Indents after stacking in DSS and stretching in PS

[Dave2292]

hello,

i have an issue with what i am assuming is my flats, they seem to leave an almost indent looking blob where the dust would of been.

 

my flat taking process is as follows:

slew telescope to point straight up

stretch white t shirt over top

apply light box at a low setting

put dslr in AV mode and use backyard eos flat mode to capture flats

 

now i do refocus slightly mid shoot as the temperature changes but i have read a few times that this shouldn't cause any problems.

i can add a picture if it helps.

 

any help is appreciated, thank you for reading. 

[vlaiv]

Image would be helpful.

"bevel" type of issue happens if dust particle moves. Sometimes it can happen if camera rotates - but that will affect dust shadows differently across the frame. If single dust doughnut is affected - that dust particle moved. If whole frame is affected -  then something strange happened - as if whole flat frame moved a bit (maybe it was somehow aligned in stacking - no alignment is needed for flats).

Under/over correction happens due to improper calibration or light leak of sorts (same image of dust doughnut but brighter or darker).

Change of focus will cause outline type of error - doughnut will be calibrated but its edges will be beveled.

 

[Dave2292]

28 minutes ago, vlaiv said:

Image would be helpful.

"bevel" type of issue happens if dust particle moves. Sometimes it can happen if camera rotates - but that will affect dust shadows differently across the frame. If single dust doughnut is affected - that dust particle moved. If whole frame is affected -  then something strange happened - as if whole flat frame moved a bit (maybe it was somehow aligned in stacking - no alignment is needed for flats).

Under/over correction happens due to improper calibration or light leak of sorts (same image of dust doughnut but brighter or darker).

Change of focus will cause outline type of error - doughnut will be calibrated but its edges will be beveled.

 

Here is a an overly stretched image as a quick reference, they do get worse than this in some images but i haven't saved them.

what i think i may have noticed is the more sessions i add to deep sky stacker from different nights and different flats for each group, it seems to get worse

[Dave2292]

51 minutes ago, vlaiv said:

Image would be helpful.

"bevel" type of issue happens if dust particle moves. Sometimes it can happen if camera rotates - but that will affect dust shadows differently across the frame. If single dust doughnut is affected - that dust particle moved. If whole frame is affected -  then something strange happened - as if whole flat frame moved a bit (maybe it was somehow aligned in stacking - no alignment is needed for flats).

Under/over correction happens due to improper calibration or light leak of sorts (same image of dust doughnut but brighter or darker).

Change of focus will cause outline type of error - doughnut will be calibrated but its edges will be beveled.

 

Here is a much better example, this includes about 4 groups with there seperate flats and stacked in different groups within deep sky stacker

 

Edited April 29, 2022 by Dave2292

[vlaiv]

I see what you mean, and I don't really know what could be causing that.

Could you include master flat for top image (assuming it is single session) for comparison?

[Dave2292]

it is strange, the way i use deep sky stacker with groups is like this (as deep sky stacker is odd)

main group has my bias master and then each group after includes its separate flats and lights (don't use darks)

the top image is two separate sessions unfortunately.

[vlaiv]

40 minutes ago, Dave2292 said:

it is strange, the way i use deep sky stacker with groups is like this (as deep sky stacker is odd)

main group has my bias master and then each group after includes its separate flats and lights (don't use darks)

the top image is two separate sessions unfortunately.

Maybe something strange is happening in DSS?

Try just stacking one session with one set of calibration frames to see if you'll get same issue.

[Dave2292]

33 minutes ago, vlaiv said:

Maybe something strange is happening in DSS?

Try just stacking one session with one set of calibration frames to see if you'll get same issue.

hmmm just tried a single session of the pinwheel and they are still there, going to try the other session and see what happens. thanks so far