". The curvature so the difference between center and outer areas is 0.7 HFD equals 1.12". The strange thing is that all stars are oval as also indicated by the PI image. Must be optical imperfections. The star ovality will skew the measurement. Maybe it is

It is pretty sharp image and full of stars. I'm interested to try it in the ASTAP inspector to compare. Can you share the full resolution in FITS format? Han