Equipment

LX200R PEC Results

Heres what my LX200R PEC looks raw following a Quadratic smooth in PEMPro. Its about 20 sec peak to peak. From what I can gather that's reasonable for an LX scope.

Heres what the PEC looks like after two runs. Red is the first (Pre-PEC); Blue is with PEC on and Green is the average. I'm still trying to work out why its worse after training!!

Making Flats with the DSI III Or

How to clean spots off your CCD really really carefully

I discovered soon after purchasing my DSI III that it had some pretty big dust spots somewhere in the optical train. I tried removing these post processing in PS CS3 but it left some fairly poor looking artefacts in the image (and of course I lost information as a result of the spots in the first place).

I decided to start looking at generating and removing these artefacts using Flats (basically a process where you take a carefully illuminated image that highlights unevenness and dust motes in the optical train and subtract them from your target image).

To determine how bad the optics were affected by dust, I setup the simple light table shown below and illuminated a piece of white paper (fairly evenly) with a lamp. In the process I discovered that the DSI USB connector was moving quite a bit causing the cam to connect and disconnect. After some online discussion I found that a couple of rubber bands fixed that up.

I setup Envisage as I had read online (from others a lot smarter than me) ie: with darks being subtracted and selected an exposure that would give an ADU of between 20-30K. I used FITS format to generate L,R,G,B images (about 10-20 exposures). I loaded these into CCDStack and created a colour final image that was pretty highly stretched. I could have also done this in PS CS3 using FITS Liberator and got the same result.

I was horrified to see an image with a whole lot of hard black spots and smearing. After some more online discussion I decided to try to clean the Cam itself. The steps I followed were:

1. Get a nice clean area setup

2. Get the tools you'll need for the cleaning process. I used the stuff in the image below.

• - New Camel hair brush; Blower; UHTC solution (you can get the formula from ASO at http://www.arksky.org/asoclean.htm ).
• - The balsa stick and lens cloth were used to clean off what appeared to be grease on the IR filter. This is the most dodgy step and I had to think 3 times before attempting it.

3. Remove the DSI Nosepiece. On the DSI III there is a round plastic insert which will fallout once the nosepiece is removed containing the IR filter

4. Remove this insert and the CCD chip (covered by what appears to be another coverslip) is exposed. Cover this over with the DSI cap as it appears to attract dust from everywhere in the room.

5. I first used the camel hair brush and blower on the IR Filter but it still showed grease marks. I then used the UHTC cleaner combined with a lint free lens cloth to carefully wipe the IR Filter (in one direction only). The balsa stick was used to provide a guide or former for the cloth. I was careful not to apply pressure while doing this.

6. I finally used the blower and camel hair brush then on the CCD coverslip itself. You need to do this under very good lighting and preferably under magnification as the dust and streaks can be very hard to see.

7. Reassemble and take test flats again.

Below are a couple of the results and I am now happy with the final one.

Post Cleaning  Effort #2                                                                         Final Cleaning Effort        

There's a lot of good information on the net on how to take and use Flats etc. A Google search will find most of them but a really good description of Dark, Flat and Bias Frame construction and usage can be found on the Ice and Space site by Eddie Trimarchi at http://www.iceinspace.com.au/index.php?id=63,211,0,0,1,0   The article includes a simple light box design (which I'll get around to building one of these days).

For now though I'll be taking twilight flats by imaging the sky during evening and/or morning twilight on the side of the zenith away from where the sun has set\risen. The sky should approximate uniform illumination quite well and the whole light and optical train telescope is all setup with little or no change ready for the imaging session. Important point is to use exactly the setup that you'll use to image including focus.

One problem I found with approach is that the brightness of the sky changes quickly with the onset of twilight and it can be hard to get the 5-10 good flats you need of around 20-30k ADU.

Once I get some decent weather I'll do some twilight flats and post some before and after shots.

Good luck and I take no responsibility for any of the instructions I've listed here.

 

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My Equipment

The Atik filter wheel and shutter from Scope Stuff fitted to the DSI Pro II & on the LX200R

 

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The LX200R