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Touptek/RisingCam IMX571 (and other sensor) cameras discussion


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1 hour ago, nfotis said:


I am a newbie in DSO imaging (I know only planetary imaging - a bit), but I suppose that in Bortle 8-9 areas like Athens some kind of filtering is required?

It seems that every manufacturer offers its own gain/mode/whatever parameters (and every program has its own idea about acceptable parameter ranges, judging by the NINA thread and native vs ASCOM drivers). This can lead to a real mix-up, if we don't keep carefully notes of parameters etc.



Its easy to think that to combat light pollution you would need a light pollution filter to block this, but hear me out on this little "thought experiment".

What is light pollution? It is mostly street lights, house lights and other types of lighting that allows humans to see at night. Why is lighting a specific colour, usually around the yellow-green-white(if LED, which is also green because blue green and red mixed is white, hence the brightest part is in green that is in the middle) light. These wavelengths are chosen because they are where the human eye is the most responsive. So in this way the least amount of energy could be used to provide the greatest amount of usable lighting at night (for humans).

Now why is the human eye evolved this way? Well as it turns out there is a natural light source, pretty much the only one, that is the Sun. The sun is at its greatest somewhere around the whitish-yellow parts of the spectrum, also where the light pollution filters are blocking most of their light. As a mostly coincidence most galaxies are brightest somewhere around sunlight in colour. This changes a bit, actively star forming galaxies (like triangulum!) are noticeably bluer than the sun, while galaxies with pretty much no active star formation like ellipticals (M87, M32, M110) are mostly blobs of redder than the sun stars. This is because blue stars can only live for a blink of an eye in cosmic terms, so if you see a blue star it must have been born recently, as it will also die very soon. Older galaxies with no active star formation only contain the older smaller stars that are still happily fusing hydrogen for billons or trillions of years. Anyway, point being the average colour of galaxies is somewhere pretty close to sunlight (a coincidence).

So, light pollution filters are essentially "galaxy light" filters also since light pollution and galaxy light is very similar.

The reason why this is not a problem (mostly) is because light pollution is not a sheet of cloth over your telescope that physically blocks light, it is an added colour. And colour is something that is easy to balance out in processing, especially if you have a camera like the IMX571 that has an almost unbelievable colour response with very short exposure times. I should add that it is NOT possible to properly colour balance a shot taken through a light pollution filter, as a big portion of the spectrum is missing.

Here you can see a measured spectrum of M33, a very blue galaxy that is one of the least effected galaxies for light pollution filters. The light pollution blocking bands are mostly between H beta and H alpha, which is most of the spectrum (but not the peak, because M33 is bluer than average).



Edit: Also i might add that it might be possible for local light pollution to be greater than the capabilities of the camera to produce proper colours. In this case there is really no right answer, either take the hit of the LP filter or travel to better skies. But i have really never imaged from better than bortle 6 skies, and most of my imaging is from bortle 7-8 from last winter with an 11 year old DSLR that is nowhere near as good as the IMX571 chip and still it is possible to get proper colour balance without filters.

Edit2: Of course if you intend to image non-broadband targets like nebulae you will greatly benefit from narrowband filters. Well with an OSC camera it would ideally be a duo-band filter like the L-extreme from optolong. Nebulae emit mostly only very specific wavelengths that are easy to isolate from the rest of the spectrum with these filters, and with this method you can gather good data from right under a streetlight, if you want to.

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Got one of these a few months ago. Love it. Worked seamlessly with NINA. Latest image:






Edited by maxchess
missed a bit
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