Bad Flats

[Rodd]

I do not understnd why my recent flats did not work.  Previously, I have had issues with teh filter wheel not positioning the filters precise enogh--which can result in dust bunny movement.  But that always happened after I rotated the filter wheel before taking flats.  recently, I shot 2 groups of flats one group with histogram at about 1/2 the other group with histogram at about 1/4.  I then proceeded immediately to collect my subs--there was no filter rotation, no adjustments of any kind.  All dust bunnies were removed except one for both calibrations.  I don't understand what I must do to get good flats.  That one dust bunny is terrible.  Its a luminance stack and I think I can clone it out--besdies its a galaxy image and I only need luminance for the galaxy--so the blemish can be avoided.  But it still should not be there.  The fact that I collected two sets of flats of different levels that had identical resuls tells me it isn't the flats.  I just don't get it

[newbie alert]

Try about a third of the histogram or adu range

If you use Apt or Nina both have a flats tab

Edited August 1, 2022 by newbie alert
Added info

[ollypenrice]

It couldn't be a tiny mobile bug? I once had this. I could actually see it move from flat to flat but, bizarrely, I was never able to find it physically.

Then again, I think most of us have had problem flats for which we never found a solution. Do 'em again! This game is not as logical as some would have us believe...

Olly

[Rodd]

1 hour ago, newbie alert said:

Try about a third of the histogram or adu range

If you use Apt or Nina both have a flats tab

I don't think its the brightness.  1/3 is what I like to do--but I have found .2 to .5 works.  

[Rodd]

18 minutes ago, ollypenrice said:

It couldn't be a tiny mobile bug? I once had this. I could actually see it move from flat to flat but, bizarrely, I was never able to find it physically.

Then again, I think most of us have had problem flats for which we never found a solution. Do 'em again! This game is not as logical as some would have us believe...

Olly

Not a bug in this case.  the last time that happened to me I took off the focuser to access the reducer (I added a crayford to the vback of the C11Edge and took it off to clean teh reducer before installing an OAG) and there was a nest of ants in my system!  That was bizzarre.  I COULD see them moving about in some frames and it did screw up the flats.  This time it is definitely a dust bunny that was not wholly removed.  I guess its possible that a piece of pollen or dust alighted on a surface of my system after I took the flats.  I might have the opportunity to image tonight/tomorrow--I will try and take them again.  I used to be able to use flats for weeks, but ever since I started using the ASI 1600 with the filter wheel that does not register precisiely, I have to collect flats before any filter change and before powering down.  Collecting them at the start of the night should be perfect.  Even THAT didn't work.  Maybe since it has only been a few days new ones tomnight will work.  

For another bizarre tale: I opened the PA port so I could use my polar alignment scope and two beedy eyes were staring back at me.  there was a mouse nestled comfortably in my mount!.  Fortunately by the time I returned from the house armed with a tool to grab him, he was gone.  I removed his nest.  

[newbie alert]

9 hours ago, Rodd said:

I don't think its the brightness.  1/3 is what I like to do--but I have found .2 to .5 works.  

Ok reading further on sounds like you could have a physically moving flat, literally...

So the dust that wasn't removed can you see it in the individual light frames, or does it get lighter or darker once offset

[bottletopburly]

Maybe the problem is not in the flat but in the flat dark/bias  , have a watch of Adam blocks video it’s in three parts I found it very informative, using cmos cameras Adam recommends flat are at least 3-5 seconds long for cmos cameras, 

There is also another one I watched which may also be helpful which this one may actually help you with your issue 

 

Edited August 2, 2022 by bottletopburly
Another video added

[Rodd]

5 hours ago, newbie alert said:

Ok reading further on sounds like you could have a physically moving flat, literally...

So the dust that wasn't removed can you see it in the individual light frames, or does it get lighter or darker once offset

All the other dust bunnies were removed perfectly, though. So I don’t think there was a movement issue.  Maybe the piece of dust fell over, or something 

[Rodd]

10 hours ago, bottletopburly said:

least 3-5 seconds long for cmos cameras, 

 

This is surprising, and not easilly done for broadband--especially Lum.  For Narrow Band it is easy enough.  But I don't really see this being teh cause of one dust bunny being missed.  I can see it effecting fine scale stuff across the image--and maybe it would really help with speckling.  

[bottletopburly]

Can you see the dust bunny that’s not removed in the flat frames and master flat ?

[Rodd]

10 hours ago, bottletopburly said:

There is also another one I watched which may also be helpful which this one may actually help you with your issue 

I liked this one more--but it didn't really solve my problem.  basically, the video is used to explain that there is a problem with the master flat, which I already know.  The question is what and why and then what can I do.  The other question I have is when he sais "something changed" in teh system so teh flat is different--does that include ADU levels?  When shooting sky flats, the ADU levels are constantly changing as teh sun sets.  That's why short flats are good--I can take 100 flats in 50 seconds--so not much ADU variation--but still some.  I don't think that matters and that he is referring to changes in the light path (reflections, reduction, extension, tilt, movement of a physical elememnt, etc).  Since my flat came out perfectly except for one dust bunny, I am left with the conclusion that  the dust particle changed, somehow.  Maybe an ant ran out between flats, tilted it, then ran back so he wouldn't get imaged.  I wouldn't put it past them.  They are good friends with the gremlins.

