TheSkySearchers

Hey all, I have been having some issues with my luminance flats and I thought someone out there in TSS-land may be able to steer me in the right direction. This has occurred on two separate imaging runs, on different nights. I take flats and flatdarks for every session; I only use a dark library for my master darks. The problem is the inability of the flats to subtract out two specific dust halos (and yes, I guess if I clean the filters and sensor which I plan to do soon the problem might go away.) But that's besides the point.

Here is a zoomed-in portion of my master flat: And here is a comparison of the result of processing the Lum with and without the masterflat. As you can see, all the dust motes have been removed except for the larger one on the top of the zoomed-in image (there is another almost identical problem in the bottom of the image, but not shown here). The exact same defect occurs in an earlier image of the sombrero galaxy.

Any idea why this is happening?

Strange! It seems to do an excellent job of removing all of the small dust motes (and you have several!). However, the one large "mote" that looks like an old fashioned telephone dial (located at about 1 o-clock) seems to be enhanced! You have me stumped with this one.

Is it possible that the large "mote" shows up on the master dark frame? Just making a wild guess here!

Steve

STEVE333 wrote: ↑Sun May 15, 2022 4:43 am Strange! It seems to do an excellent job of removing all of the small dust motes (and you have several!). However, the one large "mote" that looks like an old fashioned telephone dial (located at about 1 o-clock) seems to be enhanced! You have me stumped with this one.

Is it possible that the large "mote" shows up on the master dark frame? Just making a wild guess here!

Steve

Well, as you know, the dark frames are with the aperture closed, so there is no way the dust motes can enter in. I did check though - nope, not the issue. I'm starting to think that maybe the focus was different when the flats were taken (not sure how that would happen as I take the flats after the lights run but who knows). If the focus was off, the mote circles would either be slightly larger or smaller and the large ones would experience a larger degree of change. And this might explain the alternating concentric rings - maybe

Hi Michael,

You know that is strange. My last image (Whale and Hockey Stick Galaxies, I had two very large dust motes on my lights. I saw them during imaging and really didn't give it a second thought knowing that calibration would take care of them.

Well, calibration didn't take care of them!

In fact, what is a bit stranger (to me anyway), The motes mirrored themselves on opposite corners of the image (meridian flip???) in the Masterlight.

Never have had that happen before and they were easy to CloneStamp out, but I kind of put it behind me until your post.

I had used a new light panel to create the flats the first pass through WBPP. I also used bias and darks. I re-ran WBPP with new flats and dark flats and darks which did not help. I tried my old ipad to create the flats and still had the motes show up (with mirrors). I always shoot 50% ADU flats, so I tried creating 15, 30, and 70% ADU flats without any success. This is when I went back to the original flats/bias/darkd and pulled out the CloneStamp'er.

Then I went to work on locating the dust motes. Ended up that they were on the camera sensor window. Problem solved, but not really sure. Just FYI, I was using PI WBPP for calibration/registration/integration v2.4.1.

Probably not at all related to your issue Michael, but just rang a bell.