About Astrojohn

I am a science geek! Interests Astronomy, Skiing, Philosophy, basically any form of technology including writing automation software for my observatory. I will also share this with others using the same EQMOD/Astroart tool set.

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Flat Light.

This project was created due to the following requirements at the observatory:

  • Firstly, some dust on the filters caused doughnuts!

Flat frame taken using 'Flat Light' Through single filter

ADU counts darkest 10300 Lightest 10700  so a very small effect but correction of frames using flats takes out all these small srrors.. Don’t think you can get rid of it. Dust is a thing you have to live with and this is very very small dust magnified by increasing the contrast.

  • It is really difficult to get the light intensity for flats just right for shutter cameras
  • I needed a simple to build and rugged very flat light source.
  • I needed it to give me an ADU count on an SXVR-H18 of about 10000
  • It’s total cost needed to be as low as possible time and materials considered.

Ok so I bought an A3 Electro Luminescent panel from http://www.posterpoweruk.co.uk/page7.htm It is called a ‘white light sheet’ and includes a power supply.

I also ordered 2 sheets of Dark Grey Tinted Acrylic about A3 size. http://www.sheetplastics.co.uk/

Then went to the local DIY shop and bought:

  • Black electrical insulating tape
  • Black adhesive velcro (Both hook and loop required)
  • Black non adhesive velcro (Used to attach to the scope)

Now ready to build…

  • Test the White Light(EL) Panel and check which side is the ‘light’
  • Using the black insulating tape, stick it light side down onto the acrylic sheet, make sure there is no dust trapped between the two.
  • On the opposite site to the White Light sheet add another sheet of acrylic so there are two layers.
  • Seal the edges using the black insulating tape.
  • Leave enough space to attach the power supply to the acrylic sheet without is being closer than 1 inch to the EL sheet but on the same side as the EL sheet.
  • Use the adhesive velcro and the tape to secure the power supply to the acrylic but do not cover any power supply cooling holes.
  • Put two strips of adhesive velcro of the opposite type to the non adhesive velcro down the power supply side of the acrylic sheet to be able to hang the assembly on the front of your scope.

Your ready to take some flats. I used 5 second exposures for each filter position.

 

The resulting flats are really very good and consistant.

John.