Bad vignetting box around frame

[Mattm45]

I’m having a problem when taking exposures longer than a few minutes, the edges around the frame while shooting are running up into the centre of the photo it’s capturing, with each exposure taken it gets worse and worse, I’m forced to only take exposures less than 10 minutes . Or else my image gets smaller and smaller. What is causing this? Do I need to take my flats? I’m using svbony 405cc cam

[admin]

Hi,

are you using live stacking in SharpCap?

If so then this is relatively normal - if your mount is not quite tracking correctly then the image will be gradually shifting. SharpCap corrects for this by offsetting each new frame to align with the ones already in the stack, but some of the sky that you could see in the first stacked frame will have moved out of view by the 10th or 20th. Those parts near the edges will no longer receive any new data and will start to appear darker.

There are things you can do the reduce/eliminate this - better polar alignment might help give more accurate tracking, or you can try using the 'recenter' feature in SharpCap's Live Stacking 'Guiding' page which can be set up to move the telescope back to the correct position after the drift has exceeded a certain threshold.

cheers,

Robin

[Mattm45]

Hi! Yes I am live stacking while having this issue sorry! That makes a lot of sense now I will try and see if that works thank you!