Hmmm, what causes this…??

[Stuart1971]

This is a highly zoomed in portion of a stacked image but with no calibration frames at all, with QHY268c at -15,  just wanted to check the data I had, these were 2 min exposures with the Optolong L-Xtreme filter, and guiding was very good, so what causes these hot pixel streaks, the stars are round…??

Now with 5 min subs with just an LP filter I had none of this, so is it purely down to needing longer subs…? 

 

Edited February 23, 2022 by Stuart1971

[scotty38]

Just guessing but dither and/or rejection methods when stacking unless you did the same for both 5 and 2 mins?

[whipdry]

I'd suggest you open the 1st & last frames of the sequence & use Blink, if you see a different in star position between the frames you have your answer! 

BTW your star show a little trialing. 

Peter 

[Stuart1971]

35 minutes ago, whipdry said:

I'd suggest you open the 1st & last frames of the sequence & use Blink, if you see a different in star position between the frames you have your answer! 

BTW your star show a little trialing. 

Peter 

I think it’s the very corners of my images, so not perfectly flat, centre stars look ok….here is final calibrated image of just 53 x 2 min subs, with the L-Xtreme filter….not bad for such a short amount of data…🤔

 

[Roy Foreman]

I get those coloured streakes sometimes when stacking using Deep Sky Stacker, but not when stacking the same data using Afinity Photo so I guess it must be a quirk of the software or its settings. Doesn't happen on all images and I have no idea what causes it.

[Shibby]

It's hot pixel streaks caused by field rotation. Doesn't matter how good the guiding is, if the polar alignment isn't perfect (or the guide star isn't close to your target) you will end up with some field rotation in the corners. The reason they're still present is down to the stacking method - sigma rejection will get rid of them if you have enough subs. Alternatively, you could calibrate with darks or use the cosmetic options in DSS.

[Stuart1971]

3 hours ago, Roy Foreman said:

I get those coloured streakes sometimes when stacking using Deep Sky Stacker, but not when stacking the same data using Afinity Photo so I guess it must be a quirk of the software or its settings. Doesn't happen on all images and I have no idea what causes it.

The coloured streak are the hot pixels from the camera, and as the images moves on the sensor over the period of imaging for a few hours, then when stacked and stars are aligned the hot pixels then form the streaks, but during stacking with all calibration files as you see in the final image above, they have all been taken care of, I use APP for stacking and works really well….

[Stuart1971]

24 minutes ago, Shibby said:

It's hot pixel streaks caused by field rotation. Doesn't matter how good the guiding is, if the polar alignment isn't perfect (or the guide star isn't close to your target) you will end up with some field rotation in the corners. The reason they're still present is down to the stacking method - sigma rejection will get rid of them if you have enough subs. Alternatively, you could calibrate with darks or use the cosmetic options in DSS.

It’s not field rotation, as it’s all over the image in the same direction,  it’s as I just said above…our posts crossed, all gone in final image as shown above too….

Edited February 24, 2022 by Stuart1971

[Rodd]

On 24/02/2022 at 05:16, Stuart1971 said:

all gone in final image as shown above

It is still present in final image--but you have to zoom way in--its chromatic noise.  i get that a lot.  Not sure why.  I always blame my sky.  Binning can help. Having lots of data seems to help