Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Flats Reflection Issue

  • Please log in to reply
5 replies to this topic

#1 Peregrinatum

Peregrinatum

    Apollo

  • *****
  • topic starter
  • Posts: 1,170
  • Joined: 27 Dec 2018
  • Loc: South Central Valley, Ca

Posted 05 June 2020 - 04:23 PM

Hi all, looking for insight into removing some reflections from my flats.

 

Two flats below are filters Blue (left) and Green (right), same exposure and gain.

 

What are those small circles that are consistent in both images?  The large circles on the left are dust motes, but both images have the smaller circles.

 

Flats taken in living room with:

-flat panel, with white paper between C925HD and panel to diffuse light

-room was dim but not dark

-towel draped over OTA vents and imaging train to block stray light

ASI1600MM, ZWO 8 Position EFW, OAG, C925HD

 

UmYLRLbh.jpg


Edited by Peregrinatum, 05 June 2020 - 05:43 PM.


#2 H-Alfa

H-Alfa

    Viking 1

  • -----
  • Posts: 634
  • Joined: 21 Sep 2006
  • Loc: Spain

Posted 05 June 2020 - 04:29 PM

My bet would be that are dust motes on the CCD cover glass.
  • RossW and Peregrinatum like this

#3 jdupton

jdupton

    Mercury-Atlas

  • *****
  • Posts: 2,516
  • Joined: 21 Nov 2010
  • Loc: Central Texas, USA

Posted 05 June 2020 - 04:49 PM

Peregrinatum,

 

   Those both look normal to me. I may not be noticing which items you are concerned about. You can use the Dust Mote Calculator at the following link. Measure the sizes of each different spot you see and it will tell you where it is relative to the sensor. That should lead you to the possibly multiple surfaced that are giving rise to the spots. You may have motes on the Sensor itself, on the camera window, on the filters, or on any focal reducer or field flattener you may have in the optical train.

 

https://www.ccdware.com/resources/dust.cfm

 

 

John


  • Peregrinatum likes this

#4 Peregrinatum

Peregrinatum

    Apollo

  • *****
  • topic starter
  • Posts: 1,170
  • Joined: 27 Dec 2018
  • Loc: South Central Valley, Ca

Posted 05 June 2020 - 05:38 PM

Interesting, here is what the dust donut calculator says, and the dimensions of the camera:  dust donut ~ 8.4mm and sensor cover to sensor ~ 6.5mm

 

I will clean off the sensor cover tomorrow and try again... could dust be on the inside of the sensor cover?

 

l221Dqul.jpg

aMX4PGql.jpg



#5 jdupton

jdupton

    Mercury-Atlas

  • *****
  • Posts: 2,516
  • Joined: 21 Nov 2010
  • Loc: Central Texas, USA

Posted 05 June 2020 - 07:08 PM

Peregrinatum,

 

   Which did you measure for the distance? There were multiple sizes showing on the frames you posted. Is the 8.4 mm distance for the smallest ones?

 

 

John



#6 Peregrinatum

Peregrinatum

    Apollo

  • *****
  • topic starter
  • Posts: 1,170
  • Joined: 27 Dec 2018
  • Loc: South Central Valley, Ca

Posted 05 June 2020 - 07:28 PM

Peregrinatum,

 

   Which did you measure for the distance? There were multiple sizes showing on the frames you posted. Is the 8.4 mm distance for the smallest ones?

 

 

John

Yes it was for the smaller circles.


Edited by Peregrinatum, 05 June 2020 - 07:29 PM.



CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics