Some difficulties with QHY camera

[Jean-Francois]

Hello Robin,

in an old message, it was the discussion about the FWHM values of the Live Stack ...
With the very last beta version ... I have very high value of 8 or above the scale, but the real spot of my RASA is around 2.5 to 3.0 pixels.
It is too much ... if the green bars are above the full scale

Other problem with my QHY cameras is the cooler set temperature.
I have on 3 different cameras.
I guess that I found where it comes from ... in live view, no problem, but if I set "Force Still Mode", then it is very difficult to set the cooler temperature. I need to try different temperature 5 to 10 times until it takes the new set point.

I'm now trying to optimise the RASA-camera distance with some shims (2x 0.5 mm shims).
I used the Collimation tool ... It is still experimental since years ... do you plan to update it ?

Regards,
Jean-Francois

Here an image of my test ...
Region around Sadr star. Instrument RASA8", camera QHY268 mono with Baader Ha F#2 filter, high gain mode at gain 150.
Stack of 60 images of individual 30s exposure for 30 minutes stack.
Live Stack with SharpCap with only dark image subtraction. No guiding.
No other processing except saving the PNG image in JPEG with 70% reduction (1MB image limit).
Note that the white level of the image could be not optimal, while I'm outside near the telescope with the laptop monitor at lowest intensity level.

Stack_60frames_1800s_WithDisplayStretch.jpg (1017.14 KiB) Viewed 136 times

[admin]

Hi Jean-Francois,

could you send me one or two raw images from the telescope so that I can see why the FWHM readings are odd please? I have tests in the code that check the FWHM reading by making artificial star images with known FWHM values and then measuring them to check that the value comes out close to the known value. Those work, so something interesting must be going on to throw the measurement in more real-world cases. The most likely cause is a failure to properly estimate the background near the star, which, if underestimated, would leave the star looking much wider than it should.

As to the collimation tool, I've not really got any plans to continue with that approach to collimation. When I was testing it out myself, it worked nicely on a newtonian with no coma corrector and a large FOV camera, but nobody actually images like that. If you put on a coma corrector then the results were rubbish Essentially, the signal that the tool is trying to look for is only significant in cases where the edges/corner are badly impacted by optical aberrations ...

cheers,

Robin