wimvb

Rule of thumb and experience from an earlier life in the semiconductor industry. So far, I haven't seen linearity diagrams for sony cmos sensors.

Basically, yes. But saturation effects, or rather, non linear response is subtle. A sensor’s response can become non linear long before a pixel is ”full” or saturated. In the linear response region, an increase of, say, 10% in the input signal results in a 10% increase of the output. In the non linear response region, the increase in output is less than that, but still more than 0%. In the true saturation region, any increase in input signal will not result in a change in output; the pixel is truly full. When taking flats, you need to be well outside of the non linear region, not just the saturation region. Usually being at half of a sensor’s maximum output (30 000 ADU) is ok, but lower can be safer.

Have you watched Adam Block’s youtube videos on wbpp? Might be of help

If one colour is stronger than the others, their average or median may be low, but the strongest colour may become saturated. Saturation in camera sensors is not abrupt but gradual. In an osc, the master flat isn’t debayered, and the average and median are calculated for all pixels together.

The 14 bit output of a sensor is stored in the high bit range of the 16 bit image files. So, pitch black is 0 in 14 and 16 bit. The next light level is 1 in the 14 bit ADC output, and 4 (100 binary) in the 16 bit image file. Then 2 in 14 bit and 8 in 16 bit, etc. The brightest level is 16000 (rounded) in the 14 bit ADC, which becomes 64000 (rounded) in the 16 bit image file. So, 30000 in the output image file, is actually 7500 in the ADC output of the sensor. But depending on the camera or settings, that is not necessarily in the linear response range of the sensor. Especially since the 30000 value is an average of the entire image. The central region of the image (and local pixel response) may very well be a bit higher.

How do you calibrate your flats? Overcorrecting flats can be caused by poor flat calibration. With a cmos camera, you need to be very precise with calibration. Keep the exposures such that the sensor is in its linear response region (for me that is the case when I aim for 25000 ADU). Use a colour neutral light source if possible. If not, make sure that the three colour channels in an osc are all in their linear response region. Keep the camera at a constant temperature, gain and offset. Shoot flat darks at the exact same settings as your flats. Flat darks that don't match flats, can leave an offset in the master flat that will result in over- or undercorrection during light frame calibration.

The asi120 is ok for guiding probably, although I get better results with an asi290 on my oag. But it is most likely too small for alignment with plate solving. For polar alignment with plate solving to work smoothly, you will need a fov of 1 degree or preferrably larger. I've done it with a smaller fov, but had more fails. If you can use your dslr for plate solving, then use that.

Nice to see you here, Gina.

Synscan hand controllers have a built in all star polar alignment tool. But if your mount is level, and you make sure it's level onnthe new lication, you shouldn 't need to change altitude at least. Use a compass to get azimuth approximately right. In the ballpark may be enough. As long as you use a guide rate less than 1, RA will never change direction and backlash reduction isn't necessary. That's why there is no backlash routine in phd for RA. You decrease backlash by feel first, as you did in DEC. On the outside of the mount housing there are smal round black covers, behind which is the worm gear. Two covers (one on each side) near the DEC gear and two near the RA gear. The backlash assembly grub screws are on the sides between these covers. The grub screw nearest the covers will back off the worm when tightened. See the photos in this thread.

Not blown out I hope, because that would mean you're in the non linear region of your sensor's response, and may very well be the reason why flats won't work and leave a pattern in your images.

Stars do look good in the image. You can also see that your DEC guide pulses (red) are all in the same direction. As long as they are, the DEC axis never needs to reverse direction, and you won't notice DEC backlash. You also have a total guiding error of only 0.53 arc seconds, which is very good. I would suggest you leave the DEC assembly where it is. " if it ain't broke, don't try to fix it" applies here. But if you do get jumps or erratic behaviour in DEC, you know where to start looking. have a look at the Polar Alignment Error. 767472.4 arcminutes make no sense (there are only 21600 arc minutes in a full circle, 360 degrees). This is an indication that the guiding assistant results are not valid. Probably because you were pointing due North. And that's why this isn't valid either.

This will actually increase backlash. The DEC worm is at the south side of the mount when it is in its parked position. If you the turn the North grub screw counter clockwise, you loosen it. The grub screw will move towards you (North) and away from the worm assembly. This image from Astrobaby's guide shows what I mean. The North grub screw is the one on the right. The South grub screw is the one on the left. The small blue arrow indicates that the left screw is being tightened (clockwise). The large blue arrow shows the movement of the DEC worm housing (dotted line). The DEC worm is fixed in this housing, so it will move to the left as well, coming loose from the main DEC wheel. The main DEC wheel (brass colour) is stationary. When you tighten the North grub screw, the opposite movement happens. The DEC housing with the gray worm moves to the right, decreasing backlash. In the picture all brass coloured objects are fixed. If you tighten the right hand side grub screw (small red arrow), you would normally screw it in. But since it already pushes against the brass pin, it will actually pull the entire housing, together with the gray worm, towards the right. This pushes the worm against the DEC wheel. You always start in a position where you have backlash which you can barely feel. From that point on, only make very small adjustments. You should run guiding assistant with the scope pointing South, not towards Polaris. Near Polaris it is impossible to guide, because it is where all RA lines "come together". So, you calibrate and use guiding assistant with the scope pointing South, but adjust backlash with the scope parked and pointing North. The latter isn't really necessary, but it makes talking about North and South grub screws a lot less confusing. When you use the guiding assistant, you should have the allen screws tightened because they keep the DEC assembly fixed. Without that, the whole DEC assembly is floating, and you can't measure a reliable backlash value. The procedure is Park scope (looking North) Loosen 4 DEC Allen screws a little, so the DEC assembly can move freely Loosen South grub screw, ccw Tighten North grub screw, cw, 1/32 of a turn Tighten Allen screws (Optionally) tighten South grub screw, cw Slew South to Meridian Run Guiding assistant & measure backlash Repeat

It’s easy to clean up those artefacts with a tight star mask. Then mlt or mmt with 2 layers disabled (double clicked). If applied to chrominance, you won’t lose detail.

I think so. when you stretch the image, try to avoid clipping the background. This often creates sn unnatural look.

A brighter background? Perhaps a little less contrast in the galaxy. It makes the image softer. 👍

How did you integrate? Pixel rejection settings, etc. It looks to me that the issue lies there.

Actually, I like the fist image better. Sure it's bright, but has more colour variation outside the bright core, showing brown colour in the dust lanes, and clear blue star clusters. Nr 2 is too "flat" for my taste.

I haven't had this problem, so had to look it up. The only reference I found was this https://openphdguiding.org/man-dev/Tools.htm#Guiding_Assistant But if guiding was active, guiding assistant should run.

Are you guiding when you start the guiding assistant?

ARK - Astronomy Related Kit

It seems strange to me that the raw files are also rotated. But it's a long time since I've used a dslr for imaging, so I won't argue.

Or have the door on the short side.

The jpeg conversion routine in the camera will use the header information to create a rotated jpeg image, but as I wrote before, the raw, uncompressed image files won’t be rotated.

I would think that the raw image files, while containing the orientation information in the image header, shouldn't be rotated.

This is an interesting design, but it looks to me like the side walls are going to be a major obstruction when the roof is open.