[Rodd]

8 minutes ago, bottletopburly said:

Can you see the dust bunny that’s not removed in the flat frames and master flat ?

I will have to take a close look--I am sure its there.  It does not take much of a changein position to cuase issues.  The dust bunny in teh image is not complete like a dust bunny in a flat--like a donut.  It looks defromed as the result of parts that were under or over corrected, which is a hall mark of movement and a misalgnment of the feature between flats and lights.  Like when a filter rotates a little, or the filter wheel doesnt align perfectly.  The fact that its one domut out of dozens tells me it has to be something about teh individual feature that moved.  One thing is certain--the dust particle probably moved during light frame aquisition, which was 6 hours compared to 50 seconds.  Maybe I will calibrate batches of subs--say in groups of 10 to see if I can pin down when it moved.  I don't see what else it could be.

[bottletopburly]

2 minutes ago, Rodd said:

Maybe I will calibrate batches of subs--say in groups of 10 to see if I can pin down when it moved.

Sounds good 👍 

[Rodd]

6 hours ago, bottletopburly said:

Can you see the dust bunny that’s not removed in the flat frames and master flat ?

NO!!!!!  Bizarre. There isn’t a dust bunny close to the spot in any flat I took. And now I have taken many. Just redid them. The flats look identical. What can this be?

[bottletopburly]

Have you tried stacking in another program just to see if they come out the same ?

[Rodd]

4 hours ago, bottletopburly said:

Have you tried stacking in another program just to see if they come out the same ?

No.  

[Rodd]

On 01/08/2022 at 15:55, ollypenrice said:

It couldn't be a tiny mobile bug? I once had this. I could actually see it move from flat to flat but, bizarrely, I was never able to find it physically.

Then again, I think most of us have had problem flats for which we never found a solution. Do 'em again! This game is not as logical as some would have us believe...

Olly

 

On 02/08/2022 at 14:08, bottletopburly said:

Can you see the dust bunny that’s not removed in the flat frames and master flat ?

I found it--I think.  Last night I go to slew north to center a star and the movement was at some obtuse angle--I could not figure out why.  Then it dawned on me....the camera had rotated.  Only one way that happens with threaded connections--something unthreaded.  Sure enough, one of the threads had gotten loose and the camera was rotationally wobbly.  It still doesnt explain why only one dust bunny was effected, though.  

[Rodd]

On 01/08/2022 at 15:55, ollypenrice said:

It couldn't be a tiny mobile bug? I once had this. I could actually see it move from flat to flat but, bizarrely, I was never able to find it physically.

Then again, I think most of us have had problem flats for which we never found a solution. Do 'em again! This game is not as logical as some would have us believe...

Olly

 

On 03/08/2022 at 02:20, bottletopburly said:

Have you tried stacking in another program just to see if they come out the same ?

No again.  I tightened up everything and reshot new flats before collectring a couple more hours of luminance.  The new subs have the defect in the exact same spot!!!Whatever this thing is on the filter, it won't flat out.  I know its on the filter becuase the other filters do not have it.    Funny thing is, it is very very faint on the subs--can't see it.  Even on the master flat it is very faint but you can make it out--but in the calibrated stack it sticks out like a sore thumb.  I am totally confused.  I shot new flats and collected new subs.  How can this be?

[bottletopburly]

Try  turning the glass in the filter and see if the artifact  moves accordingly, at least you would confirm the filter is at fault or not.

[Rodd]

5 hours ago, bottletopburly said:

Try  turning the glass in the filter and see if the artifact  moves accordingly, at least you would confirm the filter is at fault or not.

That would mean taking the camera off and dissaembling it.  I might as well clean everything then.  That is not something I would do in the middle of an image--it will require too much work and I won't be able to find the exact alignment.  I already have a slight rotation in subs after the retightening of teh camera.  It took me about 30 min to achive this.  30 min on teh best night of the year..  I already know that the spot is only very faintly visible on a master flat, while other belishes are very pronounced, to be expected.  The question is not where this thing is, but why it won't flat out and the other blemishes do.  There only can be limited eplanations for this.

[bottletopburly]

Try a  longer sub with higher Adu value of around 22k just to see .

[Rodd]

12 minutes ago, bottletopburly said:

Try a  longer sub with higher Adu value of around 22k just to see .

Now that I can do.  unfortunately, I wont get the chance for a month of so.  Rainy teh next week and then I am off for 15 day vacation.  When I get back I hope its clear so I can contimue with my image.